bluuebunny/crossref_metadata_2025 huggingface dataset:
Contributions of Intrinsic Membrane Dynamics to Fast Network Oscillations With Irregular Neuronal Discharges
Authors: Geisler Caroline , Brunel Nicolas , Wang Xiao-Jing
Published: August 2005

During fast oscillations in the local field potential (40–100 Hz gamma, 100–200 Hz sharp-wave ripples) single cortical neurons typically fire irregularly at rates that are much lower than the oscillation frequency. Recent computational studies have provided a mathematical description of such fast oscillations, using the leaky integrate-and-fire (LIF) neuron model. Here, we extend this theoretical framework to populations of more realistic Hodgkin–Huxley-type conductance-based neurons. In a noisy network of GABAergic neurons that are connected randomly and sparsely by chemical synapses, coherent oscillations emerge with a frequency that depends sensitively on the single cell's membrane dynamics. The population frequency can be predicted analytically from the synaptic time constants and the preferred phase of discharge during the oscillatory cycle of a single cell subjected to noisy sinusoidal input. The latter depends significantly on the single cell's membrane properties and can be understood in the context of the simplified exponential integrate-and-fire (EIF) neuron. We find that 200-Hz oscillations can be generated, provided the effective input conductance of single cells is large, so that the single neuron's phase shift is sufficiently small. In a two-population network of excitatory pyramidal cells and inhibitory neurons, recurrent excitation can either decrease or increase the population rhythmic frequency, depending on whether in a neuron the excitatory synaptic current follows or precedes the inhibitory synaptic current in an oscillatory cycle. Detailed single-cell properties have a substantial impact on population oscillations, even though rhythmicity does not originate from pacemaker neurons and is an emergent network phenomenon.
Heat Shock–Mediated Thermoprotection of Larval Locomotion Compromised by Ubiquitous Overexpression of Hsp70 inDrosophila melanogaster
Authors: Klose Markus K. , Chu David , Xiao Chengfeng , Seroude Laurent , Robertson R. Meldrum
Published: August 2005

Maintaining the competence of locomotor circuitry under stressful conditions can benefit organisms by enabling locomotion to more tolerable microhabitats. We show that prior heat shock protects locomotion and the locomotor central pattern generator of larval Drosophila against subsequent hyperthermic stress. We combined molecular genetic, electrophysiological, and behavioral techniques to investigate heat shock–mediated thermoprotection. Prior heat shock increased the distance traveled by larvae during hyperthermia before failure. The frequency of the rhythm of peristaltic locomotor contractions and the velocity of locomotion were both less thermosensitive after heat shock and were less susceptible to failure at high temperatures. Rhythmic coordinated motor patterns, recorded intracellularly as excitatory junction potentials in body wall muscles of dissected preparations, were centrally generated because patterns could still be generated in the absence of sensory feedback (sensory function disrupted with shibire). Prior heat shock protected central circuit operation during hyperthermic stress by increasing the temperature at which it failed. Overexpression of Hsp70 after a heat shock using transgenic flies ( traII) did not enhance thermoprotection, as expected, but had deleterious effects on parameters of behavior.
A comparative genetic map of the turkey genome
Authors: Reed K.M. , Chaves L.D. , Hall M.K. , Knutson T.P. , Harry D.E.
Published: August 2005

Genetic markers (microsatellites and SNPs) were used to create and compare maps of the turkey and chicken genomes. A physical map of the chicken genome was built by comparing sequences of turkey markers with the chicken whole-genome sequence by BLAST analysis. A genetic linkage map of the turkey genome (Meleagris gallopavo) was developed by segregation analysis of genetic markers within the University of Minnesota/Nicholas Turkey Breeding Farms (UMN/NTBF) resource population. This linkage map of the turkey genome includes 314 loci arranged into 29 linkage groups. An additional 40 markers are tentatively placed within linkage groups based on two-point LOD scores and 16 markers remain unlinked. Total map distance contained within linkage groups is 2,011 cM with the longest linkage group (47 loci) measuring 413.3 cM. Average marker interval over the 29 linkage groups was 6.4 cM. All but one turkey linkage group could be aligned with the physical map of the chicken genome. The present genetic map of the turkey provides a comparative framework for future genomic studies.
Mouse Anterior Pituitary Gland: Analysis by Ion Trap Mass Spectrometry
Authors: Blake Charles A. , Kakhniashvili David G. , Goodman Steven R.
Published: August 2005

We investigated the proteome of the anterior pituitary gland (AP) in a species in which the genome has been sequenced. Subcellular fractions of APs from 2-month-old male mice were prepared for protein denaturation, treatment with trypsin and analyses utilizing micro liquid chromatography tandem mass spectrometry and the database search software SEQUEST. In the nuclear, non-nuclear 100,000 g and cytosolic fractions, we identified 49, 36 and 68 different proteins, respectively. A total of 115 distinct proteins were detected. We identified growth hormone, prolactin, pro-opiomelanocortin, the α-subunit for the glycoprotein hormones, and luteinizing hormone-β. Groups of other identified proteins included hormone-processing, secretion granule-associated, non-hormonal endoplasmic reticulum-associated, calcium-binding, protein kinase C-associated, histones, non-histone chromosomal, other RNA-binding, heterogeneous nuclear ribonucleoproteins, splicing factors, helicases, lamins, ribosomal, microtubule-associated, microfilament-associated, adenosine triphosphate- and guanosine triphosphate-associated, tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation, enzymes in glycolysis and the tricarboxylic and urea cycles and the pentose phosphate path, heat-shock, glutathione-associated, peroxidases, ubiquitin-associated, catabolic, protease inhibitors, other, and blood proteins. The 115 proteins reported in this study and the 145 proteins reported in a previous study on the AP of the adult male Golden Syrian hamster are compared and form a foundation for defining the proteome in normal adult male AP.
Obstructing Colorectal Carcinoma: Outcome and Risk Factors for Morbidity and Mortality
Authors: Álvarez JoséA. , Baldonedo Ricardo F. , Bear Isabel G. , Truán Nuria , Pire Gerardo , Álvarez Paloma
Published: August 2005

Background/Aims: Emergency surgery for colorectal cancer is widely thought to be associated with high morbidity and mortality. The aim of this study was to assess the operative results of patients who had emergency operations for obstructing colorectal cancer. Clinical factors that might influence the outcome were also evaluated. Patients and Methods: This is a retrospective study including 83 patients who underwent emergency operations for completely obstructing colorectal cancers from 1991 to 2002. Demographic, clinical, and pathological variables were examined. Their influence on major morbidity and mortality was assessed using univariate and multivariate analyses. Results: The overall and major morbidity rate was 67.5 and 32.5%, respectively. Mortality was 10.8%. Univariate analysis showed that high ASA class and perioperative blood transfusion were significantly associated with major complication, whereas older age and high APACHE II were linked to mortality. Independent risk factors for major morbidity were perioperative blood transfusion and high ASA class. The only independent predictor of postoperative death was high APACHE II score. Conclusions: Emergency surgery for obstructing colorectal carcinoma carries a negative impact on outcome. Patients with risk factors should undergo safe and least risky procedures. Moreover, their presence might help in selecting patients for intensive treatment after surgery.
Cognitive Impairment Is the Major Risk Factor for Development of Geriatric Syndromes during Hospitalization: Results from the GIFA Study
Authors: Mecocci Patrizia , von Strauss Eva , Cherubini Antonio , Ercolani Sara , Mariani Elena , Senin Umberto , Winblad Bengt , Fratiglioni Laura
Published: August 2005

Objective: To detect the main factors associated with the occurrence of specific geriatric syndromes (namely pressure sores, fecal incontinence, urinary incontinence and falls) in elderly patients during hospitalization. Design: Observational prospective study. Setting: Eighty-one community and university hospitals throughout Italy. Participants: 13,729 patients aged 65 years and more, consecutively admitted to medical or geriatric acute wards during 20 months in the period between 1991 and 1998. Measurements: Occurrence of pressure sores, fecal incontinence, urinary incontinence and falls during the stay in hospital. Results: Pressure sores were already present in 3% of hospitalized subjects, fecal incontinence in 7.3%, while urinary incontinence, evaluated on a subgroup of total population (4,268 subjects), had a prevalence of 22.3%. During hospitalization (mean stay of 15 days), 74 subjects developed new pressure sores, 55 became fecal and 35 urinary incontinent, and 279 subjects had at least one episode of fall. In multivariate analyses, cognitive impairment, advanced age (85+ years), length of stay (more than 3 weeks) and severe disability were the main independent predictors of development of the four geriatric syndromes, with cognitive impairment as the most significant risk factor for all the four outcomes (OR 4.9, 95% CI 2.4–9.9 for pressure sores; OR 6.3, 95% CI 3.0–13.0 for fecal incontinence; OR 5.3, 95% CI 2.3–12.0 for urinary incontinence; OR 1.6, 95% CI 1.2–2.3 for falls). Conclusion: Very old people have a significant increased risk of several geriatric syndromes during the stay in hospital, particularly if it is long and they are cognitively impaired. A standardized comprehensive geriatric evaluation at admission could be helpful in detecting all subjects at risk and preventing the development of hospital-acquired geriatric syndromes.
Opposite relationship between circulating soluble CD14 concentration and endothelial function in diabetic and nondiabetic subjects
Authors: López-Bermejo Abel , Castro Antoni , Broch Montserrat , Peñarroja Georgina , Vendrell Joan , Vázquez Gabriel , Ricart Wifredo , Fernández-Real José-Manuel
Published: August 2005

Recent prospective studies indicate endothelial dysfunction and increased risk for cardiovascular events in patients with serological evidence of multiple infections. Soluble CD14 (sCD14) plays a key role in the neutralization of lipopolysaccharide (LPS), a well-established bacterial product inducing endothelial dysfunction. Insulin resistance was recently identified as a significant factor influencing circulating sCD14 concentration. Thus, we investigated the association of circulating sCD14 and endothelial dysfunction in subjects with well-established insulin resistance (patients with type 2 diabetes, n=40) compared to control nondiabetic subjects (n=100). To further explore the underlying mechanisms, we also analysed C-reactive protein and circulating NO2-/NO3- and cyclic GMP in the diabetic group. Serum sCD14 concentration (ELISA) was found to be differently associated with endothelium-dependent vasodilatation (EDVD, high-resolution ultrasound) in diabetic and non-diabetic subjects. In nondiabetic subjects, serum sCD14 and C-reactive protein correlated negatively with EDVD (r= −0.21, p=0.03, and r=−0.21, p=0.03, respectively). In a partial correlation analysis, these associations remained significant after controlling for age and weight (sCD14 and EDVD, r=−0.23, p=0.023; C-reactive protein and EDVD, r=−0.21, p=0.03; sCD14 and C-reactive protein, r=0.30, p=0.002). In contrast, sCD14 was positively associated with EDVD in type 2 diabetic patients (r= 0.37, p=0.019,). Interestingly, sCD14 was also associated with NO2-/NO3- in this group (r=0.62, p=0.001, n=22). EDVD also correlated with cyclic GMP (r=0.47, p=0.03, n=22). In summary, circulating sCD14 is associated with endothelial function. While in non-diabetic subjects sCD14 behaves as an acute phase reactant, its role in type 2 diabetic patients should be further clarified. These findings need to be confirmed in further studies with larger number of patients.
Domain 5 of cleaved high molecular weight kininogen inhibits endothelial cell migration through Akt
Authors: Katkade Vaibhav , Soyombo Abigail A. , Isordia-Salas Irma , Bradford Harlan N. , Gaughan John P. , Colman Robert W. , Panetti Tracee S.
Published: August 2005

Domain 5 (D5) of cleaved high molecular weight kininogen (HKa) inhibits angiogenesis in vivo and endothelial cell migration in vitro, but the cell signaling pathways involved in HKa and D5 inhibition of endothelial cell migration are incompletely delineated. This study examines the mechanism of HKa and D5 inhibition of two potent stimulators of endothelial cell migration, sphingosine 1-phosphate (S1P) and vascular endothelial growth factor (VEGF), that act through the PI3-kinase-Akt signaling pathway. HKa and D5 inhibit bovine pulmonary artery endothelial cell (BPAE) or human umbilical vein endothelial cell chemotaxis in the modified-Boyden chamber in response to VEGF or S1P. The inhibition of migration by HKa is reversed by antibodies to urokinase-type plasminogen activator receptor. Both HKa and D5 decrease the speed of BPAE cell migration and alter the morphology in live, time-lapse microscopy after stimulation with S1P or VEGF. HKa and D5 reduce the localization of paxillin to the focal adhesions after S1P and VEGF stimulation. To better understand the intracellular signaling pathways, we examined the effect of HKa on the phosphorylation of Akt and its downstream effector, GSK-3α.HKa and D5 inhibit phosphorylation of Akt and GSK-3α after stimulation withVEGF and S1P. Inhibitors of Akt and PI3-kinase, the upstream activator of Akt, block endothelial cell migration and disrupt paxillin localization to the focal adhesions after stimulation with VEGF and S1P. Therefore we suggest that HKa through its D5 domain alters PI3-kinase- Akt signaling to inhibit endothelial cell migration through alterations in the focal adhesions.
CpG methylation of the PAI-1 gene 5’-flanking region is inversely correlated with PAI-1 mRNA levels in human cell lines
Authors: Skeldal Sune , Krogdahl Annelise , Sørensen Jens Ahm , Andreasen Peter A. , Gao Shan
Published: August 2005

The physiological and pathophysiological functions of PAI-1 are related to its expression by specific cell types in normal and diseased tissues. We analysed the contribution of DNA methylation to the variation in PAI-1 mRNA levels in five cell lines. We found varying frequencies of methylation of 25 CpGs in the -805/+152 region of the PAI-1 gene in Bowes, MCF-7 and U937 cells, while little or no methylation was detected in Hep2 and HT-1080 cells. The methylation frequency was inversely correlated with PAI-1 mRNA level within its 20-fold range in Bowes, MCF-7,U937,and Hep2 cells, while the lack of methylation in both Hep2 and HT- 1080 cells suggested another mechanism behind the 150-fold higher level in HT-1080 cells than in Hep2 cells. However, all cell lines exhibited a high frequency of methylation of 10 CpGs in a CpG island at about -1800. Treatment with 5-aza-2‘-deoxycytidine led up to circa a 40-fold increase in the PAI-1 mRNA level and a strong decrease in the frequency of methylation in the -805/+152 region in Bowes, MCF-7 and U937. The histone deacetylase inhibitor trichostatin A induced a several fold increase of the PAI-1 mRNA level in cells with a high methylation frequency of the -805/+152 region. As compared with matched normal tissue, three samples of oral squamous cell carcinomas displayed decreased frequencies of methylation of the PAI-1 5' flanking region and increased levels of PAI-1 mRNA. These results for the first time implicate DNA methylation and histone acetylation in regulation of the PAI-1 gene, and indicate that without proper CpG islands in 5’-flanking region, trancription may be regulated by methylation of less dense CpGs in the 5’-flanking region rather than methylation of upstream CpG island.
Explicit Filtering and Reconstruction Turbulence Modeling for Large-Eddy Simulation of Neutral Boundary Layer Flow
Authors: Chow Fotini Katopodes , Street Robert L. , Xue Ming , Ferziger Joel H.
Published: August 2005

Standard turbulence closures for large-eddy simulations of atmospheric flow based on finite-difference or finite-volume codes use eddy-viscosity models and hence ignore the contribution of the resolved subfilter-scale stresses. These eddy-viscosity closures are unable to produce the expected logarithmic region near the surface in neutral boundary layer flows. Here, explicit filtering and reconstruction are used to improve the representation of the resolvable subfilter-scale (RSFS) stresses, and a dynamic eddy-viscosity model is used for the subgrid-scale (SGS) stresses. Combining reconstruction and eddy-viscosity models yields a sophisticated (and higher order) version of the well-known mixed model of Bardina et al.; the explicit filtering and reconstruction procedures clearly delineate the contribution of the RSFS and SGS motions. A near-wall stress model is implemented to supplement the turbulence models and account for the stress induced by filtering near a solid boundary as well as the effect of the large grid aspect ratio. Results for neutral boundary layer flow over a rough wall using the combined dynamic reconstruction model and the near-wall stress model show excellent agreement with similarity theory logarithmic velocity profiles, a significant improvement over standard eddy-viscosity closures. Stress profiles also exhibit the expected pattern with increased reconstruction level.
Cyclogenetic Perturbations and Analysis Errors Decomposed into Singular Vectors
Authors: Snyder Chris , Hakim Gregory J.
Published: August 2005

Singular vectors (SVs) have been applied to cyclogenesis, to initializing ensemble forecasts, and in predictability studies. Ideally, the calculation of the SVs would employ the analysis error covariance norm at the initial time or, in the case of cyclogenesis, a norm based on the statistics of initial perturbations, but the energy norm is often used as a more practical substitute.

To illustrate the roles of the choice of norm and the vertical structure of initial perturbations, an upper-level wave with no potential vorticity perturbation in the troposphere is considered as a typical cyclogenetic perturbation or analysis error, and this perturbation is then decomposed by its projection onto each energy SV. All calculations are made, for simplicity, in the context of the quasigeostrophic Eady model (i.e., for a background flow with constant vertical shear and horizontal temperature gradient). Viewed in terms of the energy SVs, the smooth vertical structure of the typical perturbation, as well as its evolution, results from strong cancellation between the growing and decaying SVs, most of which are highly structured and tilted in the vertical.

A simpler picture, involving less cancellation, follows from decomposition of the typical perturbation into SVs using an alternative initial norm, which is based on the relation between initial norms and the statistics of initial perturbations together with the empirical assumption that the initial perturbations are not dominated by interior potential vorticity. Differences between the energy SVs and those based on the alternative initial norm can be understood by noting that the energy norm implicitly assumes initial perturbations with second-order statistics given by the covariance matrix whose inverse defines the energy norm. Unlike the “typical” perturbation, perturbations with those statistics have large variance of potential vorticity in the troposphere and fine vertical structure.

Finally, a brief assessment is presented of the extent to which the upper wave, and more generally the alternative initial norm, is representative of cyclogenetic perturbations and analysis errors. There is substantial evidence supporting deep perturbations with little vertical structure as frequent precursors to cyclogenesis, but surrogates for analysis errors are less conclusive: operational midlatitude analysis differences have vertical structure similar to that of the perturbations implied by the energy norm, while short-range forecast errors and analysis errors from assimilation experiments with simulated observations are more consistent with the alternative norm.
A Large-Eddy Simulation Study of Anisotropy in Fair-Weather Cumulus Cloud Fields
Authors: Hinkelman Laura M. , Stevens Bjorn , Evans K. Franklin
Published: August 2005

Causes of anisotropy in fair-weather cumulus cloud fields were investigated using quantitative measures of anisotropy and a large-eddy simulation (LES) model. Case six of the Global Energy and Water Cycle Experiment (GEWEX) Cloud System Study Working Group 1 was used as the standard model scenario. This case represents radiatively forced development of cumulus clouds over the southern Great Plains. Cloud formation under a variety of environmental conditions was simulated and the degree of anisotropy in the output fields was calculated as a function of spatial scale. Wind shear was found to be the single greatest factor in the development of both vertically tilted and horizontally stretched cloud structures. Other factors included mean wind speed, initial water vapor mixing ratio, and the magnitude of the surface forcing.
The Impact of Zonal Propagation and Seeding on the Eddy–Mean Flow Equilibrium of a Zonally Varying Two-Layer Model
Authors: Zurita-Gotor Pablo , Chang Edmund K. M.
Published: August 2005

This paper investigates the role of zonal propagation for the equilibration of zonally varying flow. It is hypothesized that there exist two ideal limits, for very small or very large group speed. In the first limit the eddies equilibrate locally with the forcing, while in the second limit the equilibration can only be understood in a global sense. To understand these two limits and to assess which is more relevant for the extratropical troposphere, a series of idealized experiments that involves changing the magnitude of the uniform zonal wind is performed. The results of the idealized model experiments suggest that the actual troposphere is likely to be in a transition regime between the two limits, but perhaps closer to the global than the local limit.

Near the global limit, both the eddy amplitude and local baroclinicity over the baroclinic zone are strongly affected by the amount of upstream seeding. When the propagation speed is reduced relative to the control run, the zonal mean eddy activity decreases because the residence time increases more over the stable part of the channel than along the baroclinic zone. With the decrease in upstream seeding, the local supercriticality along the baroclinic zone increases, although the increase is moderate. The decrease in seeding and increase in baroclinicity partially offset the effects of each other, leading to only small changes in the maximum eddy amplitude downstream of the baroclinic zone.

Changes in upstream seeding can also be achieved by enhanced damping. When the eddies are locally damped, the baroclinicity is also enhanced downstream of the damping region due to reduced eddy fluxes. For typical parameters, the recovery of the eddy amplitude occurs over very long distances. Based on these idealized results, it is argued that the coexistence of enhanced baroclinicity and weaker eddy amplitude over the Pacific storm track, as compared to the Atlantic storm track, is consistent with the effects of strong eddy damping over Asia.
A Polarized Delta-Four-Stream Approximation for Infrared and Microwave Radiative Transfer: Part I
Authors: Liou K. N. , Ou S. C. , Takano Y. , Liu Q.
Published: August 2005

The delta-four-stream polarized (vector) thermal radiative transfer has been formulated and numerically tested specifically for application to satellite data assimilation in cloudy atmospheres. It is shown that for thermal emission in the earth’s atmosphere, the [I, Q] component of the Stokes vector can be decoupled from the [U, V] component and that the solution of the vector equation set involving the four-stream approximation can be expressed in an analytic form similar to the scalar case. Thus, the computer time requirement can be optimized for the simulation of forward radiances and their derivatives. Computations have been carried out to illustrate the accuracy and efficiency of this method by comparing radiance and polarization results to those computed from the exact doubling method for radiative transfer for a number of thermal infrared and microwave frequencies. Excellent agreement within 1% is shown for the radiance results for all satellite viewing angles and cloud optical depths. For polarization, differences between the two are less than 5% if brightness temperature is used in the analysis. On balance of the computational speed and accuracy, the four-stream approximation for radiative transfer appears to be an attractive means for the simulation of cloudy radiances and polarization for research and data assimilation purposes.
A Stochastic Model for the Angular Momentum Budget of Latitude Belts
Authors: Egger Joseph
Published: August 2005

The stochastic model of Weickmann et al. for the global angular momentum budget is modified to become applicable to latitude belts. In particular, a Langevin equation is added for the flux divergence of angular momentum in a belt. The friction torque Tf is assumed to be purely damping with respect to angular momentum M. The mountain torque To is generated by red noise but also damps angular momentum directly as suggested by recent stochastic models. The model parameters are tuned such that the variances of all model variables come close to the observations. The corresponding equations for the covariance functions of all variables are solved analytically. The results are compared to observations for selected belts. It is found that the model captures the observed decay rates of all covariance functions. The covariance of the flux divergence and the angular momentum is simulated successfully for positive lags but rarely for negative ones. The covariance of friction torque and angular momentum is reproduced reasonably well. The model is also successful with respect to the covariance of mountain torque and M in the Tropics, but there are large discrepancies at midlatitudes because the observed mountain torque events are accompanied by flux divergences in these belts.
The Vorticity–Velocity Gradient Cofactor Tensor and the Material Invariant of the Semigeostrophic Theory
Authors: Viúdez Álvaro
Published: August 2005

A new derivation and interpretation of the semigeostrophic (SG) material invariant in the theory of geophysical flows is introduced. First, a generalized three-dimensional equation of the SG dynamics is established and the generalized equations for the rate of change of vorticity and for the rate of change of the velocity gradient cofactor tensor are obtained. Next, a conservation equation for the vorticity–velocity gradient cofactor tensor (denoted Ξ̃) is derived. The specific potential Ξ̃, that is, Ξ̃ in the reference configuration per unit of mass, is defined and an expression for its rate of change is obtained. The SG invariant is interpreted as the vertical component of the specific potential Ξ̃. Under the SG assumptions (advection of the geostrophic velocity, hydrostatic, and f-plane approximations) this vertical component is materially conserved in the SG flow. The generalized SG invariant (i.e., the specific potential Ξ̃) differs conceptually from the Beltrami–Rossby–Ertel specific potential vorticity. Its conservation in the SG flow seems to be highly dependent on the SG assumptions, especially on the f-plane approximation and on the horizontal nature of the geostrophic velocity.
Shear Instability in a Shallow Water Model with Implications for the Venus Atmosphere
Authors: Iga Shin-ichi , Matsuda Yoshihisa
Published: August 2005

The shear instability problem in the spherical shallow water system is investigated for three types of wind profiles that are observed at the upper cloud level in Venus. Destabilized Kelvin modes are obtained for all profiles, even when the wind profile is barotropically and inertially stable. The eigenfunctions of these unstable modes are a hybrid of Kelvin modes and continuous modes, which have singularity at the critical latitude. Destabilized Rossby–Kelvin modes are also obtained for the barotropically unstable profile with strong jets. When Lamb parameter ε = (2aΩ)2/gH is large, together with other destabilized gravity modes, these modes have the property of inertial instability modes, which are described by preceding studies on the tropical inertial instability. The destabilizing mechanism of unstable modes is described using resonance theory.

It is found that the angular-momentum flux is equatorward for almost all growing modes obtained in this study; this result is consistent with what the resonance theory predicts. This momentum transport may contribute to the mechanism of producing the superrotation of the Venus atmosphere based on the meridional circulation. The destabilized Kelvin modes may be considered as a source of the 4-day waves observed in the equatorial region at the cloud top of Venus.
Diagnosed Three-Dimensional Axisymmetric Structure of the Mulhall Tornado on 3 May 1999
Authors: Lee Wen-Chau , Wurman Joshua
Published: August 2005

On 3 May 1999, an unusually large tornado that caused F4-level damage and killed several people was intercepted by the Doppler on Wheels (DOW) mobile radar near Mulhall, Oklahoma, from a range of 4 to 9 km, resulting in high-resolution volumetric data every 55 s up to 1.5-km altitude over a period of 14 min. For the first time, the evolution and three-dimensional structure of a tornado were deduced using the ground-based velocity track display (GBVTD) technique. After the circulation center was determined, the tangential wind and radial wind were derived from the GBVTD technique at each radius and height. In addition, the axisymmetric vertical velocity, angular momentum, vorticity, and perturbation pressure were deduced from the tangential and radial wind fields. This study focuses on the axisymmetric aspects of this tornado.

The primary circulation of the Mulhall tornado consisted of an 84 m s−1 peak axisymmetric tangential wind with the radius of maximum wind (RMW) ranging from 500 to 1000 m. The secondary circulation exhibited a two-cell structure characterized by a central downdraft surrounded by an annular updraft near the RMW. The calculated maximum pressure deficit from a 3-km radius to the tornado center at 50-m altitude was −80 hPa. The maximum vorticity during the first 8 min of observation was located inside the RMW away from the tornado center. This vorticity profile satisfied the necessary condition of barotropic instability. As the tornado weakened afterward, the vorticity monotonically increased toward the center. The computed swirl ratios were between 2 and 6, consistent with the observed multiple vortex radar signatures and the vorticity pattern. Swirl ratios were generally smaller during the weakening phase.
Collision Rates of Cloud Droplets in Turbulent Flow
Authors: Franklin Charmaine N. , Vaillancourt Paul A. , Yau M. K. , Bartello Peter
Published: August 2005

Direct numerical simulations of an evolving turbulent flow field have been performed to explore how turbulence affects the motion and collisions of cloud droplets. Large numbers of droplets are tracked through the flow field and their positions, velocities, and collision rates have been found to depend on the eddy dissipation rate of turbulent kinetic energy. The radial distribution function, which is a measure of the preferential concentration of droplets, increases with eddy dissipation rate. When droplets are clustered there is an increased probability of finding two droplets closely separated; thus, there is an increase in the collision kernel. For the flow fields explored in this study, the clustering effect accounts for an increase in the collision kernel of 8%–42%, as compared to the gravitational collision kernel. The spherical collision kernel is also a function of the radial relative velocities among droplets and these velocities increase from 1.008 to 1.488 times the corresponding gravitational value. For an eddy dissipation rate of about 100 cm2 s−3, the turbulent collision kernel is 1.06 times the magnitude of the gravitational value, while for an eddy dissipation rate of 1500 cm2 s−3, this increases to 2.08 times. Therefore, these results demonstrate that turbulence could play an important role in the broadening and evolution of the droplet size distribution and the onset of precipitation.
Convective Structures in a Cold Air Outbreak over Lake Michigan during Lake-ICE
Authors: Zurn-Birkhimer Suzanne M. , Agee Ernest M. , Sorbjan Zbigniew
Published: August 2005

The Lake-Induced Convection Experiment provided special field data during a westerly flow cold air outbreak (CAO) on 13 January 1998, which has afforded the opportunity to examine in detail an evolving convective boundary layer. Vertical cross sections prepared from these data, extending from upstream over Wisconsin out across Lake Michigan, show the modifying effects of land–water contrast on boundary layer mixing, entrainment, heating, and moisture flux. Through this analysis, an interesting case of lake-effect airmass modification was discovered. The data show atypical differing heights in vertical mixing of heat and moisture, as well as offshore downwelling and subsidence effects in the atmosphere. Analysis shows evidence of a new observational feature, the moisture internal boundary layer (MIBL) that accords well with the often recognized thermal internal boundary layer (TIBL). The “interfacial” layer over the lake is also found to be unusually thick and moist, due in part to the upstream conditions over Wisconsin as well as the effectiveness of vertical mixing of moist plumes over the lake (also seen in the aircraft datasets presented). Results show that the atmosphere can be much more effective in the vertical mixing of moisture than heat or momentum (which mixed the same), and thus represents a significant departure from the classical bottom-up and top-down mixing formulation.

Four scales of coherent structures (CSs) with differing spatial and temporal dimensions have been identified. The CSs grow in a building block fashion with buoyancy as the dominating physical mechanism for organizing the convection (even in the presence of substantial wind shear). Characteristic turbulence statistics from aircraft measurements show evidence of these multiple scales of CSs, ranging from the smallest (microscale) in the cloud-free path region near the Wisconsin shore, to the largest (mesoscale) in the snow-filled boundary layer near the Michigan shore.

A large eddy simulation (LES) model has also been employed to study the effects of buoyancy and shear on the convective structures in lake-effect boundary layers. The model simulation results have been divided into two parts: 1) the general relationship of surface heat flux versus wind shear, which shows the interplay and dominance of these two competing forcing mechanisms for establishing convection patterns and geometry (i.e., rolls versus cells), and 2) a case study simulation of convection analogous to the CSs seen in the CFP region for the 13 January 1998 CAO event. Model simulations also show, under proper conditions of surface heating and wind shear, the simultaneous occurrence of differing scales of CSs and at different heights, including both cells and rolls and their coexisting patterns (based on the interplay between the effects of buoyancy and shear).
A Conceptual Model for Entrainment in Cumulus Clouds
Authors: Agrawal Amit
Published: August 2005

Cumulus clouds are generally modeled as a plume, and the model works well up until the cloud base is encountered, beyond which the continuously entraining model does not appear appropriate. Although it has been known for a long time that cumulus clouds have very little lateral entrainment, the reason for it is not evident. An expression for the mean streamwise velocity profile as a Gaussian multiplied by a fourth-order polynomial factor is hereby proposed such that the mass and momentum fluxes are decoupled. This model suggests that cumulus clouds differ from other shear flows in that the former need not interact with the ambient for some downstream distance. The proposed model replicates a number of characteristics of cumulus clouds like a conserved mass flux with varying momentum flux, and may therefore be employed to describe them, in a time-averaged sense, beyond the cloud base.
High-Resolution Satellite Measurements of the Atmospheric Boundary Layer Response to SST Variations along the Agulhas Return Current
Authors: O’Neill Larry W. , Chelton Dudley B. , Esbensen Steven K. , Wentz Frank J.
Published: August 2005

The marine atmospheric boundary layer (MABL) response to sea surface temperature (SST) perturbations with wavelengths shorter than 30° longitude by 10° latitude along the Agulhas Return Current (ARC) is described from the first year of SST and cloud liquid water (CLW) measurements from the Advanced Microwave Scanning Radiometer (AMSR) on the Earth Observing System (EOS) Aqua satellite and surface wind stress measurements from the QuikSCAT scatterometer. AMSR measurements of SST at a resolution of 58 km considerably improves upon a previous analysis that used the Reynolds SST analyses, which underestimate the short-scale SST gradient magnitude over the ARC region by more than a factor of 5. The AMSR SST data thus provide the first quantitatively accurate depiction of the SST-induced MABL response along the ARC. Warm (cold) SST perturbations produce positive (negative) wind stress magnitude perturbations, leading to short-scale perturbations in the wind stress curl and divergence fields that are linearly related to the crosswind and downwind components of the SST gradient, respectively. The magnitudes of the curl and divergence responses vary seasonally and spatially with a response nearly twice as strong during the winter than during the summer along a zonal band between 40° and 50°S. These seasonal variations closely correspond to seasonal and spatial variability of large-scale MABL stability and surface sensible heat flux estimated from NCEP reanalysis fields. SST-induced deepening of the MABL over warm water is evident in AMSR measurements of CLW. Typical annual mean differences in cloud thickness between cold and warm SST perturbations are estimated to be about 300 m.
One-Dimensional CCA and SVD, and Their Relationship to Regression Maps
Authors: Widmann Martin
Published: August 2005

The canonical correlation analysis (CCA) and singular value decomposition (SVD) approaches for estimating a time series from a time-dependent vector and vice versa are investigated, and their relationship to multiple linear regression (MLR) and to regression maps is discussed. Earlier findings are reviewed and combined with new aspects to provide a systematic overview. It is shown that regression maps are proportional to canonical patterns and to singular vectors and that the estimate of a time-dependent vector from a time series does not depend on whether CCA, SVD, or component-wise regressions are used. When a time series is linearly estimated from a time-dependent vector, it is known that CCA is equivalent to MLR. It is demonstrated that an estimate for the time series based on a time expansion coefficient of the regression map that is calculated by orthogonal projection is identical to an SVD estimate, but different from the CCA and MLR estimate. The two approaches also lead to different correlations between the time series and the time expansion coefficient of its signal.

The CCA–MLR and the SVD–regression map approaches are compared in an example where the January Arctic Oscillation index for the period 1948–2002 was estimated from extratropical Northern Hemispheric 850-hPa temperature. For CCA–MLR the leading principal components (PCs) of the temperature field were used as predictors, while for SVD the full field was employed. For more than seven retained PCs the skill in terms of correlations and mean squared error based on cross validation was for both approaches practically identical, but CCA–MLR showed a higher bias. For a smaller number of predictor PCs the SVD–regression map approach performed better. The discrepancy between the skill on the fitting data and on the independent data used for validation was in this example larger for the CCA–MLR approach.
Rainfall Components: Variability and Spatial Distribution in a Mediterranean Area (Valencia Region)
Authors: Millán M. M. , Estrela M. J. , Miró J.
Published: August 2005

In the last half of the twentieth century, the precipitation regime on the Spanish east coast showed an overall pattern of reduction in precipitation totals. This work presents the results from a novel procedure to disaggregate the precipitation series in the Valencia region on the basis of their meteorological origin. Important differences are found between specific trends and changes in the contributions from 1) Atlantic frontal systems, 2) convective–orographic storms, and 3) easterly advections over the Mediterranean Sea (backdoor cold fronts). The series for the three components are then used to analyze the evolution, variability, and spatial distribution of the region’s rainfall and to determine the correlations with the North Atlantic Oscillation (NAO) index. The results establish significant differences between inland areas, with a trend toward decreasing precipitation and thus increasing aridity, and coastal areas, with increasing precipitation that tends to be progressively more torrential in nature. Likewise, the correlations with the NAO index also change and show opposite signs for the different components.
Arctic Surface, Cloud, and Radiation Properties Based on the AVHRR Polar Pathfinder Dataset. Part I: Spatial and Temporal Characteristics
Authors: Wang Xuanji , Key Jeffrey R.
Published: August 2005

With broad spectral coverage and high spatial and temporal resolutions, satellite sensors can provide the data needed for the analysis of spatial and temporal variations of climate parameters in data-sparse regions such as the Arctic and Antarctic. The newly available Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder (APP) dataset was used to retrieve cloud fraction, cloud optical depth, cloud particle phase and size, cloud-top pressure and temperature, surface skin temperature, surface broadband albedo, radiative fluxes, and cloud forcing over the Arctic Ocean and surrounding landmasses for the 18-yr period from 1982 to 1999. In the Arctic, Greenland is the coldest region with the highest surface albedo, while northeastern Russia has the highest surface temperature in summer. Arctic annual mean cloud coverage is about 70%, with the largest cloudiness occurring in September and the lowest cloudiness occurring in April. On annual average, Arctic cloud visible optical depth is about 5–6. Arctic precipitable water is near 0.2 cm in winter and 1.5 cm in summer. The largest downwelling shortwave radiative flux at the surface occurs in June; the largest upwelling shortwave radiative flux occurs in May. The largest downwelling and upwelling longwave radiative fluxes as well as the net all-wave radiative flux occur in July, with the largest loss of longwave radiation from the surface in April.
Knee Stability after Articulated External Fixation
Authors: Fitzpatrick Daniel C. , Sommers Mark B. , Kam Benjamin C. C. , Marsh J. Lawrence , Bottlang Michael
Published: August 2005

Background

Articulated external fixation has been proposed as a method to protect ligament reconstructions while allowing aggressive and early postoperative rehabilitation after knee dislocation. However, the ability of these fixators to protect and stabilize the knee joint has not been clearly determined.

Hypothesis

Articulated external fixation can reduce anteroposterior translation in the cruciate-deficient knee and reduce cruciate ligament strain in cases of intact or reconstructed ligaments.

Study Design

Controlled laboratory study.

Methods

Knee stability was assessed by 3 standard clinical stability tests (Lachman, anterior drawer, and posterior drawer) on 7 human cadaveric lower extremities. Instrumented forces of 100 N were applied to the tibia to measure cruciate ligament forces and tibiofemoral displacement in intact and cruciate-deficient specimens with and without articulated external fixation to determine the degree to which a fixator can protect cruciate ligaments and stabilize the knee. Articulated external fixation was applied using monolateral and bilateral fixators to comparatively analyze the effectiveness of each construct. Statistical analysis was performed using 2-tailed, paired Student t tests.

Results

Application of the monolateral articulated external fixator to specimens with intact ligaments significantly reduced cruciate ligament forces by 1.0 N (P =. 011), 1.7 N (P =. 046), and 1.4 N (P =. 009) for Lachman, anterior drawer, and posterior drawer tests, respectively. In the cruciate ligament-deficient knees, the application of a monolateral fixator significantly reduced tibiofemoral translation by 49%, 70%, and 46% for Lachman, anterior drawer, and posterior drawer tests, respectively. No significant differences between the monolateral and bilateral fixator frames, in terms of ligament protection and joint stabilization, were observed.

Conclusion and Clinical Relevance

Articulated external fixation of the knee can reduce stress in the cruciate ligaments after multiligament reconstructions and can decrease anteroposterior translation in the cruciate-deficient knee.
Autologous Chondrocyte Implantation versus Debridement for Treatment of Full-Thickness Chondral Defects of the Knee
Authors: Fu Freddie H. , Zurakowski David , Browne Jon E. , Mandelbaum Bert , Erggelet Christoph , Moseley J. Bruce , Anderson Allen F. , Micheli Lyle J.
Published: August 2005

Background

Studies that compare the effectiveness of different cartilage repair treatments are needed to update treatment algorithms.

Hypothesis

Autologous chondrocyte implantation provides greater improvement in overall condition score than does debridement at a minimum of 3 years’ follow-up.

Study Design

Cohort study; Level of evidence, 3.

Methods

Cohorts for debridement and autologous chondrocyte implantation each included 58 Cartilage Repair Registry patients who met study criteria. A retrospective analysis was performed on prospectively collected baseline and follow-up data.

Results

Patients in the autologous chondrocyte implantation and debridement groups had similar demographics and chondral lesions at baseline. However, more autologous chondrocyte implantation patients failed a previous debridement or marrow stimulation procedure than did debridement patients. Follow-up outcome assessments were completed by 54 autologous chondrocyte implantation patients and 42 debridement patients. Eighty-one percent of the autologous chondrocyte implantation patients and 60% of the debridement patients reported median improvements of 5 points and 2 points, respectively, in the overall condition score. Autologous chondrocyte implantation patients also reported greater improvements in the median pain and swelling scores than did debridement patients. The treatment failure rate was the same for both autologous chondrocyte implantation and debridement patients. Eighteen autologous chondrocyte implantation patients and 1 debridement patient had at least 1 subsequent operation.

Conclusion

Although patients treated with debridement for symptomatic, large, focal, chondral defects of the distal femur had some functional improvement at follow-up, patients who received autologous chondrocyte implantations obtained higher levels of knee function and had greater relief from pain and swelling at 3 years.