bluuebunny/crossref_metadata_2025 huggingface dataset:
THE STEINER CENTRE OF A SET OF POINTS: STABILITY, ECCENTRICITY, AND APPLICATIONS TO MOBILE FACILITY LOCATION
Authors: DUROCHER STEPHANE , KIRKPATRICK DAVID
Published: August 2006

The Euclidean centre (centre of the smallest enclosing sphere) of a set of points P in two or more dimensions is unstable; small perturbations at only a few points of P can result in an arbitrarily large relative change in the position of the Euclidean centre. Any centre function more stable than the Euclidean centre is eccentric; that is, its associated radius exceeds the radius of the smallest enclosing circle for some point sets P. Motivated by applications in mobile facility location (in which clients move continuously with some maximum velocity) we seek alternative notions of centrality that are stable while maintaining low eccentricity. In general there is a trade-off; centre functions with lower eccentricity are less stable. In an attempt to balance the conflicting goals of closeness of approximation and stability, we apply the Steiner centre, traditionally defined for convex polytopes, as a centre function of a set of points in the plane. Although previously defined, the notion of a Steiner centre had not been analyzed in terms of its approximation of the Euclidean centre. Exploiting the equivalence of the two definitions of the Steiner centre established by Shephard,27we prove the stability of the Steiner centre is π/4 and show that the associated radius is at most 1.1153 times the Euclidean radius of any point set P. It follows that a mobile facility located at the Steiner centre of the positions of a set of mobile clients remains close to the Euclidean centre of the clients yet never moves with relative velocity that exceeds 4/π.
An evaluation of the chemical attenuation capacity of UK mineral liner and geological barrier materials for landfill leachate components
Authors: Fannin C.A.
Published: August 2006

Chemical attenuation processes perform an important role in the retardation of substances within the hydrogeological environment. The extent of attenuation as described by the distribution coefficient
K
d
is highly dependent on the nature of the solid substrate and also the infiltrating solution. Published studies have presented data relevant to natural attenuation processes within sediments associated with contamination from industrial sources and associated with landfill leachates. This paper presents an evaluation of the attenuation capability of artificial mineral or natural geological barriers within the UK for heavy metals, ammonium and, indirectly, for organic substances. This paper confirms the high potential for heavy metals to be adsorbed to low-permeability sediments from dilute solutions; however, it also establishes that heavy metal distribution coefficients are significantly depressed in the presence of landfill leachate. This is likely to be due to competitive surface reactions and solution complexation. Attenuation coefficients were generally depressed for cadmium and zinc by over 50%, whereas copper and nickel attenuation coefficients can be depressed by two orders of magnitude. The experimental attenuation coefficients determined through this study can be used for modelling contaminant migration in the absence of site-specific data for both landfill-related and contaminated land scenarios.
A review of mecoprop attenuation in the subsurface
Authors: Buss S.R. , Thrasher J. , Morgan P. , Smith J.W.N.
Published: August 2006

Mecoprop is an acid herbicide that is widely used for agricultural, horticultural and domestic purposes. It is considered one of the key indicators of pollution from municipal solid waste landfill, as it is frequently identified in landfill leachate. Mecoprop is the most frequently occurring herbicide detected in UK groundwater and the second most common herbicide in UK surface waters. Mecoprop is water-soluble and subject to relatively little retardation by sorption processes, hence it is subject to relatively conservative transport in soils and aquifers. Once in the subsurface it can be persistent. Information and data to underpin the assessment of mecoprop fate and attenuation in the subsurface are therefore of particular importance. This paper reviews the processes that contribute to the attenuation of mecoprop in the subsurface, particularly in groundwater. Biodegradation of mecoprop is the only significant destructive attenuation mechanism operating under subsurface conditions. Biodegradation in topsoil has been relatively widely studied and is commonly observed, but the scientific literature on mecoprop biodegradation in the deeper subsurface is limited and indicates great variability as to the degree and rate at which it takes place, particularly in aerobic aquifers. The apparent recalcitrance under anaerobic conditions means that where it has been disposed of to landfill it is frequently among the most persistent organic compounds in chemically reducing leachate plumes. Mecoprop sorption to sediment surfaces is related to the organic and inorganic geochemistry of mecoprop and the sediment. It is suggested that the generally applied model that uses
K
OC
for predicting sorption of organic solutes may not be appropriate for use with mecoprop.
Deformation effects in rock massifs and their long-term monitoring
Authors: Košt'ák B.
Published: August 2006

Rock massifs are subject to long-term deformations, as well as to environmental effects. Decades of precise crack gauging have led to a series of qualified results of practical importance to geotechnical engineering. Slow deep-seated rock slope movements have been observed and monitored in cases where long-term stability was anticipated. In addition to movement trends, specific events of acceleration were detected and impulse periods determined. Examples in the field of geotechnics are given, which include an observed rock massif response to prestressed anchors, a history of slope instability affected by human interference, and evaluation of fault-controlled stability in a railway cutting affected by long-term rock weathering.
Mechanisms of slope failure in Valles Marineris, Mars
Authors: Neuffer D.P. , Schultz R.A.
Published: August 2006

The trough system of Valles Marineris, Mars contains numerous landslides in the large relief exposures (up to 8 km) of basaltic wall rock and soft interior layered deposits (ILDs). Eleven landslides, including eight circular failures, were mapped in the ILDs. Two wall rock landslide complexes and four ILD landslides were modelled using limit-equilibrium slope stability analysis to evaluate the mechanisms of slope failure. Wall rock landslide complexes in the Ophir and Hebes Chasmata required artesian fluid pressures of at least 41% of overburden pressure or ground accelerations of at least 0.19 Mars
g
for failure. Agreement between modelled and observed failure surface geometries and the difficulty of generating artesian pressures at a regional topographic high indicate that ground shaking from Marsquakes or impacts most likely triggered the modelled wall rock landslides. Triggering mechanisms, such as ground acceleration or fluid pressure, were also necessary for most other landslides in Valles Marineris wall rock. Given minimum rock mass strengths, ILD landslides in the Hebes and East Candor Chasmata did not require triggering mechanisms; thus, landslides in ILDs may be a result of gravitational, fluid, or seismic loading.
Hydrogeological potential of the deep Ecca aquifer of the Kalahari, southwestern Botswana
Authors: Cheney C.S. , Rutter H.K. , Farr J. , Phofuetsile P.
Published: August 2006

The Matsheng area, located in the Kalahari semi-desert of southwestern Botswana, has in recent years formed the focus for development in the Kgalagadi District. The availability of an adequate groundwater supply is critical to future development in the area, including the establishment of commercial ranching beyond the main centres of settlement. Although groundwater in the Ecca aquifer in this area was known to be saline, reports persisted that better quality groundwater, perhaps suitable for agriculture, existed, as is the case elsewhere in Botswana. This represented the main prospect of obtaining usable groundwater supplies for potential ranching areas in western Botswana. A detailed assessment has shown that high yielding Ecca aquifer horizons are present across the entire area but the groundwater is highly saline, with no evidence of freshening with depth. There was, in fact, evidence that salinity increased with development of boreholes. It was concluded that the Ecca groundwaters were not usable for any agricultural purpose but the slight improvement in quality on the northern margin of the area indicates that quality improves further to the north.
Sabellarids: a hidden danger or an aid to subsea pipelines?
Authors: Braithwaite C.J.R. , Robinson R.J. , Jones G.
Published: August 2006

Routine surveys of a subsea pipeline off the NE coast of Scotland in 2000 and 2002 revealed the presence of large numbers of encrusting mounds. These were perceived as a potential risk to the integrity of the pipeline and were subject to investigation.

The mounds are constructed by sabellarid worms. Individual worms trap sand from turbulent waters, cementing grains to form robust tubes and collectively forming structures up to 0.75 m in diameter, extending over kilometres of pipeline. Growth rates appear to be relatively rapid and the areas occupied increased significantly within the initial period of observation.

The mass and surface area of these structures could affect pipeline integrity in two ways: where the pipe is in span a dead load is applied as a direct consequence of the presence of the mounds. In addition, there is an increased lateral live-load as a result of the increase in surface area presented to currents. By contrast, overgrowth of the pipeline may ultimately offer additional protection. This account describes the nature of this novel addition to shallow water pipelines and assesses its likely impact. Observations in 2004 and 2005 indicated substantial reductions in the areas covered by sabellarid colonies and here at least whatever risk they may present has so far proved transitory.
Erasmus Darwin (1731–1802) and the principle of the overflowing well
Authors: Mather J.D.
Published: August 2006

In 1783 Erasmus Darwin, grandfather of the famous scientist Charles, and his family moved to Full Street in Derby, where renovations to the house included improvements to the water supply. He deepened an old polluted well near the house in the expectation that he would intersect the same water-bearing sand that fed St. Alkmund's Well about 800 m to the north. Good quality water was obtained, which overflowed at the surface. The success of his well depended on higher heads at depth in a zone of groundwater discharge rather than direct hydraulic continuity between sands in his well and those cropping out on higher ground to the west. Despite some claims, Darwin was not the first to state clearly the principle underlying overflowing wells. In Europe this distinction can be claimed by Bernard Palissy, writing some 200 years before Darwin. A hundred years later, Bernardino Ramazzini speculated correctly on the origin of the overflowing wells of Modena. Darwin's main contribution lies in his early application of geology to the solution of a water supply problem.
Evolution of Basal Ganglia Surgery for Movement Disorders
Authors: Gildenberg Philip L.
Published: August 2006

In 1942, it was thought that basal ganglia surgery would cause permanent unconsciousness and significant impairment of motor control. By 1947, when human stereotactic surgery was introduced, the first target was the globus pallidus in a patient with chorea. What happened during those 5 years to set the stage for stereotactic surgery? During the last half of the 19th century, it was first noted that motor disorders were often accompanied by atrophy of various parts of the basal ganglia, and when histopathology became part of necropsy, that relationship between movement disorders and the basal ganglia was strengthened. The impairment of fine motor control was noted in experiments that involved lesioning the basal ganglia, which led to the conclusion that disease of the basal ganglia might cause motor impairment. Finally, in 1939, Russel Meyers took the bold move of surgically resecting the head of the caudate nucleus at craniotomy in a patient with Parkinson’s disease, demonstrating that Dandy was wrong in the view that the basal ganglia were the center of consciousness, and that symptoms and motor control might be improved by caudate lesions without motor impairment. He reported his first patient in a meeting in 1940, which was published in 1942, and was encouraged to investigate basal ganglia surgery further. Although results were encouraging, the mortality rate was prohibitive. Since the introduction of pallidoansotomy in 1947, basal ganglia surgery has become both safe and effective and has been expanded and refined.
New Radiofrequency Coil Integrated with a Stereotactic Frame for Intraoperative MRI-Controlled Stereotactically Guided Brain Surgery
Authors: Taniguchi Hiroki , Muragaki Yoshihiro , Iseki Hiroshi , Nakamura Ryoichi , Taira Takaomi
Published: August 2006

Mislocalization errors caused by MR image distortions or brain shift are one of the main causes of complications after stereotactically guided neurosurgical procedures. A special device, which could ameliorate such effects and provide intraoperative acquisition of MR images of sufficient diagnostic accuracy, was developed. It is composed of a radiofrequency receiver coil integrated with a modified Komai stereotactic frame and a Sugita four-pin head holder. Clinical testing revealed that the use of the device during stereotactically guided procedures under the control of low magnetic field strength (0.3 T) intraoperative MRI ameliorates the effects of brain shift, and permits to obtain informative tissue samples and to perform aggressive removal of the lesion without any damage of the eloquent cerebral structures. The possibility of an easy shift from a stereotactically guided to a routine microneurosurgical procedure represents an additional benefit of the developed device.
Stereotactic Imaging for Radiosurgery: Localization Accuracy of Magnetic Resonance Imaging and Positron Emission Tomography Compared with Computed Tomography
Authors: Mori Yoshimasa , Hayashi Naoki , Iwase Mikio , Yamada Masami , Takikawa Yukinori , Uchiyama Yukio , Oda Kyota , Kaii Osamu
Published: August 2006

Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) provide complementary information for treatment planning in stereotactic radiosurgery. We evaluated the localization accuracy of MRI and PET compared with CT. Two kinds of phantoms applicable to the Leksell G stereotactic skull frame (Elekta, Tokyo) were developed. Deviations of measured coordinates at target points (x = 50, 100, 150; y = 50, 100, 150) were determined on different axial planes (z = 30–140 for MRI and CT study and Z = 50–120 for PET and CT study). For MRI, the deviations were no more than 0.8 mm in each direction. For PET, the deviations were no more than 2.7 mm. For both imaging modalities studied, accuracy was at or below the imaging resolution (pixel size) and should be considered useful for clinical stereotactic planning purposes.
MR Spectroscopic Changes in the Rat Hippocampus following Proton Radiosurgery
Authors: Rabinov J.D. , Cheng L.L. , Lee P.L. , Brisman J.L. , Loeffler J.S. , Cole A.J. , Cosgrove G.R. , Bussiere M.R. , Chaves T. , Gonzalez R.G.
Published: August 2006

Purpose: To identify MR spectroscopic changes in the rat hippocampus following proton radiosurgery. Methods and Materials: A group of 12 rats were treated with Bragg peak proton beam irradiation involving the right hippocampus. Single doses of 30 CGE, 50 CGE, 70 CGE, 90 CGE were delivered to groups of 3 animals using single fraction technique. Animals were imaged using a standard 3 T GE Signa MRI at 4 months following treatment. An untreated animal was also studied. A 3″ surface coil was employed to obtain T1 weighted coronal pre- and post-gadolinium images (TR 600 and TE 30) and dual echo T2 weighted coronal images (TR 3000, TE 30/90). Volumetric analysis with custom software was done to evaluate areas of increased signal on T2 weighted images and the development of hydrocephalus was examined. Animals were sacrificed and specimens of the treated hippocampus were harvested for High Resolution Magic Angle Spinning MR Spectroscopy (HRMAS) followed by histopathology of the tissue samples. Peak values of choline, creatine, N-acetyl aspartate and lipids were evaluated and compared. Results: Peak tissue injury occurred in the surviving 90 CGE animal by both T2 weighted and post-gadolinium imaging. Gadolinium enhancement was seen in decreasing volumes of tissue at dosage levels from 90 to 50 CGE. Hydrocephalus was seen on the untreated side in the 90 CGE animal likely because of mass effect, while it was seen in small degrees in the side of treatment in the 70 and 50 CGE animals. Histopathology showed changes at 90 and 70 CGE, but not at 50 or 30 CGE at this time point using H and E stains. HRMAS showed spectroscopic changes in the surviving 90 and 70 CGE animals but not in the 50 and 30 CGE animals. Statistical significance was not reached because of the small sample size. Conclusions: Following single dose proton radiosurgery of rat hippocampus, HRMAS is able to identify metabolic changes induced by radiation. Studies built on these principles may help develop non-invasive MR spectroscopic methods to distinguish radiation changes from tumor recurrence.
Troglitazone and 9cis,11trans,13trans-Conjugated Linolenic Acid: Comparison of Their Antiproliferative and Apoptosis-Inducing Effects on Different Colon Cancer Cell Lines
Authors: Yasui Y. , Hosokawa M. , Kohno H. , Tanaka T. , Miyashita K.
Published: August 2006

Background: We have previously reported that troglitazone, a synthetic ligand for peroxisome proliferator-activated receptor γ (PPARγ), and bitter gourd seed oil rich in 9cis,11trans,13trans-conjugated linolenic acid (9c,11t,13t-CLN) prevent colon carcinogenesis. To evaluate the chemotherapeutic effect and potency of these compounds on colon cancer cells, we investigated their antiproliferative and apoptosis-inducing effects using different human colon cancer cell lines. Methods: The antiproliferative and apoptosis-inducing effects of troglitazone and 9c,11t,13t-CLN were evaluated and compared using HT-29, DLD-1 and Caco-2 cells at different stages of enterocytic differentiation. Results: Troglitazone and 9c,11t,13t-CLN decreased cell viability and induced apoptosis in three colon cancer cell lines. The susceptibility of HT-29, which expresses PPARγ at high levels, to troglitazone and 9c,11t,13t-CLN was higher than that of Caco-2 cells with low levels of PPARγ. Conclusion: Troglitazone and 9c,11t,13t-CLN exhibited more effective chemotherapeutic effects on HT-29 cells than on Caco-2 cells.
Investigation of Potential Antibacterial Properties of Methanol Extracts from Fungus Ganoderma applanatum
Authors: Moradali Mohammad-Fata , Mostafavi Hossien , Hejaroude Ghorban-Ali , Tehrani Abbas Sharifi , Abbasi Mehrdad , Ghods Shirin
Published: August 2006

In this study we searched for antibacterial compounds in methanol extracts of three layers (tube layer, context and cutis) of Ganoderma applanatum fruit body against Bacillus subtilis ATCC 6051 as a gram-positive bacterium and Escherichia coli ATCC 25922 and Pseudomonas syringae pv. syringae DPIC 219 as gram-negative bacteria. We found antibacterial properties in all three layers only against gram-negative bacteria. The fractions were isolated and purified by thin layer chromatography (TLC) and high-performance liquid chromatography. After purification, four major compounds – A, B, C and D – were tested for antibacterial properties, and B and D were found to possess antibacterial properties. The results of TLC and spectral data, including mass spectra and 1H NMR of compounds B and C, showed that they were saturated fatty acids and compound D was palmitic acid (hexadecanoic acid) (16:0).
Fluconazole and Itraconazole Resistance of Yeasts Isolated from the Bloodstream and Catheters of Hospitalized Pediatric Patients
Authors: Giusiano Gustavo , Mangiaterra Magdalena , Garcia Saito Viviana , Rojas Florencia , Gómez Verónica , Díaz María Cristina
Published: August 2006

Background: In critically ill children, Candida species and other yeasts appear as an important nosocomial pathogen. The emerging fungal pathogens are usually less susceptible to azole compounds, and the management of such infections could be problematic. Methods: 6,065 bloodstream cultures and 627 catheters from intensive care units and hospitalized oncology pediatric patients were studied. Antifungal susceptibility testing of isolates was performed according to the reference broth microdilution method describedby the National Committee for Clinical Laboratory Standards (M27-A). Results: We found a low activity of fluconazole (FCZ) and itraconazole (ITZ) against Candida glabrata, C. albicans, C. tropicalis and C. haemulonii. Resistant strains to FCZ and ITZ were detected. Conclusion: Results reveal the emergence of antifungal-resistant species and a change in the predominant role of C. albicans as a cause of candidemia in hospitalized children.
Hepatocyte Growth Factor Is a Better Indicator of Therapeutic Response than C-Reactive Protein within the First Day of Treatment in Pneumonia
Authors: Abednazari Hossein , Xu Junyang , Millinger Eva , Brudin Lars , Forsberg Pia , Nayeri Fariba
Published: August 2006

Acute bacterial infectious diseases are mostly treated empirically at admission before the culture results are available. According to the risk for serious complications in the case of therapeutic failure, it is important to evaluate the therapy results and change to a more appropriate antibiotic regime as soon as possible. In the present study, 40 patients with X-ray-verified community-acquired pneumonia were examined and blood specimens were collected before and within 24 h of treatment. Body temperature, C-reactive protein (CRP) and hepatocyte growth factor (HGF) were investigated. Thirty-two patients received an appropriate initial antibiotic therapy regarding clinical outcome, but in 8 patients the treatment was changed because of therapy failure. Changes of HGF levels after 18–24 h of treatment could predict the therapeutic results accurately in 38 of 40 cases (sensitivity 100%, specificity 94%, positive likelihood ratio 16.0). HGF was significantly better to predict therapy outcome than CRP (p < 0.0001).
Advanced Glycation End Products
Authors: Goldin Alison , Beckman Joshua A. , Schmidt Ann Marie , Creager Mark A.
Published: August 2006

Advanced glycation end products (AGEs) are proteins or lipids that become glycated after exposure to sugars. AGEs are prevalent in the diabetic vasculature and contribute to the development of atherosclerosis. The presence and accumulation of AGEs in many different cell types affect extracellular and intracellular structure and function. AGEs contribute to a variety of microvascular and macrovascular complications through the formation of cross-links between molecules in the basement membrane of the extracellular matrix and by engaging the receptor for advanced glycation end products (RAGE). Activation of RAGE by AGEs causes upregulation of the transcription factor nuclear factor-κB and its target genes. Soluble AGEs activate monocytes, and AGEs in the basement membrane inhibit monocyte migration. AGE-bound RAGE increases endothelial permeability to macromolecules. AGEs block nitric oxide activity in the endothelium and cause the production of reactive oxygen species. Because of the emerging evidence about the adverse effects of AGEs on the vasculature of patients with diabetes, a number of different therapies to inhibit AGEs are under investigation.
Fluctuations in an Equilibrium Convective Ensemble. Part I: Theoretical Formulation
Authors: Craig George C. , Cohen Brenda G.
Published: August 2006

To provide a theoretical basis for stochastic parameterization of cumulus convection, the equilibrium fluctuations of a field of cumulus clouds under homogeneous large-scale forcing are derived statistically, using the Gibbs canonical ensemble from statistical mechanics. In the limit of noninteracting convective cells, the statistics of these convective fluctuations can be written in terms of the large-scale, externally constrained properties of the system. Using this framework, the probability density function of individual cloud mass fluxes is shown to be exponential. An analytical expression for the distribution function of total mass flux over a region of given size is also derived, and the variance of this distribution is found to be inversely related to the mean number of clouds in the ensemble. In a companion paper, these theoretical predictions are tested against cloud resolving model data.
Fluctuations in an Equilibrium Convective Ensemble. Part II: Numerical Experiments
Authors: Cohen Brenda G. , Craig George C.
Published: August 2006

The theoretical predictions derived in Part I of this study for the equilibrium fluctuations of an idealized ensemble of noninteracting, pointlike cumulus clouds are tested against three-dimensional cloud resolving model (CRM) simulations of radiative–convective equilibrium. Simulations with different radiative cooling rates are used to give a range of cloud densities, while imposed vertical wind shear of different strengths is used to produce different degrees of convective organization. The distribution of mass flux of individual clouds is found to be exponential in all simulations, in agreement with the theory. The distribution of total mass flux over a finite region also agrees well (to within around 10%) with the theoretical prediction for all simulations, but only after a correction to the modeled variance to take account of the finite size of clouds has been made. In the absence of imposed vertical wind shear, some spatial clustering of convective cells is observed at lower forcings (−2 and −4 K day−1) on a scale of 10–20 km, while at higher forcings (−8, −12, and −16 K day−1), there is a tendency toward spatial regularity on the same scale. These localized cloud interactions, however, appear to have little effect on the magnitude of the mass flux variability. Surprisingly, the convective organization obtained in the simulations with vertical wind shear has only a small effect on the mass flux statistics, even though it shows clearly in the location of the clouds.
Regimes in Simple Systems
Authors: Lorenz Edward N.
Published: August 2006

Dynamical systems possessing regimes are identified with those where the state space possesses two or more regions such that transitions of the state from either region to the other are rare. Systems with regimes are compared to those where transitions are impossible.

A simple one-dimensional system where a variable is defined at N equally spaced points about a latitude circle, once thought not to possess regimes, is found to exhibit them when the external forcing F slightly exceeds its critical value F* for the appearance of chaos. Regimes are detected by examining extended time series of quantities such as total energy. A chain of k* fairly regular waves develops if F < F*, and F* is found to depend mainly upon the wavelength L* = N/k*, being greatest when L* is closest to a preferred length L0. A display of time series demonstrates how the existence and general properties of the regimes depend upon L*.

The barotropic vorticity equation, when applied to an elongated rectangular region, exhibits regimes much like those occurring with the one-dimensional system. A first-order piecewise-linear difference equation produces time series closely resembling some produced by the differential equations, and it permits explicit calculation of the expected duration time in either regime. Speculations as to the prevalence of regimes in dynamical systems in general, and to the applicability of the findings to atmospheric problems, are offered.
Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part I: Barotropic Critical Region
Authors: Rivière G. , Joly A.
Published: August 2006

By using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows, this paper investigates the role of the large-scale deformation field on extratropical cyclones and especially on their explosive growth in the jet-exit region. Theoretical ideas are tested by decomposing the atmospheric flow into a high- and a low-frequency part and by analyzing four-dimensional variational data assimilation (4DVAR) reanalysis data of the Fronts and Atlantic Storm-Track Experiment (FASTEX) during February 1997 as well as reanalysis data for the end of December 1999.

Regions where the low-frequency deformation magnitude is greater than the absolute value of the low-frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located. These regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low-frequency large-scale upper-tropospheric jet but cannot be detected by looking separately at the deformation or vorticity. Transitions from one such large-scale region to the next furthermore can be accompanied by a sudden change of the dilatation axes orientation: this combination defines a barotropic critical region (BtCR). Reasons why a BtCR is a specific place where barotropic development is likely to occur are exposed. Two very differently located BtCR regions in two apparently similar zonal-like weather regimes are shown to be the preferred regions where synoptic eddies tend to cross the jet from the south to the north.

BtCRs are also special regions where constructive association between barotropic and baroclinic processes is favored, indeed constrained to cooperate. This is illustrated through the detailed analysis of the last growth stage of Intensive Observation Period 17 (IOP17) of FASTEX. It happens precisely around a BtCR area located in the jet-exit region. Two processes explain this IOP17 development; one involves the barotropic generation rate resulting from the low crossing the BtCR and the other one is baroclinic interaction, which is strongly maintained far away from the baroclinicity maximum because of the new favorable baroclinic configuration resulting from the first process.
Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part II: Baroclinic Critical Region
Authors: Rivière G. , Joly A.
Published: August 2006

Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2m − ζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity.

While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.
Collisions of Small Drops in a Turbulent Flow. Part III: Relative Droplet Fluxes and Swept Volumes
Authors: Pinsky M. B. , Khain A. P. , Grits B. , Shapiro M.
Published: August 2006

Swept volumes of cloud droplets with radii below 20 μm are calculated under conditions typical of atmospheric cloud turbulence characterized by enormous values of Reynolds numbers, high turbulent intermittency, and characteristic values of the dissipation rate. To perform the calculations, the motion equation for small droplets proposed by Maxey is generalized for Stokes numbers St > 0.1, which allows one to simulate relative droplet motion even for very high turbulence intensities typical of deep cumulus clouds. Analytical considerations show that droplet motion is fully determined by turbulent shears and the Lagrangian accelerations.

A new statistical representation of a turbulent flow has been proposed based on the results of the scale analysis of turbulence characteristics and those related to the droplet motion. According to the method proposed, statistical properties of turbulent flow are represented by a set of noncorrelated samples of turbulent shears and Lagrangian accelerations. Each sample can be assigned to a certain point of the turbulent flow. Each such point can be surrounded by a small “elementary” volume with linear length scales of the Kolmogorov length scale, in which the Lagrangian acceleration and turbulent shears can be considered as uniform in space and invariable in time.

This present study (Part III) investigates the droplet collisions in a turbulent flow when hydrodynamic droplet interaction (HDI) is disregarded. Using a statistical model, long series of turbulent shears and accelerations were generated, reproducing probability distribution functions (PDF) at high Reynolds numbers, as they were obtained in recent laboratory and theoretical studies. Swept volumes of droplets are calculated for each sample of an acceleration–shear pair, and the PDF of swept volumes is calculated for turbulent parameters typical of cloud turbulence. The effect of turbulent flow intermittency manifests itself in two aspects: 1) an increase of swept volume variance with increasing Reynolds number, and 2) formation of the swept volume PDF that has a sharp maximum and an elongated tail.

In spite of the fact that the magnitude of the mean swept volume increases significantly with Reynolds number and the dissipation rate, this increase does not exceed ∼60% of pure gravity values even under turbulent conditions typical of strong cumulus clouds. A comparison with the classical results of Saffman and Turner is presented and discussed.
Observational Analysis of a Gust Front to Bore to Solitary Wave Transition within an Evolving Nocturnal Boundary Layer
Authors: Knupp Kevin
Published: August 2006

The evolution of a gust front to bore to solitary wave transition, and comprehensive information on the evolving nocturnal boundary layer (NBL) associated with this change, are described with analysis of radar and profiler measurements. The observations were obtained on 21 June 2002 in the Oklahoma panhandle during the International H2O Project. The evolution of this system, from a strong bore (initiated by a vigorous gust front) to a solitary wave, was observed over a 4-h period with Doppler radar and surface measurements. Detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers, a lidar ceilometer, and a microwave profiling radiometer.

A strong bore was initiated by an extensive gust front that perturbed an incipient NBL whose development (prior to sunset) was enhanced by shading from the parent mesoscale convective system. At the time of bore formation, the NBL was about 300 m deep and exhibited a surface temperature about 4 K less than the afternoon maximum. Initially, the bore assumed kinematic properties similar to those of a gust front. As the NBL stabilized, the bore matured and exhibited undular formations over 30–60-km segments along the bore axis. A 30-km-wide cloud field accompanied the mature bore system within three hours of its formation. System-relative airflow within the cloud field was front-to-rear and exhibited a primary hydraulic jump updraft (4–5 m s−1 magnitude) within the bore core. The bore core exhibited a low, smooth cloud base, a cloud depth of 2.5 km, nearly adiabatic liquid water content, and pronounced turbulence. The maximum parcel displacements within the bore were about 2 km (sufficient for marginal convective initiation), and the net parcel displacement from before to after bore passage was 0.6–0.9 km.
On the Self-Maintenance of Midlatitude Jets
Authors: Robinson Walter A.
Published: August 2006

In this paper an atmospheric jet is considered self-maintaining if the overall effect of baroclinic eddies is to preserve or enhance its westerly shear with height. Observations suggest that the wintertime jets in Earth’s atmosphere are self-maintaining. This has implications for the intrinsic variability of these jets—the annular modes—and for how the extratropics respond to tropical warming.

The theory of quasigeostrophic eddy–zonal flow interactions is employed to determine how a jet can be self-maintaining. Whether or not a jet is self-maintaining is found to depend sensitively on the meridional distribution of the absorption of wave activity.

The eddy driving of the jet in a simple two-level model of the global circulation is examined. It is found that, with approximately wintertime settings of parameters (a radiative equilibrium equator–pole temperature contrast of 60 K), the midlatitude jets in this model are self-maintaining. The jet is not self-maintaining, however, when the radiative equilibrium equator-to-pole temperature contrast is reduced below a critical value (∼24 K temperature contrast). Eddy amplitudes are also greatly reduced, in this case. The transition to a self-maintaining jet, as the radiative equilibrium temperature contrast is increased, suggests a set of feedback mechanisms that involve the strength of the baroclinicity in the jet center and where baroclinic eddies are absorbed in the subtropics. A barotropic eastward force applied to the model Tropics causes a poleward shift in the latitudes of greatest eddy absorption and induces a transition from a non-self-maintaining to a self-maintaining jet.

Self-maintaining behavior ultimately disappears, as the equator–pole thermal contrast, and thus the eddies, are strengthened. The flow is then highly disturbed and no longer dominated by wavelike baroclinic eddies.
Large-Eddy Simulation of Stably Stratified Atmospheric Boundary Layer Turbulence: A Scale-Dependent Dynamic Modeling Approach
Authors: Basu Sukanta , Porté-Agel Fernando
Published: August 2006

A new tuning-free subgrid-scale model, termed locally averaged scale-dependent dynamic (LASDD) model, is developed and implemented in large-eddy simulations (LES) of stable boundary layers. The new model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. Overall, the agreement between the statistics of the LES-generated turbulence and some well-established empirical formulations and theoretical predictions (e.g., the local scaling hypothesis) is remarkable. Moreover, the simulated statistics obtained with the LASDD model show relatively little resolution dependence for the range of grid sizes considered here. In essence, it is shown here that the new LASDD model is a robust subgrid-scale parameterization for reliable, tuning-free simulations of stable boundary layers, even with relatively coarse resolutions.
Predictability of Precipitation from Continental Radar Images. Part IV: Limits to Prediction
Authors: Germann Urs , Zawadzki Isztar , Turner Barry
Published: August 2006

Predictability of precipitation is examined from storm to synoptic scales through an experimental approach using continent-scale radar composite images. The lifetime of radar reflectivity patterns in Eulerian and Lagrangian coordinates is taken as a measure of predictability. The results are stratified according to scale, location, and time in order to determine how predictability depends on these parameters. Three companion papers give a detailed description of the methodology, and present results are obtained for 143 hours of North American warm season rainfall with emphasis on lifetime, scale dependence, optimum smoothing of forecast fields, and predictability in terms of probabilistic rainfall rates.

This paper discusses the sources of forecast uncertainty and extends the analysis to a total of 1424 hours of rainfall. In a Lagrangian persistence framework the predictability problem can be separated into a component associated with growth of precipitation and a component associated with changes in the storm motion field. The role of changes in the motion field turned out to be small but not negligible. A stratification of lifetime according to location reveals the regions with high predictability and significant nonstationary storm motion.

This work is of high practical significance for three reasons: First, Lagrangian persistence of radar patterns was proved to have skill for probabilistic precipitation nowcasting. The discussion of the sources of uncertainty provides a guideline for further improvements. Second, a scale- and location-dependent benchmark is obtained against which the progress of other precipitation forecasting techniques can be evaluated. And, third, the experimental approach to predictability presented in this paper is a valuable contribution to the fundamental question of predictability of precipitation.
Optical and Microphysical Properties of Upper Clouds Measured with the Raman Lidar and Hydrometeor Videosonde: A Case Study on 29 March 2004 over Tsukuba, Japan
Authors: Sakai Tetsu , Orikasa Narihiro , Nagai Tomohiro , Murakami Masataka , Kusunoki Kenichi , Mori Kazumasa , Hashimoto Akihiro , Matsumura Takatsugu , Shibata Takashi
Published: August 2006

Optical and microphysical properties of the upper clouds at an altitude range of 5–11 km were measured over Tsukuba, Japan, on 29–30 March 2004 using a ground-based Raman lidar and a balloon-borne hydrometeor videosonde (HYVIS). The Raman lidar measured the vertical distributions of the particle extinction coefficient, backscattering coefficients, depolarization ratio, and extinction-to-backscatter ratio (lidar ratio) at 532 nm; further, it measured the water vapor mixing ratio. The HYVIS measured the vertical distributions of the particle size, shape, cross-sectional area, and number concentration of the cloud particles by taking microscopic images. The HYVIS measurement showed that the cloud particles were ice crystals whose shapes were columnar, bulletlike, platelike, and irregular, and 7–400 μm in size. The Raman lidar measurement showed that the depolarization ratio ranged from 0% to 35% and the lidar ranged from 0.3 to 30 sr for the clouds in ice-saturated air. The comparison between the measured data and theoretical calculations of the cloud optical properties suggests that the observed variations in the depolarization ratio and lidar ratio were primarily due to the variation in the proportion of the horizontally oriented ice crystals in the clouds. The optical thickness of the cloud obtained from the lidar was about 2 times lower than that calculated from the HYVIS data, and the maximum extinction coefficient was about 5 times lower than the HYVIS data. The most probable reason for the differences is the horizontal inhomogeneities of the cloud properties between the measurements sites for the two instruments.
On the Role of Clouds and Moisture in Tropical Waves: A Two-Dimensional Model Study
Authors: Zurovac-Jevtić Danče , Bony Sandrine , Emanuel Kerry
Published: August 2006

Observations show that convective perturbations of the tropical atmosphere are associated with substantial variations of clouds and water vapor. Recent studies suggest that these variations may play an active role in the large-scale organization of the tropical atmosphere. The present study investigates that possibility by using a two-dimensional, nonrotating model that includes a set of physical parameterizations carefully evaluated against tropical data. In the absence of cloud–radiation interactions, the model spontaneously generates fast upwind (eastward) moving planetary-scale oscillations through the wind-induced surface heat exchange mechanism. In the presence of cloud–radiative effects, the model generates slower upwind (eastward) propagating modes in addition to small-scale disturbances advected downwind (westward) by the mean flow. Enhanced cloud–radiative effects further slow down upwind propagating waves and make them more prominent in the spectrum. On the other hand, the model suggests that interactions between moisture and convection favor the prominence of moist Kelvin-like waves in tropical variability at the expense of small-scale advective disturbances. These numerical results, consistent with theoretical predictions, suggest that the interaction of water vapor and cloud variations with convection and radiation plays an active role in the large-scale organization of the tropical atmosphere.
Design and Analysis of a Tool for Planning and Simulating Dynamic Vertical Transport
Authors: Cortés Pablo , Muñuzuri Jesús , Onieva Luis
Published: August 2006

Nowadays, most of the main companies in the vertical transport industry are researching tools capable of providing support for the design process of elevator systems. Numerous decisions have to be taken to obtain an accurate, comfortable, and high-quality service. Effectively, the optimization algorithm is a key factor in the design process, but so are the number of cars being installed, their technical characteristics, the kinematics of the elevator group, and some other design parameters, which cause the selection task of the elevator system to be a complex one. In this context, the design of decision support tools is becoming a real necessity that most important companies are including as part of their strategic plans. In this article, the authors present a user-friendly planning and simulating tool for dynamic vertical traffic. The tool is conceptualized for giving support in the planning and design stage of the elevator system, in order to collaborate in the selection of the type of elevator (number, type of dynamic, capacity, etc.) and the optimization algorithm.