bluuebunny/crossref_metadata_2025 huggingface dataset:
Blockade of HERG human K+channels andIKrof guinea‐pig cardiomyocytes by the antipsychotic drug clozapine
Authors: Lee So‐Young , Kim Young‐Jin , Kim Kyong‐Tai , Choe Han , Jo Su‐Hyun
Published: April 2006

Clozapine, a commonly used antipsychotic drug, can induce QT prolongation, which may lead totorsades de pointesand sudden death. To investigate the arrhythmogenic side effects of clozapine, we studied the impact of clozapine on humanether‐a‐go‐go‐related gene (HERG) channels expressed inXenopusoocytes and HEK293 cells, and on the delayed rectifier K+currents of guinea‐pig cardiomyocytes.

Clozapine dose‐dependently decreased the amplitudes of the currents at the end of voltage steps, and the tail currents of HERG. The IC50for the clozapine blockade of HERG currents inXenopusoocytes progressively decreased relative to depolarization (39.9 μMat −40 mV, 28.3 μMat 0 mV and 22.9 μMat +40 mV), whereas the IC50for the clozapine‐induced blockade of HERG currents in HEK293 cells at 36°C was 2.5 μMat +20 mV.

The clozapine‐induced blockade of HERG currents was time dependent: the fractional current was 0.903 of the control at the beginning of the pulse, but declined to 0.412 after 4 s at a test potential of 0 mV.

The clozapine‐induced blockade of HERG currents was use‐dependent, exhibiting more rapid onset and greater steady state blockade at higher frequencies of activation, with a partial relief of blockade observed when the frequency of activation was decreased.

In guinea‐pig ventricular myocytes held at 36°C, treatment with 1 and 5 μMclozapine blocked the rapidly activating delayed rectifier K+current (IKr) by 24.7 and 79.6%, respectively, but did not significantly block the slowly activating delayed rectifier K+current (IKs).

Our findings collectively suggest that blockade of HERG currents andIKr, but notIKs, may contribute to the arrhythmogenic side effects of clozapine.

British Journal of Pharmacology(2006)148, 499–509. doi:10.1038/sj.bjp.0706744
Band gap creation using quasiordered structures based on sonic crystals
Authors: Romero-García V. , Fuster E. , García-Raffi L. M. , Sánchez-Pérez E. A. , Sopena M. , Llinares J. , Sánchez-Pérez J. V.
Published: April 2006

It is well known that sonic crystals are periodic structures that present acoustic band gaps attenuation centered at frequencies related with the lattice constant of the structure. We present an approach based on genetic algorithms to create band gaps in a predetermined range of frequencies. The mechanism used by genetic algorithms to achieve this objective is the creation of vacancies in a starting sonic crystal, built with air-embedded rigid scatterers. As a result of the optimization process, we obtain quasiordered structures on which acoustic properties are based in the multiple scattering theory.
The Light Peak of the Electroretinogram Is Dependent on Voltage-gated Calcium Channels and Antagonized by Bestrophin (Best-1)
Authors: Marmorstein Lihua Y. , Wu Jiang , McLaughlin Precious , Yocom John , Karl Mike O. , Neussert Rudgar , Wimmers Soenke , Stanton J. Brett , Gregg Ronald G. , Strauss Olaf , Peachey Neal S. , Marmorstein Alan D.
Published: April 2006

Mutations in VMD2, encoding bestrophin (best-1), cause Best vitelliform macular dystrophy (BMD), adult-onset vitelliform macular dystrophy (AVMD), and autosomal dominant vitreoretinochoroidopathy (ADVIRC). BMD is distinguished from AVMD by a diminished electrooculogram light peak (LP) in the absence of changes in the flash electroretinogram. Although the LP is thought to be generated by best-1, we find enhanced LP luminance responsiveness with normal amplitude in Vmd2−/− mice and no differences in cellular Cl− currents in comparison to Vmd2+/+ littermates. The putative Ca2+ sensitivity of best-1, and our recent observation that best-1 alters the kinetics of voltage-dependent Ca2+ channels (VDCC), led us to examine the role of VDCCs in the LP. Nimodipine diminished the LP, leading us to survey VDCC β-subunit mutant mice. Lethargic mice, which harbor a loss of function mutation in the β4 subunit of VDCCs, exhibited a significant shift in LP luminance response, establishing a role for Ca2+ in LP generation. When stimulated with ATP, which increases [Ca++]I, retinal pigment epithelial cells derived from Vmd2−/− mice exhibited a fivefold greater response than Vmd2+/+ littermates, indicating that best-1 can suppress the rise in [Ca2+]I associated with the LP. We conclude that VDCCs regulated by a β4 subunit are required to generate the LP and that best-1 antagonizes the LP luminance response potentially via its ability to modulate VDCC function. Furthermore, we suggest that the loss of vision associated with BMD is not caused by the same pathologic process as the diminished LP, but rather is caused by as yet unidentified effects of best-1 on other cellular processes.
Relationship between Pore Occupancy and Gating in BK Potassium Channels
Authors: Piskorowski Rebecca A. , Aldrich Richard W.
Published: April 2006

Permeant ions can have significant effects on ion channel conformational changes. To further understand the relationship between ion occupancy and gating conformational changes, we have studied macroscopic and single-channel gating of BK potassium channels with different permeant monovalent cations. While the slopes of the conductance–voltage curve were reduced with respect to potassium for all permeant ions, BK channels required stronger depolarization to open only when thallium was the permeant ion. Thallium also slowed the activation and deactivation kinetics. Both the change in kinetics and the shift in the GV curve were dependent on the thallium passing through the permeation pathway, as well as on the concentration of thallium. There was a decrease in the mean open time and an increase in the number of short flicker closing events with thallium as the permeating ion. Mean closed durations were unaffected. Application of previously established allosteric gating models indicated that thallium specifically alters the opening and closing transition of the channel and does not alter the calcium activation or voltage activation pathways. Addition of a closed flicker state into the allosteric model can account for the effect of thallium on gating. Consideration of the thallium concentration dependence of the gating effects suggests that the flicker state may correspond to the collapsed selectivity filter seen in crystal structures of the KcsA potassium channel under the condition of low permeant ion concentration.
Predicting severity of haemophilia A and B splicing mutations by information analysis
Authors: VON KODOLITSCH Y. , BERGER J. , ROGAN P. K.
Published: April 2006

Summary.  Bleeding symptoms and clotting activity vary among mutations that alter mRNA splicing of either the factor VIII or factor IX genes. We analyzed splicing mutations in both genes for changes in individual information (Ri, in bits) involving both donor or acceptor sites. Mutations with low or negative Ri values (<2.4 bits) or significant changes in Ri (ΔRi ≥ 7 bits) exhibited either reduced protein activity, increased clotting time and bleeding frequency and were predictive of severe disease. Thus, information analysis of splicing mutations may be useful in predicting phenotypes in hemophilia.
Insight into molecular changes of the FIX protein in a series of Italian patients with haemophilia B
Authors: BICOCCHI M. P. , PASINO M. , ROSANO C. , MOLINARI A. C. , VALLE E. DELLA , LANZA T. , BOTTINI F. , ACQUILA M.
Published: April 2006

Summary.  Deficiency or dysfunction of factor IX FIX leads to haemophilia B (HB), an X‐linked, recessive, bleeding disorder. On a molecular basis, HB is due to a heterogeneous spectrum of mutations spread throughout the F9 gene. In several instances, a cause‐effect relation has been elucidated, in others predicted possibilities have been offered by crystallography inspection and by software‐constructed models of the protein. The aim of this study was to contribute to the understanding of HB molecular pathology. The F9 missense mutations we identified in 21 unrelated Italian HB patients by direct sequencing of the whole F9 coding regions were inspected for the causative effect they provoked on the ensuing transcript, and on the protein structure. Each alteration was studied in order to: (i) characterize the defect on the basis of the nature of the mutation; (ii) identify the predicted defect that is induced in the gene and (iii) speculate about the potential, detrimental effects which upset the protein functionality through an idealized FIX model. The resulting data may further contribute to the comprehension of the mechanisms underlying the disease.
A comparison of stainless steel Flexofiles and nickel‐titanium NiTiFlex files during the shaping of simulated canals
Authors: BISHOP K. , DUMMER P. M. H.
Published: April 2006

The aim of this study was to compare the shaping ability of stainless steel Flexofiles and nickel‐titanium NiTiFlex files during the preparation of simulated canals in resin blocks. A total of 80 canals with various angles and position of curvature were prepared by one operator using either Flexofiles or NiTiFlex files in a modified double‐flared technique with balanced force method of instrument manipulation. Canal shape was assessed at two stages during the procedure, after apical enlargement to size 30 and subsequently at size 45. Pre‐ and post‐operative images of the canals, were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre‐ and post‐operative views. Canal preparation using NiTiFlex files was significantly quicker (P<0.0001) up to size 30. More instrument failures occurred with Flexofiles (12) compared to NiTiFlex files (7) but there were no statistically significant differences between file type, instrument size or canal shape. Flexofiles created significantly more zips, perforations and ledges; there were no differences in terms of danger zones. Overall, canals prepared with Flexofiles were significantly wider because more material was removed from the outer aspect of the curve at the end‐point of preparation and from the inner aspect of the curve at the apex. Under the conditions of this study, preparation with NiTiFlex files was more effective and produced more appropriate canal shapes than Flexofiles.
Inducible and endothelial nitric oxide synthase genes polymorphism in inflammatory bowel disease
Authors: Oliver J. , Gómez‐Garcia M. , Vilchez J. R. , López‐Nevot M. Á. , Piñero A. , Correro F. , Nieto A. , Martín J.
Published: April 2006

To assess the influence of inducible and endothelial nitric oxide synthase gene (NOS2A and NOS3) polymorphisms in susceptibility to Crohn's disease (CD) and ulcerative colitis (UC). A total of 505 inflammatory bowel disease (IBD) patients (221 with UC and 284 with CD) and 332 ethnically matched controls were studied. Patients and controls were genotyped by polymerase chain reaction ‐based techniques for a multiallelic (CCTTT)n repeat and biallelic marker (TAAA)n in the promoter region of the NOS2A gene and for a T/C polymorphism at position −786 in the promoter region and a polymorphism in exon 7(298Glu/Asp) of the NOS3 gene. There was not association between NOS2A and NOS3 genotypes, alleles or haplotypes frequencies with UC, CD and controls. Our data suggest that NOS2A and NOS3 polymorphisms do not play a major role in IBD predisposition.
Why a Multinational Firm Chooses Expatriates: Integrating Resource‐Based, Agency and Transaction Costs Perspectives*
Authors: Tan Danchi , Mahoney J. T.
Published: April 2006

abstract This paper develops an integrative organizational economics framework explaining and predicting multinational firms' managerial resource deployments based on resource‐based, agency, and transaction costs theories. Our empirical findings suggest that the governance decision for managerial services of multinational firms is influenced not only by the comparative capabilities of managers, but also by the economic costs to the firm of influencing the behaviours of managers through managerial contracting.
Limits to Communities of Practice
Authors: Roberts Joanne
Published: April 2006

abstract  The purpose of this paper is to critically explore the communities of practice approach to managing knowledge and its use among management academics and practitioners in recent years. In so doing, the aim is to identify the limits of the approach in the field of knowledge management. The paper begins with a brief description of the communities of practice approach. This is followed by a review of critiques of the approach evident in the management literature. A number of further challenges are then elaborated. The limits of communities of practice are subsequently discussed and brief conclusions drawn.
A POST‐KEYNESIAN AMENDMENT TO THE NEW CONSENSUS ON MONETARY POLICY
Authors: Lavoie Marc
Published: April 2006

A common view is now pervasive in policy research at universities and central banks, which one could call the New Keynesian consensus, based on an endogenous money supply. This new consensus reproduces received wisdom: in the long run, expansionary fiscal policy leads to higher inflation rates and real interest rates, while more restrictive monetary policy only leads to lower inflation rates. The paper provides a simple four‐quadrant apparatus to represent the above, and it shows that simple modifications to the new consensus model are enough to radically modify received doctrine as to the likely effects of fiscal and monetary policies.
RISK‐AVERSION, OPTIMAL LEVERAGE AND THE INVESTMENT–UNCERTAINTY RELATION
Authors: Femminis Gianluca
Published: April 2006

We develop a partial equilibrium dynamic model in which firms are risk‐averse. We analyse the determinants of the investment–uncertainty relationship by means of numerical techniques. When firms can borrow ‘outside’ resources at the riskless rate, an increase in price volatility depresses investment for realistic parameter values. In our model, portfolio considerations play an important role. When the marginal revenue of capital becomes more uncertain, the risk‐averse firm's owners reduce their ‘short position’ in the risk‐free asset, thus diminishing the firm's debt level. The contraction in leverage reduces the expected returns on investment because the expected marginal revenue product is higher than the user cost of capital. In turn, the reduction in expected yields tends to depress investment.
The Wealth Effect on New Business Startups in a Developing Economy
Authors: MESNARD ALICE , RAVALLION MARTIN
Published: April 2006

The paper tests for nonlinearities in the wealth effect on self‐employment, as can arise from startup costs or liquidity constraints. Using both nonparametric and parametric methods, we show that the relationship between the probability of a return migrant to Tunisia starting up a business and the stock of his savings repatriated at return is concave for almost the entire range of our data, though we find weak evidence of a convex relationship at very low wealth levels. Our results suggest that the aggregate self‐employment rate is an increasing function of aggregate wealth, but a decreasing function of wealth inequality.
The E‐Correspondence Principle
Authors: EVANS GEORGE W. , HONKAPOHJA SEPPO
Published: April 2006

We present a new application of Samuelson's Correspondence Principle to the analysis of comparative dynamics in stochastic rational expectations models. Our version, which we call the E‐correspondence principle, applies to rational expectations equilibria that are stable under least squares and closely related learning rules. With this technique it is sometimes possible to study, without explicitly solving for the equilibrium, how qualitative properties of the equilibrium are affected by changes in the model parameters. Applications to overlapping generations and New Keynesian models illustrate the potential of the technique.
General obstetrics: Preterm birth and multiple pregnancy in European countries participating in the PERISTAT project
Authors: Blondel B , Macfarlane A , Gissler M , Breart G , Zeitlin J
Published: April 2006

Objective  To compare rates of preterm birth among multiple births in European countries, to estimate their contribution to overall preterm birth rates and to explore factors which could explain differences between preterm birth rates.

Design  Analyses of data from vital statistics, birth registers or national samples of births.

Setting  Eleven member states of the European Union.

Population  All live births or representative samples of births at national or regional level for the year 2000 or most recent year.

Methods  Description of rates of preterm birth before 37 and 32 weeks, estimation of population attributable risks (PAR), study of associations between preterm birth rates in multiples and singletons and nonspontaneous labour using Spearman's rank correlation coefficient.

Main outcome measures  Preterm birth rates, PAR, proportions of deliveries with nonspontaneous onset (caesarean sections before labour or induction of labour).

Results  The proportion of multiple births before 37 weeks varied from 68.4% in Austria to 42.2% in the Republic of Ireland. In half of the countries, over 20% of all preterm births were attributable to multiple births. A strong association was found between the proportions of births before 37 weeks among multiple and singleton births (r= 0.81; P < 0.001). An association was observed between the rates of preterm birth and the proportions of deliveries with nonspontaneous onset among twins.

Conclusions  Wide variations in rates of preterm births and deliveries with nonspontaneous onset were found between countries, suggesting marked differences in clinical practice which could have long‐term implications for the health of children from multiple births.
Transgenics and Vertebrate Cloning as Tools for Species Conservation
Authors: EHRENFELD DAVID
Published: April 2006

Abstract: It has been suggested that transgenics and vertebrate cloning have a role to play in conservation. Now is the time to evaluate their risks and benefits, before these technologies are widely implemented in our field. Direct risks of transgenics include escape and introgression of transgenes into wild populations; weedy invasion by transgenic organisms; toxicity or pathogenicity of engineered organisms and their products; and human error in the field testing and tracking of transgenic organisms. Indirect risks include environmental effects of increased herbicide use; the danger that engineered organisms may aid the development of bioweapons; the likelihood that gene patenting will lead to the privatization of natural resources; and the diversion of support from less glamorous forms of conservation. Formal risk assessments are commonly used to evaluate transgenic procedures, but our incomplete understanding of both ecosystem processes and the action of transgenes renders most of these assessments scientifically and socially unjustified. Nevertheless, a few, low‐risk applications of transgenics may be possible: for example, “super‐sterile” ornamental cultivars. Vertebrate cloning poses little risk to the environment, but it can consume scarce conservation resources, and its chances of success in preserving species seem poor. To date, the conservation benefits of transgenics and vertebrate cloning remain entirely theoretical, but many of the risks are known and documented. Conservation biologists should devote their research and energies to the established methods of conservation, none of which require transgenics or vertebrate cloning.
How Corridors Reduce Indigo Bunting Nest Success
Authors: WELDON AIMEE J.
Published: April 2006

Abstract:  Corridors are a popular strategy to conserve biodiversity and promote gene flow in fragmented landscapes. Corridor effectiveness has been bolstered by the fact that no empirical field studies have shown negative effects on populations or communities. I tested the hypothesis that corridors increase nest predation in connected habitat fragments relative to unconnected fragments. I evaluated this hypothesis in a large‐scale experimental system of open‐habitat fragments that varied in shape and connectivity. Corridors increased nest predation rates in connected fragments relative to unconnected fragments with lower edge:area ratios. Nest predation rates were similar between connected and unconnected fragments with higher edge:area ratios. These results suggest that the increase in predator activity is largely attributable to edge effects incurred through the addition of a corridor. This is the first field study to demonstrate that corridors can negatively impact animal populations occupying connected fragments.
Detecting Biodiversity Hotspots by Species‐Area Relationships: a Case Study of Mediterranean Beetles
Authors: FATTORINI SIMONE
Published: April 2006

Abstract:  Any method of identifying hotspots should take into account the effect of area on species richness. I examined the importance of the species‐area relationship in determining tenebrionid (Coleoptera: Tenebrionidae) hotspots on the Aegean Islands (Greece). Thirty‐two islands and 170 taxa (species and subspecies) were included in this study. I tested several species‐area relationship models with linear and nonlinear regressions, including power, exponential, negative exponential, logistic, Gompertz, Weibull, Lomolino, and He‐Legendre functions. Islands with positive residuals were identified as hotspots. I also analyzed the values of the C parameter of the power function and the simple species‐area ratios. Species richness was significantly correlated with island area for all models. The power function model was the most convenient one. Most functions, however, identified certain islands as hotspots. The importance of endemics in insular biotas should be evaluated carefully because they are of high conservation concern. The simple use of the species‐area relationship can be problematic when areas with no endemics are included. Therefore the importance of endemics should be evaluated according to different methods, such as percentages, to take into account different levels of endemism and different kinds of “endemics” (e.g., endemic to single islands vs. endemic to the archipelago). Because the species‐area relationship is a key pattern in ecology, my findings can be applied at broader scales.
Are you Talking to Me? The Nature of Community in Entrepreneurship Scholarship
Authors: Gartner William B. , Davidsson Per , Zahra Shaker A.
Published: April 2006

This special issue is devoted to understanding the scientific structure of entrepreneurship research. Research in entrepreneurship has grown rapidly, encompassing multiple theoretical and methodological traditions. Articles in this issue use bibliometric techniques to find linkages among published entrepreneurship scholars. These analyses show that research in the entrepreneurship field contains: multiple but disconnected themes; dominant themes that reflect the disciplinary training and lens of their authors; and considerable dynamism and change in key research themes over time. These special issue articles provide rich opportunities for identifying insightful, influential, and creative research niches in the entrepreneurship field.
Influence of angiogenesis inhibitors on endothelial cell morphology in vitro
Authors: FRIIS TINA , HANSEN ALASTAIR B. , HOUEN GUNNAR , ENGEL ANNE‐MARIE
Published: April 2006

Human umbilical vein endothelial cells (HUVEC) propagated in co‐culture with fibroblasts form capillary‐like networks of tubes. Here we characterize the morphology and ultrastructure of HUVEC in such co‐cultures and investigate the influence of different angiogenesis inhibitors on endothelial cell morphology. Addition of angiogenesis inhibitors to the co‐culture disrupted endothelial network formation and influenced endothelial cell morphology in two distinct ways. Instead of characteristic capillary‐like networks, the endothelial cell morphology appeared as either short cords or compact cell clusters of variable size. Electron microscopy (EM) showed that in co‐culture untreated HUVEC formed capillary‐like tubes with lumina and retained important ultrastructural and physiological properties of endothelial cells in functional vessels as they contained both Weibel‐Palade bodies and transport vesicles. Immuno‐EM showed that the endothelial cell marker CD 31 stained endothelial membranes at cell‐cell contacts, and at the luminal and abluminal side of the capillary‐like tubes, although most abundantly at the luminal membranes. No ultrastructural signs of apoptosis were seen in HUVEC in inhibitor‐treated co‐cultures. Our results demonstrate that treatment with levamisole or anti‐VEGF inhibits endothelial cell differentiation into tubes or instead induces formation of compact endothelial cell clusters. Treatment with platelet factor 4, suramin and TNP‐470 results in formation of short endothelial cell cords. We discuss the implications of these findings.
The Pitch Rise Paradigm: A New Task for Real-Time Endoscopy of Non-Stationary Phonation
Authors: Rasp Oliver , Lohscheller Jörg , Doellinger Michael , Eysholdt Ulrich , Hoppe Ulrich
Published: April 2006

As standard stroboscopy is restricted to the recording of periodic vocal fold vibrations, observations of non-stationary laryngeal mechanisms demand real-time recording systems, the most advanced being the high-speed video technique. It allows the registration of laryngeal parameters during a variation of the fundamental frequency. The aim of this study was to compare amplitude and frequency parameters of vocal fold vibration during stationary and non-stationary phonation, i.e. a monotonous pitch rise. Twenty-nine young female adults with no incidence of voice disorders were examined while performing two different phonation tasks: sustained phonation with a constant frequency and a monotonous pitch rise. Endoscopic recordings and the acoustic signals were acquired simultaneously. Both acoustic and laryngeal parameters were derived for short time intervals of 17.8 ms for the constant pitch and pitch rise conditions. Instantaneous frequency, sound pressure level, vibratory amplitudes of the vocal folds and the type of glottal closure were compared. At the beginning of the pitch rise, the acoustic and laryngeal parameters were similar to the parameters that occurred within the sustained phonation conditions. In contrast, the laryngeal parameters at the middle and at the end of the pitch rise differed substantially from those during sustained phonation. For the first time, quantitative measures of the growing glottal chink and the vibration amplitude decrease during pitch increase could be taken. In general, the image evaluation of the pitch rise paradigm can be subdivided into the starting, the raising and the final phase. As each phase can be considered as quasi-stationary, existing software modules are capable of analysing the process by treating each phase separately. Hence, the pitch rise condition may be suitable for clinical examination to detect information of voice disturbances that cannot be visualized during sustained phonation.
The Influence of Utterance Position on Children’s Production of Lexical Stress
Authors: Smith Allan B. , Robb Michael P.
Published: April 2006

Previous studies reporting acoustical data on children’s production of lexical stress examined words produced in isolation (i.e., with no carrier phrase) or in utterance-final position. In such contexts, the final syllable of the words being examined was also the utterance-final syllable. Syllables produced in utterance-final position are known to be longer in duration and lower in intensity and F₀ compared to other syllables within utterances. Therefore, utterance-final effects may have obscured previous results on children’s production of stress. Twenty children at approximately 6 years of age produced novel trochaic and iambic words in utterance-final and utterance-non-final position. Comparing productions across the two utterance positions suggested that reliance upon the utterance-final context was a confounding factor in past studies. Utterance-final position facilitated the iambic pattern of duration (short-long) and the trochaic pattern of intensity and F₀ (high-low). Utterance position sometimes affected trochees differently than iambs, especially in the duration of word-final syllables. The results are discussed in terms of past explanations of utterance position effects on acoustic characteristics of syllables.
Can Predialysis Hypertension Prevent Intradialytic Hypotension in Hemodialysis Patients?
Authors: Takeda Atsushi , Toda Takayuki , Fujii Takuma , Sasaki Sei , Matsui Noriaki
Published: April 2006

Background/Aim: Intradialytic hypotension is the most common complication associated with hemodialysis, and its cause is multifactorial. However, the relationship between hypertension and intradialytic hypotension is not clear. We investigated the influence of predialysis blood pressure and antihypertensive drugs on intradialytic hypotension. Methods: Risk factors for intradialytic hypotension were analyzed in 111 patients undergoing regular hemodialysis treatment and had annual echocardiography performed. The correlation between the addition of antihypertensive medications and the incidence of intradialytic hypotensive episodes was studied in 21 hypertensive patients. Results: Based on multivariate logistic regression analysis, diabetes (odds ratio OR 8.18, 95% confidence interval CI 1.47–45.5; p = 0.016), interdialytic weight gain (OR 2.45, 95% CI 1.24–4.82; p = 0.010), ejection fraction (OR 0.88, 95% CI 0.81–0.95; p = 0.001), and left ventricular volume (OR 0.97, 95% CI 0.94–0.99; p = 0.013) were determined as risk factors for intradialytic hypotension. However, there was no association between predialysis blood pressure and intradialytic hypotension. After additional antihypertensive medications, the predialysis blood pressure fell from 175/85 mm Hg to 154/78 mm Hg (p < 0.0001/p < 0.0001). The mean 24-hour interdialytic blood pressure fell from 165/87 mm Hg to 147/80 mm Hg (p < 0.0001/p = 0.006). However, the frequency of hypotensive episodes was not increased (p = 0.77). Conclusions: Diabetes, excessive interdialytic weight gain, low ejection fraction, and low left ventricular volume are independent risk factors for intradialytic hypotension. However, no correlation was found between predialysis blood pressure values or addition of antihypertensive medications and the incidence of intradialytic hypotension. Thus, hypertension may be controlled without aggravating intradialytic hypotension in hemodialysis patients.
Multiresolution Analysis of Radiative Transfer through Inhomogeneous Media. Part II: Validation and New Insights
Authors: Ferlay Nicolas , Isaka Harumi , Gabriel Philip , Benassi Albert
Published: April 2006

The multiresolution radiative transfer equations of Part I of this paper are solved numerically for the case of inhomogeneous model clouds using Meyer’s basis functions. After analyzing the properties of Meyer’s connection coefficients and effective coupling operators (ECOs) for two examples of extinction functions, the present approach is validated by comparisons with Spherical Harmonic Discrete Ordinate Method (SHDOM) and Monte Carlo codes, and a preliminary analysis of the local-scale coupling between the cloud inhomogeneities and the radiance fields is presented. It is demonstrated that the contribution of subpixel-scale cloud inhomogeneities to pixel-scale radiation fields may be very important and that it varies considerably as a function of local cloud inhomogeneities.
Effects of Upper-Level Shear on the Structure and Maintenance of Strong Quasi-Linear Mesoscale Convective Systems
Authors: Coniglio Michael C. , Stensrud David J. , Wicker Louis J.
Published: April 2006

Recent observational studies have shown that strong midlatitude mesoscale convective systems (MCSs) tend to decay as they move into environments with less instability and smaller deep-layer vertical wind shear. These observed shear profiles that contain significant upper-level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong, long-lived convective systems in some past idealized simulations. Thus, to explore the role of upper-level shear in strong MCS environments, a set of two-dimensional (2D) simulations of density currents within a dry, statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper-level shear. A set of three-dimensional (3D) simulations of MCSs is produced to gauge the effects of the upper-level shear in a more realistic framework.

Results from the 2D experiments show that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface. Parcels that are elevated above the surface (1–2 km) overturn and are responsible for the deep lifting in the deep-shear environments, while the surface-based parcels typically are lifted through the cold pool region in a rearward-sloping path. This deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3D simulations, even in the presence of 3D structures. These results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude MCSs.
Statistics of Absolute and Relative Dispersion in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study
Authors: Dosio Alessandro , de Arellano Jordi Vilà-Guerau
Published: April 2006

The influence of the different scales of turbulent motion on plume dispersion in the atmospheric convective boundary layer (CBL) is studied by means of a large-eddy simulation (LES). In particular, the large-scale (meandering) and small-scale (relative diffusion) contributions are separated by analyzing dispersion in two reference systems: the absolute (fixed) coordinate system and the coordinate system relative to the plume’s instantaneous center of mass. In the relative coordinate system, the (vertically) inhomogeneous meandering motion is removed, and only the small-scale, homogeneous turbulent motion contributes to the dispersion process.

First, mean plume position, dispersion parameters (variance), and skewness of the plume position are discussed. The analysis of the third-order moments shows how the structure and the symmetry of scalar distribution are affected with respect to the turbulent characteristics of the CBL (inhomogeneity of the large-scale vertical motion) and the presence of the boundary conditions (surface and top of the CBL). In fact, the reflection of the plume by the CBL boundaries generates the presence of nonlinear cross-correlation terms in the balance equation for the third-order moments of the plume position. As a result, the third-order moment of the absolute position is not balanced by the sum of the third-order moments of the meandering and relative plume position.

Second, mean concentration and concentration fluctuations are calculated and discussed in both coordinate systems. The intensity of relative concentration fluctuation icr, which quantifies the internal (in plume) mixing, is explicitly calculated. Based on these results, a parameterization for the probability distribution function (PDF) of the relative concentration is proposed, showing very good agreement with the LES results. Finally, the validity of Gifford’s formula, which relates the absolute concentration’s high-order moments to the relative concentration and the PDF of the plume centerline, is studied. It is found that due to the presence of the CBL boundaries, Gifford’s formula is not able to reproduce correctly the value of the absolute mean concentration near the ground. This result is analyzed by showing that, when the plume is reflected by the CBL boundaries, the instantaneous relative plume width z′2r(t) departs from its mean value σ2r. By introducing the skewness of the relative plume position into a parameterization for the relative mean concentration, the results for the calculated mean concentration are improved.
The Meridional Flow of Source-Driven Abyssal Currents in a Stratified Basin with Topography. Part I: Model Development and Dynamical Properties
Authors: Swaters Gordon E.
Published: April 2006

The equatorward flow of source-driven grounded deep western boundary currents within a stratified basin with variable topography is examined. The model is the two-layer quasigeostrophic (QG) equations, describing the overlying ocean, coupled to the finite-amplitude planetary geostrophic (PG) equations, describing the abyssal layer, on a midlatitude β plane. The model retains subapproximations such as classical Stommel–Arons theory, the Nof abyssal dynamical balance, the so-called planetary shock wave balance (describing the finite-amplitude β-induced westward propagation of abyssal anomalies), and baroclinic instability. The abyssal height field can possess groundings. In the reduced gravity limit, a new nonlinear steady-state balance is identified that connects source-driven equatorward abyssal flow (as predicted by Stommel–Arons theory) and the inertial topographically steered deep flow described by Nof dynamics. This model is solved explicitly, and the meridional structure of the predicted grounded abyssal flow is described. In the fully baroclinic limit, a variational principle is established and is exploited to obtain general stability conditions for meridional abyssal flow over variable topography on a β plane. The baroclinic coupling of the PG abyssal layer with the QG overlying ocean eliminates the ultraviolet catastrophe known to occur in inviscid PG reduced gravity models. The baroclinic instability problem for a constant-velocity meridional abyssal current flowing over sloping topography with β present is solved and the stability characteristics are described.
The Retrieval of Asymmetric Tropical Cyclone Structures Using Doppler Radar Simulations and Observations with the Extended GBVTD Technique
Authors: Liou Yu-Chieng , Wang Tai-Chi Chen , Lee Wen-Chau , Chang Ya-Ju
Published: April 2006

The ground-based velocity track display (GBVTD) technique is extended to two Doppler radars to retrieve the structure of a tropical cyclone’s (TC’s) circulation. With this extension, it is found that the asymmetric part of the TC radial wind component can be derived up to its angular wavenumber-1 structure, and the accuracy of the retrieved TC tangential wind component can be further improved. Although two radar systems are used, a comparison with the traditional dual-Doppler synthesis indicates that this extended GBVTD (EGBVTD) approach is able to estimate more of the TC circulation when there are missing data. Previous research along with this study reveals that the existence of strong asymmetric radial flows can degrade the quality of the GBVTD-derived wind fields. When a TC is observed by one radar, it is suggested that the GBVTD method be applied to TCs over a flat surface (e.g., the ocean) where the assumption of relatively smaller asymmetric radial winds than asymmetric tangential winds is more likely to be true. However, when a TC is observed by two radar systems, especially when the topographic effects are expected to be significant, the EGBVTD rather than the traditional dual-Doppler synthesis should be used.

The feasibility of the proposed EGBVTD method is demonstrated by applying it to an idealized TC circulation model as well as a real case study. Finally, the possibility of combining EGBVTD with other observational instruments, such as dropsonde or wind profilers, to recover the asymmetric TC radial flow structures with even higher wavenumbers is discussed.
The Role of Shearwise and Transverse Quasigeostrophic Vertical Motions in the Midlatitude Cyclone Life Cycle
Authors: Martin Jonathan E.
Published: April 2006

The total quasigeostrophic (QG) vertical motion field is partitioned into transverse and shearwise couplets oriented parallel to, and along, the geostrophic vertical shear, respectively. The physical role played by each of these components of vertical motion in the midlatitude cyclone life cycle is then illustrated by examination of the life cycles of two recently observed cyclones.

The analysis suggests that the origin and subsequent intensification of the lower-tropospheric cyclone responds predominantly to column stretching associated with the updraft portion of the shearwise QG vertical motion, which displays a single, dominant, middle-tropospheric couplet at all stages of the cyclone life cycle. The transverse QG omega, associated with the cyclones’ frontal zones, appears only after those frontal zones have been established. The absence of transverse ascent maxima and associated column stretching in the vicinity of the surface cyclone center suggests that the transverse ω plays little role in the initial development stage of the storms examined here. Near the end of the mature stage of the life cycle, however, in what appears to be a characteristic distribution, a transverse ascent maximum along the western edge of the warm frontal zone becomes superimposed with the shearwise ascent maximum that fuels continued cyclogenesis.

It is suggested that use of the shearwise/transverse diagnostic approach may provide new and/or supporting insight regarding a number of synoptic processes including the development of upper-level jet/front systems and the nature of the physical distinction between type A and type B cyclogenesis events.
Digital Filter Initialization for MM5
Authors: Chen Min , Huang Xiang-Yu
Published: April 2006

In this paper several configurations of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5), which is implemented at Beijing Institute of Urban Meteorology in China, are used to demonstrate the initial noise problem caused either by interpolating global model fields onto an MM5 grid or by using MM5 objective analysis schemes. An implementation of a digital filter initialization (DFI) package to MM5 is then documented. A heavy rain case study and intermittent data assimilation experiments are used to assess the impact of DFI on MM5 forecasts. It is shown that DFI effectively filters out the noise and produces a balanced initial model state. It is also shown that DFI improves the spinup aspects for precipitation, leading to better scores for short-range precipitation forecasts. The issues related to the initialization of variables that are not observed and/or analyzed, in particular those for nonhydrostatic quantities, are discussed.
Educational Policy and Reform for Homeless Students
Authors: Mawhinney-Rhoads Lynnette , Stahler Gerald
Published: April 2006

This article provides an overview of educational reform efforts that have been targeted toward assisting homeless students. The authors first review some of the difficulties and barriers that confront homeless children in terms of school access and academic success. The authors then examine four different types of educational reforms for homeless students—mainstreamed schools, supplemental supports, transitional schools (separate schools), and modified comprehensive schools—in relation to the existing barriers for homeless students. Using a case study approach, the authors briefly describe the first modified comprehensive school in the nation and the programs that are being implemented at the school. This article concludes that school reforms for homeless children need to be tailored to the specific context of the community and not be based on national one-size-fits-all reform policy. Recommendations are provided to assist in the planning of educational programs to enhance the academic success of the homeless student.
Educational Attainment and Residential Location
Authors: Sander William
Published: April 2006

The effects of residential location at age 16 and current residential location on measures of educational attainment are estimated. Particular attention is given to the effects of migration and family background on educational outcomes. It is shown that central cities and suburbs of large metropolitan areas in the United States have significantly higher levels of educational attainment. The reasons for this include migration of more highly educated individuals to large metropolitan areas and family background factors that are more favorable to higher levels of educational attainment in large urban areas. It is also shown that although urban advantages in schooling for respondents at age 16 have declined over time, urban advantages for respondents when they are older have increased. Data from the National Opinion Research Center’s General Social Survey are used.
Social networks and the psychological contract: Structural holes, cohesive ties, and beliefs regarding employer obligations
Authors: Ho Violet T. , Rousseau Denise M. , Levesque Laurie L.
Published: April 2006

This study examined the relationship between employees' social network positions and their psychological contract beliefs. In particular, it investigated the relationship of employee advice and friendship ties with their employer's relational (long-term, non-monetizable), balanced (performance-related), and transactional (short-term, monetizable) obligations to them. Data obtained from a start-up research firm showed that employees brokering structural holes in the advice network believed the firm had greater balanced and transactional obligations to them. Employees with cohesive ties in the friendship network also believed that the firm owed them more balanced and transactional obligations. Neither structural holes nor cohesion were related to relational obligations. This study develops implications for psychological contracts and social networks research.
A model of political leadership
Authors: Morrell Kevin , Hartley Jean
Published: April 2006

In this article we develop a model of political leadership. In doing so, we analyse the challenges facing political leaders in local government in England and Wales. We use this analysis as a basis for broader theorizing: about leadership at other levels of government, and in other countries. The scope for applying extant accounts of leadership in these domains can be enhanced by considering the relational complexities that characterize the environment within which political leaders act; by doing so we offer an agenda for research. We describe the context for political leaders in terms of figurational sociology, where figurations denote interdependent networks of social relations. These take shape in different arenas of action, and are partly influenced by the different roles that political leaders undertake. These figurations are also constituted differently given the diversity inherent in the context for enacting political leadership. We propose a conceptual model that serves both as a heuristic framework to organize conceptualization of this understudied area, and to orient future research.