Tidal Limitation Research Articles

THE INFLUENCE OF EDAPHIC FACTORS ON THE SCLEROPHYLLY OF MANGROVE TREE SPECIES IN SOUTHERN BRAZIL

Mangroves are coastal ecosystems, subject to limiting environmental conditions and constituted by tree communities. The tree species have adaptations to develop under such stress conditions. The sclerophylly is a response to environments with multiple stresses. In the mangrove forests, these stresses are induced mainly by salinity, frequency of tidal influence, soil waterlogging, and nutrient limitation. The aim of the study was to establish if the degree of sclerophylly, expressed in leaf morphology and nutrient contents in tree species of mangroves is associated with edaphic and salinity conditions. The study was performed in one mangrove at Paraná state, Brazil, where two plots were sampled (fringe and interior). Leaves of 15 individuals of each species (Avicennia schaueriana, Laguncularia racemosa and Rhizophora mangle) for each plot (fringe and interior) were collected for chemical and morphological analysis. Soil samples adjacent to each selected tree were collected to perform fertility analyses. The fringe soils samples present higher carbon and organic matter, C:P ratio, pore water salinity and sand predominance. The specific leaf area (SLA) showed that species have sclerophyllous leaves in different degrees: L. racemosa > R. mangle > A. schaueriana. The different degrees of sclerophylly found among the studied species and among plots indicated that each species has its own strategies and that they manifest themselves distinctly in morphological and physiological terms, even when developing under similar environmental conditions.

Overnight variation in tidal expiratory flow limitation in COPD patients and its correction: an observational study

BackgroundTidal expiratory flow limitation (EFLT) is common among COPD patients. Whether EFLT changes during sleep and can be abolished during home ventilation is not known.MethodsCOPD patients considered for noninvasive ventilation used a ventilator which measured within-breath reactance change at 5 Hz (∆Xrs) and adjusted EPAP settings to abolish EFLT. Participants flow limited (∆Xrs > 2.8) when supine underwent polysomnography (PSG) and were offered home ventilation for 2 weeks. The EPAP pressure that abolished EFLT was measured and compared to that during supine wakefulness. Ventilator adherence and subjective patient perceptions were obtained after home use.ResultsOf 26 patients with supine EFLT, 15 completed overnight PSG and 10 the home study. In single night and 2-week home studies, EFLT within and between participants was highly variable. This was unrelated to sleep stage or body position with only 14.6% of sleep time spent within 1 cmH2O of the awake screening pressure. Over 2 weeks, mean EPAP was almost half the mean maximum EPAP (11.7 vs 6.4 cmH2O respectively). Group mean ∆Xrs was ≤ 2.8 for 77.3% of their home use with a mean time to abolish new EFLT of 5.91 min. Adherence to the ventilator varied between 71 and 100% in prior NIV users and 36–100% for naïve users with most users rating therapy as comfortable.ConclusionsTidal expiratory flow limitation varies significant during sleep in COPD patients. This can be controlled by auto-titrating the amount of EPAP delivered. This approach appears to be practical and well tolerated by patients.Trial registration: The trial was retrospectively registered at CT.gov NCT04725500.

The period-gap cataclysmic variable CzeV404 Her: A link between SW Sex and SU UMa systems

Context. We present a new study of the eclipsing cataclysmic variable CzeV404 Her (Porb = 0.098 d) that is located in the period gap. Aims. This report determines the origin of the object and the system parameters and probes the accretion flow structure of the system. Methods. We conducted simultaneous time-resolved photometric and spectroscopic observations of CzeV404 Her. We applied our light-curve modelling techniques and the Doppler tomography method to determine the system parameters and analyse the structure of the accretion disk. Results. We found that the system has a massive white dwarf MWD = 1.00(2) M⊙, a mass ratio of q = 0.16, and a relatively hot secondary with an effective temperature T2 = 4100(50) K. The system inclination is i = 78.8°. The accretion disk spreads out to the tidal limitation radius and has an extended hot spot or line region. The hot spot or line is hotter than the remaining outer part of the disk in quiescence or in intermediate state, but does not stand out completely from the disk flux in (super)outbursts. Conclusions. We claim that this object represents a link between two distinct classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion flow structure in the disk corresponds to the SW Sex systems, but the physical conditions inside the disk fit the behaviour of SU UMa-type objects.

Effect of nocturnal EPAP titration to abolish tidal expiratory flow limitation in COPD patients with chronic hypercapnia: a randomized, cross-over pilot study

BackgroundTidal expiratory flow limitation (EFLT) promotes intrinsic PEEP (PEEPi) in patients with chronic obstructive pulmonary disease (COPD). Applying non-invasive ventilation (NIV) with an expiratory positive airway pressure (EPAP) matching PEEPi improves gas exchange, reduces work of breathing and ineffective efforts. We aimed to evaluate the effects of a novel NIV mode that continuously adjusts EPAP to the minimum level that abolishes EFLT.MethodsThis prospective, cross-over, open-label study randomized patients to one night of fixed-EPAP and one night of EFLT-abolishing-EPAP. The primary outcome was transcutaneous carbon dioxide pressure (PtcCO2). Secondary outcomes were: peripheral oxygen saturation (SpO2), frequency of ineffective efforts, breathing patterns and oscillatory mechanics.ResultsWe screened 36 patients and included 12 in the analysis (age 72 ± 8 years, FEV1 38 ± 14%Pred). The median EPAP did not differ between the EFLT-abolishing-EPAP and the fixed-EPAP night (median (IQR) = 7.0 (6.0, 8.8) cmH2O during night vs 7.5 (6.5, 10.5) cmH2O, p = 0.365). We found no differences in mean PtcCO2 (44.9 (41.6, 57.2) mmHg vs 54.5 (51.1, 59.0), p = 0.365), the percentage of night time with PtcCO2 > 45 mm Hg was lower (62(8,100)% vs 98(94,100)%, p = 0.031) and ineffective efforts were fewer (126(93,205) vs 261(205,351) events/hour, p = 0.003) during the EFLT-abolishing-EPAP than during the fixed-EPAP night. We found no differences in oxygen saturation and lung mechanics between nights.ConclusionAn adaptive ventilation mode targeted to abolish EFLT has the potential to reduce hypercapnia and ineffective efforts in stable COPD patients receiving nocturnal NIV.Trial registration: ClicalTrials.gov, NCT04497090. Registered 29 July 2020—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04497090.

Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse.

Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.

Kinematical evolution of tidally limited star clusters: the role of retrograde stellar orbits

The presence of an external tidal field often induces significant dynamical evolutionary effects on the internal kinematics of star clusters. Previous studies investigating the restricted three-body problem with applications to star cluster dynamics have shown that unbound stars on retrograde orbits (with respect to the direction of the cluster's orbit) are more stable against escape than prograde orbits, and predicted that a star cluster might acquire retrograde rotation through preferential escape of stars on prograde orbits. In this study we present evidence of this prediction, but we also illustrate that there are additional effects that cannot be accounted for by the preferential escape of prograde orbits alone. Specifically, in the early evolution, initially underfilling models increase their fraction of retrograde stars without losing significant mass, and acquire a retrograde angular velocity. We attribute this effect to the development of preferentially eccentric/radial orbits in the outer regions of star clusters as they are expanding into their tidal limitation. We explore the implications of the evolution of the fraction of prograde and retrograde stars for the evolution of the cluster internal rotation, and its dependence on the initial structural properties. Although all the systems studied here evolve towards an approximately solid-body internal rotation with angular velocity equal to about half of the angular velocity of the cluster orbital motion around the host galaxy, the evolutionary history of the radial profile of the cluster internal angular velocity depends on the cluster initial structure.

Tidal Expiratory Flow Limitation at Rest as a Functional Marker of Pulmonary Emphysema in Moderate-to-Severe COPD

Background: Tidal expiratory flow limitation (EFL) is a step of paramount importance in the functional decline in COPD. Among mechanisms contributing to EFL, loss of airway-parenchymal interdependence could mostly be involved. Aim: To assess if EFL is a functional marker more frequently linked to prevalent pulmonary emphysema rather than to prevalent chronic bronchiolitis in COPD patients with moderate-to-severe airflow obstruction. Methods: Forty consecutive stable COPD patients with FEV1 between 59 and 30% of predicted were functionally evaluated by measuring spirometry, maximal flow-volume curve and lung diffusion capacity (DLCO) and coefficient of diffusion (KCO). EFL was assessed by the negative expiratory pressure (NEP) method both in sitting and supine position. Chronic dyspnea was also scored by modified Medical Research Council (mMRC) scale. Results: In sitting position 13 patients (33%) were flow limited (FL) and 27 were non-flow limited (NFL). Only FEV1/FVC, FEV1 and MEF25–75% were different between FL and NFL patients (p < 0.01). In supine position, however, among NFL patients in sitting position those who developed EFL, had significantly lower values of DLCO and KCO (p < 0.05) and higher mMRC score (p < 0.01), but similar values of FEV1 as compared to those who did not have EFL. Conclusions: In COPD EFL in sitting position is highly dependent by the severity of airflow obstruction. In contrast, the occurrence of EFL in supine position is associated with worse DLCO and KCO and greater chronic dyspnea, reflecting a prevalent emphysematous phenotype in moderate-to-severe COPD patients.

Pulmonary Dysfunction in COPD

Pulmonary Dysfunction in COPD

DEEPCHANDRAMONITORING OBSERVATIONS OF NGC 4649. II. WIDE-FIELDHUBBLE SPACE TELESCOPEIMAGING OF THE GLOBULAR CLUSTERS

We present g and z photometry and size estimates for globular clusters (GCs) in the massive Virgo elliptical NGC 4649 (M60) using a five-pointing Hubble Space Telescope/Advanced Camera for Surveys mosaic. The metal-poor GCs show a monotonic negative metallicity gradient of (-0.43 +/- 0.10) dex per dex in radius over the full radial range of the data, out to ~ 24 kpc. There is evidence for substantial color substructure among the metal-rich GCs. The metal-poor GCs have typical sizes ~ 0.4 pc larger than the metal-rich GCs out to large galactocentric distances (~> 20 kpc), favoring an intrinsic explanation for the size difference rather than projection effects. There is no clear relation between half-light radius and galactocentric distance beyond ~ 15 kpc, suggesting that the sizes of GCs are not generically set by tidal limitation. Finally, we identify ~ 20 candidate ultra-compact dwarfs that extend down to surprisingly faint absolute magnitudes (M_z ~ -8.5), and may bridge the gap between this class and "extended clusters" in the Local Group. Three of the brighter candidates have published radial velocities and can be confirmed as bona fide ultra-compact dwarfs; follow-up spectroscopy will determine the nature of the remainder of the candidates.

The Volumetric Response to Bronchodilators in Stable Chronic Obstructive Pulmonary Disease

A significant proportion of patients with COPD show post-bronchodilator improvement in lung volume even though this response is rarely considered when classifying subjects as having reversible or irreversible airway disease. We studied 266 patients with a clinical and physiological diagnosis of COPD who underwent pulmonary function testing and had their spirometric response to 5 mg salbutamol assessed. After the bronchodilator 125 (47%) patients increased their forced vital capacity by more than the known variability of the test while 60 (23%) showed only a volume response without improvement in expiratory flow. These ‘volume responders’ had greater degrees of airflow obstruction–lower FEV1 (p < 0.001) and FEV1/FVC (p < 0.05)—and a higher residual volume at rest (p = 0.005) with similar degrees of emphysema measured by KCO. Subjects with evidence of greater dynamic airway collapse, assessed by the ratio of early to mid expiratory flow, were less likely to have a flow response but more likely to have a volume response after salbutamol (p < 0.005). This would be compatible with volume response being commoner in patients who exhibit tidal expiratory flow limitation. We suggest that post-bronchodilator absolute change in FVC provides important additional physiological information when interpreting bronchodilator reversibility testing.

Predictive Value of Infant Lung Function Testing for Airway Malacia

Airway malacia is present in a small proportion of wheezing infants. The usefulness of infant lung-function testing (ILFT) in ruling out malacia in wheezy infants is unknown. We assessed the predictive value of ILFT parameters for airway malacia diagnosed by flexible bronchoscopy. Thirty-two term infants (mean (SD) age, 11.0 (4.6) months) with chronic wheeze unresponsive to asthma treatment underwent ILFT prior to bronchoscopy. Functional residual capacity measured by plethysmograph (FRCp), maximal flow at FRC (V'max(FRC)), and tidal breathing parameters were obtained. Expiratory flow-volume curves were visually examined for tidal flow limitation. Malacia was observed during bronchoscopy in 20 infants. V'max(FRC) (Z-score) was significantly lower in the group with malacia as compared with the group without malacia. Lung-function measurements had a low negative predictive value and sensitivity. While flow limitation during tidal breathing was highly predictive and 100% specific for airway malacia, only half of the infants with malacia had tidal flow limitation. In this selected group of infants, routine lung function testing could not discriminate between infants with and without airway malacia. However, the presence of tidal flow limitation was 100% predictive and specific for airway malacia.

Haemodynamic and volumetric response to tidal volume and positive end expiratory pressure variation in acute lung injury/acute respiratory distress syndrome patients

Tidal volume limitation and incremental positive end expiratory pressure (PEEP) correlates with improved survival in acute respiratory distress syndrome (ARDS) [1], but the impact on haemodynamic response is not well established [2,3].

The effects of photoionization on galaxy formation — III. Environmental dependence in the luminosity function

Using semi-analytic modeling techniques, we calculate the luminosity function of galaxy populations residing in cold dark matter halos of different mass. We pay particular attention to the influence of the reionization of the Universe on the number of faint galaxies and to the effects of dynamical friction and tidal limitation of satellites on the number of bright galaxies. We find substantial differences in the shapes of the galaxy luminosity functions in halos of different mass which reflect generic features of the cold dark matter model of galaxy formation and thus offer the opportunity to test it. We then consider how the individual halo luminosity functions combine together to produce the global luminosity function. Surprisingly, the global function ends up having a shallower faint end slope than those of the constituent halo luminosity functions. We compare our model predictions with the limited datasets compiled by Trentham & Hodgkin. We find good agreement with the luminosity functions measured in the Virgo and Coma clusters but significant disagreement with the luminosity functions measured in the Local Group and Ursa Minor cluster. We speculate on possible inadequacies in our modeling and in the existing observational samples. The luminosity functions of galaxies in groups and clusters identified in the 2dF and SDSS galaxy redshift surveys offer the prospect of testing galaxy formation models in detail.

Mechanical ventilation in acute respiratory distress syndrome

The acute respiratory distress syndrome occurs commonly in critical care. There is an increasing volume of clinical and experimental evidence that poor ventilatory technique that is injurious to the lungs can propagate the systemic inflammatory response and adversely affect mortality. Many ventilatory techniques have been hypothesized to 'protect' the lungs during mechanical ventilation, including tidal volume limitation, high positive end-expiratory pressure, pressure-controlled inverse ratio ventilation, and prone positioning. Experimental techniques include liquid ventilation, surfactant administration and extracorporeal gas exchange. Despite excellent rationale for their use, few techniques, apart from tidal volume limitation, have been shown to improve survival in randomized controlled trials.

Monte Carlo simulations of star clusters -- II. Tidally limited, multimass systems with stellar evolution

A revision of Stodółkiewicz's Monte Carlo code is used to simulate evolution of large star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. A survey of the evolution of N-body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross-section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods (Fokker–Planck, Monte Carlo and N-body). The initial rapid mass loss, resulting from stellar evolution of the most massive stars, causes expansion of the whole cluster and eventually leads to the disruption of less bound systems (W0=3). Models with larger W0 survive this phase of evolution and then undergo core collapse and subsequent post-collapse expansion, like isolated models. The expansion phase is eventually reversed when tidal limitation becomes important. The results presented are the first major step in the direction of simulating evolution of real globular clusters by means of the Monte Carlo method.

Measuring Mass Loss Rates from Galactic Satellites

Number count profiles of many Galactic and some extra-galactic satellite systems show evidence for associated stars beyond the cut-off in density that is identified as the point of tidal limitation (e.g. Irwin &amp; Hatzidimitriou 1995, Grillmair et al. 1995). These “extra-tidal” stars are assumed to be debris lost from the satellite due to heating or stripping by the Galactic tidal field or (in the case of globular clusters) evaporation of stars over the tidal boundary. In this contribution we present a method for using these features to measure the mass loss rate from the satellite, and test it on the results of numerical simulations of satellite disruption. A more detailed discussion of all aspects of this work can be found in Johnston, Sigurdsson &amp; Hemquist (1998).In the numerical simulations, the satellite’s evolution along an orbit in a three component rigid model of the Galaxy is followed using a self-consistent field (SCF) code (developed by Hernquist &amp; Ostriker 1992) to calculate the mutual interactions of stars in the satellite. Figure 1 shows the annularly averaged number surface density from one example simulation “observed” from the viewpoint of the center of the Galaxy after several Gigayears. The closed (open) symbols show the profile recovered if only bound (all) stars are considered. Clearly there is a break in the open symbols at the radius rbreak where the analysis becomes dominated by unbound stars.

The effect of the Galactic spheroid on globular cluster evolution

We study the combined effects of relaxation, tidal heating and binary heating on globular cluster evolution, exploring the physical consequences of external effects and examining evolutionary trends in the Milky Way population. Our analysis demonstrates that heating on circular and low-eccentricity orbits can dominate cluster evolution. The results also predict rapid evolution on eccentric orbits either due to strong relaxation caused by the high densities needed for tidal limitation or due to efficient bulge shocking of low density clusters. The combination of effects leads to strong evolution of the population as a whole. For example, within the solar circle, tidally-limited 10^5 M_sun clusters lose at least 40% of their mass in 10 Gyr. At high eccentricity most of these clusters evaporate completely. Bulge shocking disrupts clusters within 40 kpc which have less than 80% of their mass within their pericentric inner Lagrange point. Our results are consistent with suggestions that the shape of the cluster luminosity function results from evaporation and disruption of low mass clusters; they further predict that the net velocity dispersion of the cluster system in the inner Galaxy has decreased with time. Preliminary constraints on formation models are also discussed. We conclude that the observed cluster system has largely been shaped by dynamical selection.

The relationship between wheezing and lung mechanics during methacholine-induced bronchoconstriction in asthmatic subjects.

Wheeze is a classic sign of airflow obstruction but relatively little is known of its mechanism of production or its relationship to the development of airflow obstruction. We studied eight asthmatic subjects age (mean +/- 5D) 42 +/- 5 yr, FEV1 2.46 +/- 0.36 L during an extended, symptom-limited methacholine challenge test. Breath sounds were detected by a microphone over the right upper anterior chest. Spectral analysis was by a fast Fourier transform algorithm. Mean FEV1 fell by 51 +/- 14% to 1.28 +/- 0.61 L during the challenge and airways resistance increased by 119 +/- 50%. There were no consistent changes in breathing pattern or tidal volume during the challenge. Wheeze occurred late in the challenge at the highest concentration of methacholine administered and only after expiratory tidal flow limitation had been reached. Five subjects developed wheeze on tidal breathing, the remaining three only wheezed on deep breathing. Wheezing sounds were reproducible between breaths, coefficient of variation of starting sound frequency was 4.2% and ending frequency 12%. Mean frequency of expiratory wheezes was 669 +/- 100 Hz and inspiratory wheezes 710 +/- 76 Hz. Expiratory wheeze fell in pitch during a breath (mean fall in sound frequency 187 +/- 43 Hz) but inspiratory wheezes were more variable. Expiratory wheezes occurred late in the respiratory cycle at a mean of 58% of the maximal tidal expiratory flow, whereas inspiratory wheezes occurred around maximal tidal inspiratory flows, suggesting that the mechanisms of production of inspiratory and expiratory wheezes may be different. In this model, the presence of wheeze during tidal breathing was a sign of severe airflow limitation.

Tidal limitation of stellar systems on both circular and elongated orbits

Extensive numerical simulations were performed to support a theoretical discussion of first-order tidal limitation of satellites on both circular and elongated orbits in softened external potentials. The existing theory is good for satellites on circular orbits but fails dramatically for noncircular orbits. The mass distribution is much less strongly truncated for elongated orbits than conventionally determined by circular theory applied at pericenter. A new first-order theory for elongated orbits is presented which is in good agreement with the simulations for pericenter not too close to the softened cluster center. For an analytic King model external potential with core radius a-prime, the theory is good down to a pericenter of 3(a-prime). Below this the maximum tide is no longer at pericenter and the theory is inappropriate. Successive passages through pericenter do not noticeably reduce the tidal radius, although continual small mass loss from second-order heating is apparent. The importance of mean field tidal limitation on galaxy evolution in clusters have been overestimated in recent studies. Galaxies on noncircular orbits in clusters are well within their tidal radii even if they pass within one core radius of the center of the cluster. 14 references.

Dynamic Evolution of Rich Galactic Star Clusters. I

view Abstract Citations (31) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dynamic Evolution of Rich Galactic Star Clusters. I Prata, Stephen W. Abstract Results are presented of a theoretical study of the dynamic evolution of rich galactic star clusters. The model uses a distribution of stellar masses and takes into account tidal limitation, star loss, gas loss, and tidal shocks. The evolution of the mass function depends primarily on the mass function itself (including scaling) and only secondarily on the cluster structure. M67's original mass function was strongly deficient in low-mass stars. M67's continued existence is the result of a fortunate combination of initial conditions. Effects of a mass mixture on star loss are discussed. General comments on cluster evolution are made. Publication: The Astronomical Journal Pub Date: December 1971 DOI: 10.1086/111216 Bibcode: 1971AJ.....76.1017P full text sources ADS | data products SIMBAD (1)