Maximal Dispersion Research Articles

Defining Exercise Synchrony in Fit Young Adults: A Tissue Doppler Study

Exercise-induced changes in the synchrony of left ventricular contraction may be an important therapeutic target in heart failure. There are limited data to support the feasibility of exercise assessments. In addition, the effect of exercise on synchrony in healthy individuals is undetermined. Eleven healthy young men underwent tissue Doppler assessments before and immediately after maximal cardiopulmonary exercise. Left ventricular synchrony was assessed using pulsed wave tissue Doppler of the lateral, septal, inferior, and anterior walls. The maximal dispersion times between the walls for onset and peak systolic velocities were used as synchrony indices. The proportion of the cardiac cycle taken between Q wave and time to onset or peak systolic motion was constant at rest and peak exercise. There was no significant exercise-induced change seen in either interventricular or intraventricular synchrony. Exercise synchrony assessment is technically feasible. Synchronization of cardiac contraction is maintained after maximal exercise in healthy individuals.

Highly hydrophilic and stable polypeptide/single-wall carbon nanotube conjugates

A polymeric dispersing agent for single-wall carbon nanotubes (SWCNTs) in water was synthesized by 4-(pyren-1-yl)butanoylation of the amine groups of poly-L-lysine. The pyrene content of 4-(pyren-1-yl)butanoylated polylysine (PBPL) was optimized so that a maximal dispersion effect of the SWCNTs was obtained. High molecular weight PBPL (>300000 g mol−1) exceeds the widely used surfactant sodium dodecylsulfate (SDS) as a dispersing agent yielding a 27% higher SWCNT concentration in dispersion. The high stability of the PBPL/SWCNT conjugates is demonstrated by removing the conjugates from dispersion through filtration, washing, and redispersion in only water. The resulting redispersions do not contain free PBPL and the importance of having SWCNT dispersions in the absence of free dispersing agent is discussed. For SDS dispersions, poor redispersion properties have been observed. The binding of PBPL onto the SWCNTs was studied by atomic force microscopy, optical absorbance spectroscopy, and fluorescence spectroscopy.

Daily rhythm of aggregation in the haematophagous bug Triatoma infestans (Heteroptera: Reduviidae)

Triatomine bugs show a temporal modulation of many activities. Here, we analyse the daily modulation of the aggregation behaviour of Triatoma infestans larvae and its chronobiological basis. In the laboratory, groups of six bugs were released over an experimental arena during six consecutive days, where their aggregation behaviour was quantified every hour. When submitted to a 12/12 h photoperiod (L/D), the larvae of T. infestans exhibited a cyclic pattern of aggregation with a 24 h period, evincing the existence of a daily rhythm of aggregation in this species. Bugs exhibited the maximum aggregation tendency at the end of the scotophase (7:00 h), moment in which they naturally search for refuges. The minimum aggregation (i.e. maximal dispersion) was observed during the last part of the photophase and beginning of the scotophase (15:00 to 1:00 h). This cyclic pattern disappeared when constant conditions of illumination (L/L) or darkness (D/D) were imposed to the bugs, suggesting the absence of an endogenous circadian control of this behaviour. Insects submitted to L/L and D/D photoperiods presented lower global levels of aggregation than those submitted to L/D conditions. The lack of an endogenous control and the relevance of light cycles as a synchronization signal are discussed as the temporal modulation of this behaviour might play an important role in the nocturnal habits of this species.

Optimal dispersion and central places

This paper presents research into optimal dispersion models as applied to central places. The literature regarding location optimization and central places is reviewed and the motivation for employing dispersion models is identified. Models that employ the objective of maximal dispersion in the context of central places are formulated and solved in the context of both single- and multiple-good systems. Two methods for generating multiple-good systems are presented: a multiple-type dispersion model and a K-value constraint set formulation. Sequential solutions to dispersion models demonstrate how a system of central places could develop over time. The solutions to these models generate the patterns of central places expected under the organizing principles of central place theory. The objective of maximal dispersion is posited as both a motivating factor in central place location decisions, and as the optimal outcome of a mature system of central places.

Cosmic microwave background alignment in multi-connected universes

The low multipoles of the cosmic microwave background (CMB) anisotropy possess some strange properties such as the alignment of the quadrupole and the octopole, and the extreme planarity or the extreme sphericity of some multipoles. In this paper, the CMB anisotropy of several multi-connected space forms is investigated with respect to the maximal angular momentum dispersion and the Maxwellian multipole vectors in order to settle the question of whether such spaces can explain the low multipole anomalies in the CMB. The following spaces are considered: the Picard topology in hyperbolic space, three spherical spaces (Poincaré dodecahedron, binary tetrahedron and binary octahedron) and a hypertorus in flat space. Although these spaces are able to produce the large-scale suppression of the CMB anisotropy, they do not describe the CMB alignment. From the models considered, the Picard universe shows the strongest alignment properties.

Heterogeneous ventricular chamber response to hypokalemia and inward rectifier potassium channel blockade underlies bifurcated T wave in guinea pig

It was previously demonstrated that transmural electrophysiological heterogeneities can inscribe the ECG T wave. However, the bifurcated T wave caused by loss of inward rectifier potassium current (I(K1)) function is not fully explained by transmural heterogeneities. Since right ventricular (RV) guinea pig myocytes have significantly lower I(K1) than left ventricular (LV) myocytes, we hypothesized that the complex ECG can be inscribed by heterogeneous chamber-specific responses to hypokalemia and partial I(K1) blockade. Ratiometric optical action potentials were recorded from the epicardial surface of the RV and LV. BaCl(2) (10 micromol/l) was perfused to partially block I(K1) in isolated guinea pig whole heart preparations. BaCl(2) or hypokalemia alone significantly increased RV basal (RV(B)) action potential duration (APD) by approximately 30% above control compared with LV apical (LV(A)) APD (14%, P<0.05). In the presence of BaCl(2), 2 mmol/l extracellular potassium (hypokalemia) further increased RV(B) APD to a greater extent (31%) than LV(A) APD (19%, P<0.05) compared with BaCl(2) perfusion alone. Maximal dispersion between RV(B) and LV(A) APD increased by 105% (P<0.05), and the QT interval prolonged by 55% (P<0.05) during hypokalemia and BaCl(2). Hypokalemia and BaCl(2) produced an ECG with a double repolarization wave. The first wave (QT1) corresponded to selective depression of apical LV plateau potentials, while the second wave (QT2) corresponded to the latest repolarizing RV(B) myocytes. These data suggest that final repolarization is more sensitive to extracellular potassium changes in regions with reduced I(K1), particularly when I(K1) availability is reduced. Furthermore, underlying I(K1) heterogeneities can potentially contribute to the complex ECG during I(K1) loss of function and hypokalemia.

Effect of design on the performance of a dry powder inhaler using computational fluid dynamics. Part 2: Air inlet size

This study investigates the effect of air inlet size on (i) the flowfield generated in a dry powder inhaler, and (ii) the device-specific resistance, and the subsequent effect on powder deagglomeration. Computational fluid dynamics (CFD) analysis was used to simulate the flowfield generated in an Aerolizer with different air inlet sizes at 30, 45, and 60 l/min. Dispersion performance of the modified inhalers was measured using mannitol powder and a multistage liquid impinger at the same flow rates. The air inlet size had a varying effect on powder dispersion depending on the flow rate. At low flow rates (30 and 45 l/min), reducing the air inlet size increased the inhaler dispersion performance by increasing the flow turbulence and particle impaction velocities above their critical levels for maximal powder dispersion. At 60 l/min, reducing the air inlet size reduced the inhaler dispersion performance by releasing a large amount of powder from the device before the turbulence levels and particle impaction velocities could be fully developed. The results demonstrate that the maximal inhaler dispersion performance can be predicted if details of the device flowfield are known.

Adsorptive Separation of Light Olefin/Paraffin Mixtures

An effective adsorbent for the ethylene/ethane separation has been prepared by the dispersion of CuCl in large NaX crystals. The results from the thermo gravimetric analysis (TGA) indicate a maximal dispersion capacity of 36 wt% of CuCl for the NaX crystals. Single component isotherms of ethane and ethylene on CuCl/NaX show that the CuCl containing adsorbents are highly favourable to the olefin, which is ascribed to the strong interaction due to the formation of π-complexes between ethylene and CuCl. Breakthrough experiments demonstrate that CuCl/NaX can be used as an effective adsorbent for the separation of ethylene and ethane mixtures and would allow the use of more sustainable processes.

Montmorillonite-thermoset nanocomposites via cryo-compounding

For organically modified montmorillonite (OMM)–epoxy nanocomposites, maximal montmorillonite dispersion is found to depend synergistically on the mechanical processing history of the resin mixture and the chemistry at the OMM surface. Specifically, Cloisite 30A (quaternary ammonium OMM) and I30.E (primary ammonium OMM), each containing surfactants with different catalytic effects on the curing chemistry of Epon 862, are compared. Irrespective of the OMM, conventional solvent-free processing methodologies, including sonication, result in an inhomogeneous distribution of OMM on the micron scale. Even though the primary ammonium alkyls within I30.E enhance intragallery reactivity, this only results in extensive swelling of tactoids (interlayer distance ∼10–20nm), and thus retention of layer–layer correlations, leading to ‘hybrid’ micron scale reinforcing particles, not nanoscale dispersion of individual layers. In contrast, sub-ambient temperature (cryo) compounding had substantial impact on the ability to reduce tactoid and agglomerate size and increase homogeneity of dispersion for Cloisite 30A. The reactivity near Cloisite 30A is similar to that in the bulk and thus localized gelation around the layer-stacks does not retard particulate refinement. In all cases, alteration of the global epoxy network structure was ruled out by FTIR and NMR measurements. For nanocomposites with similar OMM content, however, the final thermal–mechanical properties does not coherently relate to one characteristic of the morphology. The coefficient of thermal expansion (T>Tg) and hardness (T<Tg) depend only weakly on morphology, where as the glass transition temperature depends strongly on the extent of OMM dispersion and interfacial chemistry. In general, the inter-relationships between mechanical processing, OMM surface chemistry and the desired property enhancements are not linear and thus must be considered in light of a final application to evaluate the optimal ‘nanocomposite’ fabrication methodology to achieve maximal benefit.

Effect of metal loading and carbon support microstructure on the dispersion of Pt/C catalysts prepared viaadsorption of chloroplatinic acid

Adsorption of H2PtCl6onto a carbon support followed by reduction of the adsorbed platinum species with H2at 250°C leads to Pt/C catalysts, which show universal volcano-like dependence of platinum dispersion on the metal loading in the range from 0.01 to 0.55mmol (Pt)/m2(SBET) when highly disordered carbons, namely, active carbons and carbon blacks, are used as supports. The maximal dispersion D(CO/Pt) = 0.8 is attained at 0.18mmol (Pt)/m2 (SBET). With other factors being equal, the dispersion of platinum supported on carbons with a more regular crystal structure, especially Sibunit-type supports, proves to be the highest and independent of the metal loading.The differences between the two groups of carbon supports are explained by the differences in the state of the adsorbed platinum precursors.

Amplified Transmural Dispersion of Repolarization as the Basis for Arrhythmogenesis in a Canine Ventricular-Wedge Model of Short-QT Syndrome

The short-QT syndrome is a new clinical entity characterized by corrected QT intervals <300 ms and a high incidence of ventricular tachycardia (VT) and fibrillation (VF). Gain-of-function mutations in the gene for outward potassium currents have been shown to underlie the congenital syndrome. The present study examined the cellular basis of VT/VF in an experimental model associated with short QT intervals created with a potassium channel activator. Transmembrane action potentials from epicardial and M regions, 4 transmural unipolar electrograms, and a pseudo-ECG were simultaneously recorded in canine arterially perfused left ventricular wedge preparations. At a basic cycle length of 2000 ms, pinacidil (2 to 3 mumol/L) abbreviated the QT interval from 303.7+/-5.4 to 247.3+/-6.9 ms (mean+/-SEM, P<0.0001). The maximal transmural dispersion of repolarization (TDR(max)) increased from 27.0+/-3.8 to 64.9+/-9.2 ms (P<0.01), and an S2 applied to the endocardium induced a polymorphic VT (pVT) in 9 of 12 wedge preparations (P<0.01). Addition of isoproterenol (100 nmol/L, n=5) led to greater abbreviation of the QT interval, a further increase in TDR(max) (from 55.4+/-13.7 to 69.7+/-8.3 ms), and more enduring pVT. TDR(max) was correlated significantly with the T(peak)-T(end) interval under all conditions. The effects of pinacidil were completely reversed by glybenclamide (10 micromol/L, n=4) and partially reversed by E4031 (5 micromol/L, n=5), which prevented induction of pVT in 3 of 5 preparations. Our data suggest that heterogeneous abbreviation of the action potential duration among different cell types spanning the ventricular wall creates the substrate for the genesis of VT under conditions associated with short QT intervals.

Phonetic properties of three Ayuuk (Mixe-Zoquean) dense vowel systems

Several theories of vowel dispersion have proposed that the vowel systems of languages tend to distribute evenly in the phonetic space to maximize the perceptual distinctness of the vowels (Liljencrants and Lindblom, 1972; Lindblom, 1986; Lindblom and Maddieson, 1988; Schwartz et al., 1997). This study investigates the acoustic properties of three Ayuuk (Mixe) languages spoken in Mexico, possessing dense vocalic systems, which in addition have a series of normal and the corresponding set of long vowels: Santa Mara Ocotepec Ayuuk (SMOA) with nine vowels /i, I, u, e, E, o, A, a, O/, Tlahuitoltepec Ayuuk (TA) with eight vowels /i, I, e, E, o, A, a, O/, and Alotepec Ayuuk (AA) with seven vowels /i, u, e, E, o, a, O/. The inventories of the Ayuuk languages are typologically interesting; the SMOA and AA systems are rather uncommon (Maddiesson, 1984), in contrast with the system of TA, which conforms to the main trends of vowel systems. Preliminary results lend support to a dispersion/focalization hypothesis in that the vowels are evenly dispersed in the available space and remain focalized without significant overlap with adjacent vowels. The phonetic properties analyzed in this paper suggest that two principles, maximal dispersion and maximal distinctness, shape the overall distribution of the vowel inventory of Ayuuk languages.

Electrophysiological and proarrhythmic parameters in transmural canine left-ventricular needle biopsies.

This study was designed to validate the use of small, transmural, left-ventricular biopsies in the dog for investigations of electrophysiological and proarrhythmic properties of the heart. This technique could facilitate pharmacological in vitro testing in remodelled hearts of both man and animal. Small, transmural, semi-cylindrical, left-ventricular biopsies from dogs with normal sinus rhythm (SR) were characterized electrophysiologically and compared with biopsies from electrically remodelled hearts from dogs with chronic, complete AV-block (CAVB). In at least five biopsy segments recordings were made to determine the action potential duration (APD), the transmural gradient of repolarization, the maximal transmural dispersion (deltatM(max)) and presence of early after-depolarizations (EADs) at different pacing cycle lengths (PCLs) in the absence and presence of a class-III agent, ibutilide (10(-6) M). The biopsies showed stable and normal AP characteristics, a conduction velocity of 0.22 +/- 0.05 m/s and normal frequency dependence of the APD. The location of the longest APD varied, thus creating transmural repolarization gradients with differing morphology. Ibutilide prolonged the APD, accentuated repolarization gradients and induced EADs. CAVB biopsies had significantly longer APDs, a larger dispersion of repolarization and showed more EADs in the presence of ibutilide than SR biopsies. We conclude that this biopsy technique provides coherent and valid transmural electrophysiological data in dogs under various conditions.

Fourth-Order Symmetric DIRK Methods for Periodic Stiff Problems

New symmetric DIRK methods specially adapted to the numerical integration of first-order stiff ODE systems with periodic solutions are obtained. Our interest is focused on the dispersion (phase errors) of the dominant components in the numerical oscillations when these methods are applied to the homogeneous linear test model. Based on this homogeneous test model we derive the dispersion conditions for symmetric DIRK methods as well as symmetric stability functions with real poles and maximal dispersion order. Two new fourth-order symmetric methods with four and five stages are obtained. One of the methods is fourth-order dispersive whereas the other method is symplectic and sixth-order dispersive. These methods have been applied to a number of test problems (linear as well as nonlinear) and some numerical results are presented to show their efficiency when they are compared with the symplectic DIRK method derived by Sanz-Serna and Abia (SIAM J. Numer. Anal. 28 (1991) 1081–1096).

Immature-like astrocytes are associated with dentate granule cell migration in human temporal lobe epilepsy

In human temporal lobe epilepsy, a dispersion of dentate granule cells is frequently described in adults who had an early risk factor. To elucidate the role of glia in this phenomenon, we investigated neuronal dispersion, astrocyte organization and expression of intermediate filaments of mature and immature astrocytes (i.e. glial fibrillary acidic protein (GFAP) and vimentin, respectively) in seven subjects with early febrile seizures (F(+)) and five subjects with other etiologies than febrile seizures (F(−)). Compared to F(−) patients, a majority of F(+) subjects showed neuronal dispersion and vimentin expression in radial glia. However, in two patients with the maximal dispersion, radial processes expressed only GFAP. We suggest that granule cell migration that occurs in adult epileptic focus results from the transient occurrence of immature-like glia throughout the granular layer.

Cytoarchitectural abnormalities in hippocampal sclerosis.

Hippocampal sclerosis (HS) is the most common pathological substrate for temporal lobe epilepsy with a characteristic pattern of loss of principle neurons primarily in CA1 and hilar subfields. Other cytoarchitectural abnormalities have been identified in human HS specimens, including dispersion of dentate granule cells and cytoskeletal abnormalities in residual hilar cells. The incidence of these features, their relationship to the severity of HS and potential indication of underlying hippocampal maldevelopment is unverified. In a series of 183 hippocampectomies we identified classical HS (grades 3 and 4) in 90% of specimens, granule cell disorganization or severe dispersion in 40% of cases with a bilaminar pattern in 10%, and cytoskeletal abnormalities in hilar cells in 55% of cases. The severity of granule cell disorganization correlated closely with the degree of hippocampal neuronal loss but not with the age at first seizure or a history of a precipitating event for epilepsy such as prolonged febrile seizures. These findings suggest that granule cell disorganization is closely linked with the progression of HS rather than a hallmark of impaired hippocampal maturation. Furthermore, stereological quantitation of granule cells showed evidence of cell loss but greater numbers in regions of maximal dispersion, which may indicate enhanced neurogenesis of these cells. Quantitation of reelin-and calretinin-positive Cajal-Retzius cells in the dentate gyrus molecular layer in 26 cases showed no correlation between the number of these cells and the severity of granule cell dispersion, but increased numbers of these cells were present in HS with respect to control groups. Although a role for Cajal-Retzius cells is therefore not implicated in the mechanism of granule cell disorganization, their excess number may be indicative of underlying hippocampal maldevelopment in HS.

Dispersion of atrial repolarization in patients with paroxysmal atrial fibrillation.

To study the role of the dispersion of atrial repolarization (DAR) in the genesis of atrial fibrillation (AF), monophasic action potentials (MAP) were recorded simultaneously from a catheter at the high lateral right atrium (HLRA) and a catheter moving around the high, middle and low lateral right atrium (RA) the high, anterior and posterior septal RA and the RA appendage in 15 patients with paroxysmal AF and 15 patients with atrioventricular nodal re-entry tachycardia (AVNRT) or concealed Wolff-Parkinson-White syndrome (WPW) without history of AF. After recordings during sinus rhythm (SR), MAPs were recorded during programmed stimulation (PS) via the HLRA catheter at a drive cycle length (CL) of 500 ms. Thus, MAPs were recorded simultaneously from 2 sites at a time and sequentially from 4 to 12 sites during SR, drive pacing and PS. Taking the MAP at the HLRA as reference, the dispersion of repolarization time (dispersion of RT) and its two components, the dispersions of activation time (dispersion of AT) and MAP duration (dispersion of MAP duration) among the 4 to 12 sites were calculated and taken as parameters of DAR. During SR and PS, the maximal dispersion of RT was significantly greater in AF than in control patients, 113+/-49 ms vs 50+/-28 ms (P<0.001) and 114+/-56 vs 70+/-43 ms (P<0.05) respectively. The increased dispersion of RT in the AF group was caused by increases in both dispersion of MAP duration and dispersion of AT. During SR and PS, DAR increased in patients with paroxysmal AF due to increases in dispersion of MAP duration and dispersion of AT, which suggests the involvement of both repolarization and conduction disturbances in the development of paroxysmal AF.

QT intervals and QT dispersion as measures of left ventricular hypertrophy in an unselected hypertensive population

Electrocardiographic (ECG) QT intervals and dispersion correlate with echocardiographic left ventricular mass index (LVMI) in groups of selected essential hypertensives. We tested the strength of this relationship in a large group of unselected hypertensives to assess whether QT measurements may be a simple screening test for LVH in clinical practice. In a cross-sectional study of 386 unselected hypertensive subjects, maximal QT intervals (QT max), QT dispersion (QT disp), and ECG voltages (Sokolow-Lyon and Cornell sex-specific voltages) were measured from 12-lead ECG. The LVMI correlated most strongly with Cornell voltage (linear regression r = 0.44, P < .001). The strongest relationship between LVMI and QT parameters was with QT max, (r = 0.25, P < .001). This relationship weakened using heart rate-corrected QT max. Correlations between LVMI and QT disp were weak, whether or not they were corrected for heart rate. Sokolow-Lyon voltages, Cornell voltage and QT max, but not QT disp, were independently predictive of LVMI after adjustment for age, sex, race, and the other ECG parameters. Receiver operating characteristic (ROC) curve analyses demonstrated that no QT parameter performed better than simple ECG voltage criteria in the detection of LVH. In conclusion, QT max, the QT parameter most strongly associated with LVMI, was independently associated with LVMI after adjustment for standard ECG voltage criteria. However, as an isolated measure it was no better than simple ECG voltage criteria as a screening test for LVH in clinical practice.

Prolonged QTc interval predicts mortality in patients with Type 1 diabetes mellitus.

To evaluate prolonged QTc interval and QT dispersion as predictors of all-cause and cardiovascular mortality after adjustment for well-established risk factors in Type 1 diabetic patients. From a cohort of all adult Type 1 diabetic patients, duration of diabetes >or= 5 years, attending the clinic in 1984 and followed in an observational study for 10 years (n = 939), all subjects with resting baseline electrocardiograms were identified (n = 697, 360 males). The QT length was measured and corrected for heart rate (QTc). Maximal QTc length (QTc max) and QT dispersion were determined. At baseline, 431 had normoalbuminuria (< 30 mg/24 h), 138 had microalbuminuria (30-299 mg/24 h) and 128 had macroalbuminuria (>or= 300 mg/24 h) of whom 66 (15%), 35 (25%) and 61 (48%) died during follow-up, respectively (26 (6%), 14 (10%), 21 (16%) from cardiovascular disease). QTc max. was 442 (1.2) ms (mean (SEM)) for survivors and 457 (3.7) in patients who died (P < 0.001). In a Cox proportional hazards model including baseline values of putative risk factors, independent predictors of death were QTc max (P = 0.03), age (P < 0.001), presence of hypertension (P = 0.001), male sex (P < 0.001), log urinary albumin excretion (P < 0.001), smoking (P = 0.04), log serum-creatinine (P < 0.001), height (P < 0.001), low social class (P = 0.04), whereas QT dispersion, heart rate, and HbA1c were not included. In the subgroup with macroalbuminuria, but not for all patients, QTc max was an independent risk factor for cardiovascular mortality. QTc prolongation, but not increased QT dispersion, is an independent marker of increased mortality in patients with Type 1 diabetes mellitus.

QT dispersion in microalbuminuric Type 1 diabetic patients without myocardial ischemia

Microalbuminuria is associated with an increased risk of cardiac death. We assessed whether urinary albumin excretion is related to abnormalities of the QT interval independently of myocardial ischemia. Thirty-four patients with type 1 diabetes who were free from ischemic heart disease on the basis of normal stress electrocardiography and echocardiography were studied. Maximal QT interval and dispersion were significantly greater in the group with microalbuminuria ( n=17) compared to controls ( n=17) with normal urinary albumin excretion (394 [26.1] vs. 373.8 [27.8] ms; P=.044 and 62.4 [21.8] vs. 42.7[11.6] arbitrary units; P=.009). Autonomic function was similar between the groups. Urinary albumin excretion correlated positively with QT dispersion ( P=.023). These data suggest that in type 1 diabetic patients, QT abnormalities can occur independently of autonomic dysfunction or myocardial ischemia and may be related to the processes which increase urinary albumin leakage.