Decrease In RI Research Articles

Fluid mechanical dispersion of airborne pollutants inside urban street canyons subjecting to multi-component ventilation and unstable thermal stratifications

The pedestrian level pollutant transport in street canyons with multiple aspect ratios (H/W) is numerically investigated in the present work, regarding of various unstable thermal stratification scenarios and plain surrounding. Non-isothermal turbulent wind flow, temperature field and pollutant spread within and above the street canyons are solved by the realizable k-ε turbulence model along with the enhanced wall treatment. One-vortex flow regime is observed for shallow canyons with H/W=0.5, whereas multi-vortex flow regime is observed for deep canyons with H/W=2.0. Both one-vortex and multi-vortex regimes could be observed for the street canyons with H/W=1.0, where the secondary vortex could be initiated by the flow separation and intensified by unstable thermal stratification. Air exchange rate (AER) and pollutant retention time are adopted to respectively evaluate the street canyon ventilation and pollutant removal performance. A second-order polynomial functional relationship is established between AER and Richardson number (Ri). Similar functional relationship could be established between retention time and Ri, and it is only valid for canyons with one-vortex flow regime. In addition, retention time could be prolonged abruptly for canyons with multi-vortex flow regime. Very weak secondary vortex is presented at the ground level of deep canyons with mild stratification, where pollutants are highly accumulated. However, with the decrease of Ri, pollutant concentration adjacent to the ground reduces accordingly. Present research could be applied to guide the urban design and city planning for enhancing pedestrian environment.

The Effects of Rituximab on Lipids, Arterial Stiffness and Carotid Intima-Media Thickness in Rheumatoid Arthritis.

The aim of the study was to examine lipid profiles, arterial stiffness (AS), carotid intima-media thickness (cIMT), in 55 women with RA without overt cardiovascular disease (СVD) treated with rituximab (RTX).The following parameters were recorded before and 24 weeks after RTX therapy (2 infusions of 500 or 1,000 mg RTX intravenously, fortnightly): plasma total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides, DAS 28-ESR, serum C-reactive protein (CRP), RF IgM, AS (SI - stiffness index, RI – reflection index) by digital volume pulse contour analysis (Micro Medical, UK), and common cIMT by high-resolution B-mode carotid ultrasound. Based on the European League Against Rheumatism (EULAR) criteria, patients were divided into two groups: 1) moderate/good response to RTX therapy after 24 weeks (41 patients, 75%), 2) no response to RTX therapy (14 patients, 25%). Effective RTX therapy resulted in 9% increase in TC, 23% increase in HDL-C and 14% decrease in atherogenic index, 57% decrease in SI and 24% decrease in RI. We observed a 9% decrease of cIMTmax at 24 weeks. The improvement of cardiovascular parameters was accompanied by statistically significant decreases of CRP, ESR, RF IgM and DAS 28 in group 1 (P < 0.05). There were not significant changes in lipid profile, AS parameters, and cIMT in group 2. Two infusions of RTX in case of moderate/good EULAR effect of therapy exerted favorable effects on lipid profile, AS and cIMT in women with RA without overt CVD.

Surgical management for the children testis torsion

It was performed the analysis of the treatment results of 140 patients with a testicular inversion. The aim of the publication was to improve the treatment results and to develop optimal surgical tactic with questionable viability of the testis. Analysis of relations has been carried out between degree of testicular atrophy and objective Doppler parameters (Ri, ISD) and their correlation with clinical reference points in a curative tactic - a duration of disease and a degree of inversion. It has been shown that the decrease of Ri below 0.5 and ISD below 1.5 clinically correlate with a disease for 24 hours and degree of inversion 270-360°. Thus the combination of a degree of inversion of 360° and disease for 24 hours actually leaves no chances to save the testicle, resulting either to urgent orchiectomy or to total atrophy, requiring removal of the gonads.

Dynamic 3D analysis of myocardial sympathetic innervation: an experimental study using 123I-MIBG and a CZT camera.

Data on the in vivo myocardial kinetics of (123)I-metaiodobenzylguanidine ((123)I-MIBG) are scarce and have always been obtained using planar acquisitions. To clarify the normal kinetics of (123)I-MIBG in vivo over time, we designed an experimental protocol using a 3-dimensional (3D) dynamic approach with a cadmium zinc telluride (CZT) camera. We studied 6 anesthetized pigs (mean body weight, 37 ± 4 kg). Left ventricular myocardial perfusion and sympathetic innervation were assessed using (99m)Tc-tetrofosmin (26 ± 6 MBq), (123)I-MIBG (54 ± 14 MBq), and a CZT camera. A normal perfusion/function match on gated SPECT was the inclusion criterion. A dynamic acquisition in list mode started simultaneously with the bolus injection of (123)I-MIBG, and data were collected every 5 min for the first 20 min and then at acquisition steps of 30, 60, 90, and 120 min. Each step was reconstructed using dedicate software and reframed (60 s/frame). On the reconstructed transaxial slice that best showed the left ventricular cavity, regions of interest were drawn to obtain myocardial and blood pool activities. Myocardial time-activity curves were generated by interpolating data between contiguous acquisition steps, corrected for radiotracer decay and injected dose, and fitted to a bicompartmental model. Time to myocardial maximum signal intensity (MSI), MSI value, radiotracer retention index (RI, myocardial activity/blood pool integral), and washout rate were calculated. The mediastinal signal was measured and fitted to a linear model. The myocardial MSI of (123)I-MIBG was reached within 5.57 ± 4.23 min (range, 2-12 min). The mean MSI was 0.426% ± 0.092%. Myocardial RI decreased over time and reached point zero at 176 ± 31 min (range, 140-229 min). The ratio between myocardial and mediastinal signal at 15 and 125 min and extrapolated at 176 and 4 h was 5.45% ± 0.61%, 4.33% ± 1.23% (not statistically significant vs. 15 min), 3.95% ± 1.46% (P < 0.03 vs. 125 min), and 3.63% ± 1.64% (P < 0.03 vs. 176 min), respectively. Mean global washout rate at 125 min was 15% ± 14% (range, 0%-34%), and extrapolated data at 176 min and 4 h were 18% ± 18% (range, 0.49%-45%) and 25% ± 23% (range, 1.7%-56.2%; not statistically significant vs. 176 min), respectively. 3D dynamic analysis of (123)I-MIBG suggests that myocardial peak uptake is reached more quickly than previously described. Myocardial RI decreases over time and, on average, is null about 3 h after injection. The combination of an early peak and variations in delayed myocardial uptake could result in a wide physiologic range of washout rates. Mediastinal activity appears to be constant over time and significantly lower than previously described in planar studies, resulting in a higher heart-to-mediastinum ratio.

The Role of Antioxidant Vitamin C on Imminent Abortion through Interaction of Superoxide Dismutase, Interferon-γ, Interleukin-4, Vascular Cells Adhesion Molecule-1, and Decidual Spiral Arteries Blood Flow

Imminent abortion needs more serious attention since it remains a big problem in Indonesia considering its epidemiology, morbidity, mortality, and prognosis. In fact, some cases can still be prevented. The objective of this study was to determine pathogenesis, diagnosis, and prognosis of imminent abortion through the role of antioxidant vitamin C in the interaction of superoxide dismutase (SOD), interferon-γ (IFN-γ), interleukin-4 (IL-4), vascular cells adhesion molecule-1 (VCAM-1), and decidual spiral artery resistance index (DSA RI). This study took 10 months from March to December 2007 at Obstetrics and Gynecology Department of Medical Faculty of Padjadjaran University/Hasan Sadikin Hospital, Bandung. Sixty pregnant women who met the inclusion and exclusion criteria were divided into two groups with the random clinical trial method, double-blind with repeated measurements. Data were analyzed statistically using t test, Mann-Whitney, Rank Spearman, Wilcoxon, t paired, and diagnostic test. The results of this study showed that the incidence of abortion in vitamin C group was 9 cases (30%) and placebo group was 13 cases (43.3%). There was a significant difference in SOD, IFN-γ, IL-4 and VCAM-1 level between groups of women with and without abortion (p ￡992 U/gHbwhich showed quite high sensitivity, specificity, accuracy, and significant difference (p γ, VCAM-1 and DSA RI (p γ level and the increase of IL-4 level in imminent abortion after vitamin C administration. There was a correlation between the increase of SOD level with the decrease of DSA RI and the decrease of VCAM-1 level in imminent abortion after vitamin C administration. In abortion, there was a decrease of SOD and IL-4 level, as well as an increase of IFN-γ, VCAM-1, and DSA RI level.

P14.15: Progesterone effect on fetal Doppler velocimetry in in pregnant women with IUGR and preterm labour

The purpose of this study was to determine whether supplementation of vaginal progesterone affects on fetal Doppler velocimetry. Thirty patients with intrauterine growth retardation fetuses and thirty pregnant women with threatened preterm labour fetuses were enrolled in the study. Fetal Doppler velocimetry was investigated before, 24 hours and two weeks after administration of vaginal progesterone. All fetuses demonstrated a significant decrease in PI and RI of fetal middle cerebral artery in both preterm and IUGR groups in three times. (P < 0.001). The reduction in PI, S/D and RI of umbilical artery after 24 hours was not significant, whereas after two weeks of treatment the reduction in PI was significant (P 0.004). The use of vaginal progesterone suppository led to a reduction middle cerebral artery PI and umbilical artery PI. It can improve fetoplacental perfusion in pregnancies complicated by IUGR and preterm labour.

Demand response modification factor for the investigation of inelastic response of base isolated structures

In this study, the effect of flexibility of superstructures and nonlinear characteristics of LRB (Lead Rubber Bearing) isolator on inelastic response of base isolated structures is investigated. To demonstrate the intensity of damage in superstructures, demand response modification factor without the consideration of damping reduction factor, demand RI, is used and the N2 method is applied to compute this factor. To evaluate the influence of superstructure flexibility on inelastic response of base isolated structures, different steel intermediate moment resisting frames with different heights have been investigated. In lead rubber bearing, the rubber provides flexibility and the lead is the source of damping; variations of aforementioned characteristics are also investigated on inelastic response of superstructures. It is observed that an increase in height of superstructure leads to higher value of demand RI till 4-story frame but afterward this factor remains constant; in other words, an increase in height until 4-story frame causes more damage in the superstructure but after that superstructure's damage is equal to the 4-story frame's. The results demonstrate that the low value of second stiffness (rubber stiffness in LRBs) tends to show a significant decrease in demand RI. Increase in value of characteristic strength (yield strength of the lead in LRBs) leads to decrease in the demand RI.

Demand response modification factor for the investigation ofinelastic response of base isolated structures

In this study, the effect of flexibility of superstructures and nonlinear characteristics of LRB (Lead Rubber Bearing) isolator on inelastic response of base isolated structures is investigated. To demonstrate the intensity of damage in superstructures, demand response modification factor without the consideration of damping reduction factor, demand RI, is used and the N2 method is applied to compute this factor. To evaluate the influence of superstructure flexibility on inelastic response of base isolated structures, different steel intermediate moment resisting frames with different heights have been investigated. In lead rubber bearing, the rubber provides flexibility and the lead is the source of damping; variations of aforementioned characteristics are also investigated on inelastic response of superstructures. It is observed that an increase in height of superstructure leads to higher value of demand RI till 4-story frame but afterward this factor remains constant; in other words, an increase in height until 4-story frame causes more damage in the superstructure but after that superstructure\'s damage is equal to the 4-story frame\'s. The results demonstrate that the low value of second stiffness (rubber stiffness in LRBs) tends to show a significant decrease in demand RI. Increase in value of characteristic strength (yield strength of the lead in LRBs) leads to decrease in the demand RI.

Bacterial infection of macrophages induces decrease in refractive index

Infection of cells by pathogens leads to both biochemical and structural modifications of the host cell. To study the structural modifications in a label-free manner, we use digital holographic microscopy, DHM, to obtain the integral refractive index distribution of cells. Primary murine bone marrow derived macrophages (BMDM) infected with Salmonella enterica serovar Typhimurium, undergo highly significant reduction in refractive index, RI, compared to uninfected cells. Infected BMDM cells from genetically modified mice lacking an inflammatory protein that causes cell death, caspase 1, also exhibit similar decrease in RI. These data suggest that any reduction in RI of Salmonella-infected BMDMs is pathogen induced and independent of caspase 1-induced inflammation or cell death. This finding suggests DHM may be useful for general real time monitoring of host cell interactions with infectious pathogens.

Light-Induced Plasticity of Synaptic AMPA Receptor Composition in Retinal Ganglion Cells

Light-evoked responses of all three major classes of retinal ganglion cells (RGCs) are mediated by NMDA receptors (NMDARs) and AMPA receptors (AMPARs). Although synaptic activity at RGC synapses is highly dynamic, synaptic plasticity has not been observed in adult RGCs. Here, using patch-clamp recordings in dark-adapted mouse retina, we report a retina-specific form of AMPAR plasticity. Both chemical and light activation of NMDARs caused the selective endocytosis of GluA2-containing, Ca(2+)-impermeable AMPARs on RGCs and replacement with GluA2-lacking, Ca(2+)-permeable AMPARs. The plasticity was expressed in ON but not OFF RGCs and was restricted solely to the ON responses in ON-OFF RGCs. Finally, the plasticity resulted in a shift in the light responsiveness of ON RGCs. Thus, physiologically relevant light stimuli can induce a change in synaptic receptor composition of ON RGCs, providing a mechanism by which the sensitivity of RGC responses may be modified under scotopic conditions.

Vaginal versus intramuscular progesterone in the prevention of preterm labor and their effect on uterine and fetal blood flow

To compare vaginal with intramuscular progesterone administration to prevent preterm labor and to detect the effect of both on the uterine and fetal circulations. Prospective comparative clinical trial. Eighty three pregnant women at 20–24 weeks gestation at risk of preterm labor were classified into: Thirty six women who received micronized progesterone tablets 200 mg vaginally daily (Group 1), 28 women who received 17 alpha hydroxyl progesterone caproate 250 mg intramuscular once weekly (Group 2), and 19 women who had not received any progesterone and settled as control group. Doppler examination of fetal middle cerebral artery, umbilical artery and uterine artery was done before and one week after progesterone administration, progesterone was continued till 36 weeks pregnancy or delivery. Incidence of preterm delivery, mean gestational age and birth weight at delivery, the need for neonatal intensive care unit admission and neonatal mortality. Doppler indices before and after progesterone administration was also measured and compared in both groups. The incidence of preterm delivery in Group 1 and Group 2 was significantly lower than in the control group (25%, 21.4% and 52%, respectively). A significant decrease in fetal MCA-PI and RI was noted after progesterone administration both vaginally and I.M. But a significant decrease in the mean uterine artery RI and PI was noted only after progesterone was administrated vaginally. Vaginally administrated progesterone was nearly as equally effective as intra muscular progesterone in the prevention of PTL in women at risk and both were associated with significant reduction in fetal MCA-PI and RI, but a significant reduction in uterine artery RI and PI was observed only after vaginal progesterone.

Estimating turbulent kinetic energy dissipation using the inertial subrange method in environmental flows

The inertial subrange dissipation method, where spectral fitting is performed on the velocity spectra inertial subrange, is commonly used to estimate the dissipation of turbulent kinetic energy ε in environmental flows. Anisotropy induced from mean shear or stratification can inhibit the use of certain velocity components or even make the inertial subrange unusable for estimating ε but often this issue is ignored, potentially leading to large errors in estimated ε. We developed and tested a methodology to determine reliably ε with the inertial subrange, taking into consideration the sampling program, the instrument, and the flow characteristics. We evaluated various misfit criteria for identifying the inertial subrange and described the statistical methods appropriate for spectral fitting. For shear flows, we defined a parameter B = Ls/η, where Ls is the shear length scale and η is the Kolmogorov length scale that describes the extent of anisotropy in the inertial subrange; this ratio of length scales is analogous to the ratio for stratified flows I = Lo/η, where Lo is the Ozmidov length scale. We assessed our methodology by applying it to two data sets with very different shear and stratification. When B was low, the high shear led to anisotropy and precluded the estimation of ε. To enable successful application of the inertial subrange dissipation method, we recommend measuring the mean stratification and the mean velocity profile to estimate shear. The Richardson number relates the two length scales Ri = (Ls/Lo)4/3 and shear dominates the largest turbulent length scales as Ri decreases, i.e., Ls &lt; Lo.

Effects of TIPS on global end-diastolic volume and cardiac output and renal resistive index in ICU patients with advanced alcoholic cirrhosis

The transjugular porto-systemic stent-shunt (TIPS) reduces portal pressure in cirrhotic patients and is used as a nonsurgical treatment for refractory ascites, recurrent variceal hemorrhage or hepatorenal syndrome. There are concerns regarding a negative impact on cirrhotic cardiomyopathy and deterioration of hyperkinetic circulatory dysfunction. We analyzed a prospectively maintained database containing hemodynamic data on cirrhotic ICU patients. Hemodynamic monitoring was performed using transpulmonary thermodilution (PiCCO, Pulsion Medical Systems, Munich, Germany). Renal perfusion was assessed by Doppler ultrasound during studies of portal and TIPS perfusion before and after the procedure. Complete data sets of 8 patients (4 male, 4 female, age 60 years (52-67), Child-Pugh-Turcotte score 10 (8-12)) were available. After TIPS, there was a substantial increase of GEDVI (646 ml/m2 (580-737) to 663 mL/m2 (643-792); p=0.036) that was even more pronounced at 24 hours (716 mL/m2 (663-821); P=0.012). CI increased from 3.3 L/min/m2 (3.1-4.2) to 3.9 L/min/m2 (3.6-5.3) (p=0.012) and 3.9 L/min/m2 (3.7-5.2) (p=0.017), respectively. There was a significant decrease of renal RI from 0.810 (0.781-0.864) to 0.746 (0.710-0.798) (p=0.028) and a transient increase of fractional excretion of sodium. SVRI (1737 dyn*s/cm5/m2 (1088 - 2115) vs. 1917 dyn*s/cm5/m2 (1368-2177) was not significantly altered immediately after TIPS but decreased to 1495 dyn*s/cm5/m2 (833-1765) at 24 hours (p=0.036)). There were no significant changes of mean arterial pressure (MAP). In conclusion, TIPS resulted in a pronounced increase of central blood volume. The observed hemodynamic effects are compatible with a preload driven increase of cardiac output and secondary decreases in SVRI and RI.

Índices de resistência nas artérias ovariana e uterina na fase lútea média em portadoras de esquistossomose mansônica na sua forma hepatoesplênica

to evaluate the repercussion of portal hypertension in the indexes of the ovarian, uterine and luteus body periphery arterial resistance, at the medium luteal phase of the menstrual cycle. in an observational study with transversal cohort, 28 patients with hepatosplenic schistosomiasis mansoni, submitted to splenectomy and ligation of the left gastric vein (HESO), a similar group of 28 patients who had not had the surgery (HESNO) and 29 healthy volunteers (HV) were submitted to Doppler fluxmetry in the medium luteal phase of the menstrual cycle. Pourcelot's resistance index has been used as RI=[(S-D)/S], in which S means the highest systolic speed, and D, the end of diastole. The best record in the ascendant branch of the uterine artery, in the ovarian artery, when accessible, or in the intraovarian artery, was chosen. When the luteus body was present, the RI was measured in its periphery. The data obtained were analyzed by Kruskal-Wallis and Mann-Whitney tests. there was no significant difference among the groups, concerning the mean RI of the ovarian arteries (Kruskal-Wallis, p=0.50). There was a tendency for higher right uterine artery RI in the HESNO group (Kruskal-Wallis, p<0.07), but it was similar in the left uterine artery (Kruskal-Wallis, p=0.14). Arterial RIs significantly lower have been observed in the luteus body periphery, when compared to the contralateral ovarian arteries in all the groups (Mann-Whitney, p<0.0001). there was no difference among the groups, regarding the ovarian and uterine RIs. The portal hypertension in patients with hepatosplenic schistosomiasis does not affect the natural phenomenon of arterial RI decrease in the ovary where ovulation occurs.

Bone Morphogenetic Protein-2 Antagonizes Renal Interstitial Fibrosis by Promoting Catabolism of Type I Transforming Growth Factor-β Receptors

TGF-beta is a therapeutic target for renal fibrosis. Scientists have long sought ways to antagonize TGF-beta to ameliorate diabetic nephropathy. Bone morphogenetic protein (BMP-2) is a member of the TGF-beta superfamily and is highly regulated in the kidney. Thus, the role of BMP-2 was investigated in NRK-49F cells (rat fibroblasts). We showed that TGF-beta1 induces an increase in fibronectin. Treatment with exogenous BMP-2 or pCMV-BMP-2 significantly reversed the TGF-beta1-induced increase in fibronectin concomitant with a significant decrease in type I TGF-beta receptors (TGF-beta RI). Moreover, BMP-2 significantly shortened the half-life of TGF-beta RI. These results are related to proteosomal activation because MG132, a proteasome inhibitor, abolished BMP-2-mediated degradation of TGF-beta RI. This was confirmed because BMP-2 time course dependently enhanced the ubiquitination level of TGF-beta RI. In addition, Smads would seem to be involved in the interaction of BMP-2 and TGF-beta. We demonstrated that BMP-2 significantly reversed the TGF-beta1-induced increase in pSmad2/3 and reversed the TGF-beta1-induced decrease in inhibitory Smad7. Most importantly, Smad7 small interfering RNA abolished the BMP-2-induced decrease in TGF-beta RI. We evaluated the clinical efficacy of BMP-2 using unilateral ureteral obstruction rats. BMP-2 was administered ip for 7 d. In the unilateral ureteral obstruction kidneys, interstitial fibrosis was prominent. However, treatment with BMP-2 dramatically reduced Masson's trichrome staining (collagen) in the interstitial and tubular areas of the kidneys concomitantly with a reduction in TGF-beta RI. These results suggest that BMP-2 acts as a novel fibrosis antagonizing cytokine partly by down-regulating TGF-beta RI and Smads.

674 The changes of peripheral blood flow and flow-mediated dilation in hypertensive patients with chronic heart failure under treatment with carvedilol

11.3±2.46 cm/s, p<0.01, respectively) and RI was significantly higher than in controls (0.84±0.01 vs 0.77±0.03 units, p<0.01). D was significantly more in control (11.04±1.3% compared to 6.44±0.52%, p<0.01). Under C treatment Vps and Ved substantially increased (from 34.5±1.61 to 42.3±1.88 cm/s, p<0.01 and from 5.5±0.34 to 11.0±2.4 cm/s, p<0.01, respectively) with cor- responding decrease of RI (from 0.84±0.01 to 0.80±0.01 units, p<0.01); D increased significantly from 6.44±0.52% to 8.81±0.41% (p<0.01) and 6mWT distance also significantly increased from 396.5±28.5 to 460.0±26.8 m (p<0.05). The increment of RI diminution under C treatment and D incre- ment after C treatment slightly correlated with 6 mWT distance increment after C (r=-0.385, p=0.052 and r=0.038, p=0.057, respectively). Conclusions: In stable CHF long-term treatment by C improves the exer- cise capacity evaluated by 6 mWT. This effect may be partly related to peripherial vascular effects of C (increase of arterial BF, improvement of flow- mediated dilation response). (WT), relative wall thickness (RWT), Ea, and E/Ea ratio were estimated. Results: Global diastolic dysfunction was evident in 64% of hypertensive (56% abnormal relaxation and 8% pseudonormal type) and 16.7% of control sub- jects. Filling pressures (E/Ea ratio) correlated with SystolicBP (r: 0.66, p<0.001), MAP (r: 0.47, p<0.05), WT (r: 0.39, p<0.05), RWT (r: 0.44, p<0.05), mean S (r: -0.31, p<0.05), mean SR (r: -0.48, p<0.001). Hypertensives had higher filling pressures (E/Ea: 11.3±3.8 vs 7.2±1.4, p<0.001) and lower mean S and SR (S: 18.1±2.2 vs 20.5±2.0%, p<0.05 and SR: 1.34±0.16 vs 1.54±0.13/s, p<0.05), compared to controls. Subjects with diastolic dysfunction had higher filling pressures (E/Ea: 11.7±4.2 vs 8.2±2.1, p<0.05) and lower mean longi- tudinal S and SR (S: 19.7±2.2 vs 18.0±2.3%, p<0.05 and SR: 1.32±0.18 vs 1.47±0.14/s, p<0.05) compared to those without diastolic dysfunction. Conclusion: Diastolic dysfunction and LV remodelling consist the principal pathophysiological factors, responsible for the elevated filling pressures in hypertension. Filling pressures are adversely related with longitudinal sys- tolic function in hypertensive disease.

A linear model of gravity wave drag for hydrostatic sheared flow over elliptical mountains

AbstractAn analytical model of orographic gravity wave drag due to sheared flow past elliptical mountains is developed. The model extends the domain of applicability of the well‐known Phillips model to wind profiles that vary relatively slowly in the vertical, so that they may be treated using a WKB approximation. The model illustrates how linear processes associated with wind profile shear and curvature affect the drag force exerted by the airflow on mountains, and how it is crucial to extend the WKB approximation to second order in the small perturbation parameter for these effects to be taken into account. For the simplest wind profiles, the normalized drag depends only on the Richardson number, Ri, of the flow at the surface and on the aspect ratio, γ, of the mountain. For a linear wind profile, the drag decreases as Ri decreases, and this variation is faster when the wind is across the mountain than when it is along the mountain. For a wind that rotates with height maintaining its magnitude, the drag generally increases as Ri decreases, by an amount depending on γ and on the incidence angle. The results from WKB theory are compared with exact linear results and also with results from a non‐hydrostatic nonlinear numerical model, showing in general encouraging agreement, down to values of Ri of order one. Copyright © 2006 Royal Meteorological Society

Initial Radical Separation after Photolysis of 2,2′‐Azobis(isobutyronitrile) (AIBN) in Solution: Modeling the Primary Cage Effect for Polar Radicals

AbstractThere is a contradiction as to the initial spatial separation ri of the two transient 2‐cyanoprop‐2‐yl radicals (Me2$\rm{{{\dot C}}}$CN) formed by flash photolysis of 2,2′‐azobis(isobutyronitrile) (AIBN) in solvents of various viscosities. The cage effect, expressed in terms of the in‐cage termination probability of the resulting radicals, is predicted correctly by classical Langevin models assuming a decrease of ri with increasing viscosity. However, the electron‐spin polarization of the radicals escaping the primary cage clearly indicates that the initial separation distance ri is independent of the solution viscosity. This obvious discrepancy can be reconciled by accounting for the strong electric dipole moments of these radicals and the resulting inter‐radical dipoledipole interaction potential.We propose a primary‐caging model for polar radicals in solution based on an attractive inter‐radical mean‐force potential. The model is applied to the flash photolysis of AIBN and shown to describe properly the viscosity dependence of both the in‐cage termination probability (cage effect) and the electron‐spin polarization of the escaping 2‐cyanoprop‐2‐yl radicals.

Resonant gravity‐wave drag enhancement in linear stratified flow over mountains

AbstractHigh‐drag states produced in stratified flow over a 2D ridge and an axisymmetric mountain are investigated using a linear, hydrostatic, analytical model. A wind profile is assumed where the background velocity is constant up to a height z1 and then decreases linearly, and the internal gravity‐wave solutions are calculated exactly. In flow over a 2D ridge, the normalized surface drag is given by a closed‐form analytical expression, while in flow over an axisymmetric mountain it is given by an expression involving a simple 1D integral. The drag is found to depend on two dimensionless parameters: a dimensionless height formed with z1, and the Richardson number, Ri, in the shear layer. The drag oscillates as z1 increases, with a period of half the hydrostatic vertical wavelength of the gravity waves. The amplitude of this modulation increases as Ri decreases. This behaviour is due to wave reflection at z1. Drag maxima correspond to constructive interference of the upward‐ and downward‐propagating waves in the region z&lt;z1, while drag minima correspond to destructive interference. The reflection coefficient at the interface z=z1 increases as Ri decreases. The critical level, zc, plays no role in the drag amplification. A preliminary numerical treatment of nonlinear effects is presented, where zc appears to become more relevant, and flow over a 2D ridge qualitatively changes its character. But these effects, and their connection with linear theory, still need to be better understood. Copyright © 2005 Royal Meteorological Society.

Relationship between light availability and species richness during fen grassland succession

The complex relation between standing crop and species richness in herbaceous plant communities is still one of the most intensively discussed topics in vegetation ecology. In this study, we focus on the extent to which light availability is able to explain this relationship in fen grasslands. We analyse changes of light availability (measured as relative irradiance, RI), standing crop and species richness during fen grassland succession. Our study include communities representing differences in drainage intensity and nutrient status (‘land use intensification sere’) and successional stages developing after abandonment (‘abandonment seres’). Both in the land use intensification sere and in the abandonment seres, we recorded an increase in standing crop reaching highest values of approx. 800 g m‐2. RI, species richness and number of small‐growing species declined in the successional seres. RI was highest in stands of low‐productive communities, where light compensation points (5% RI) were already attained at soil surface and light saturation points (30% RI) at soil surface or at 15 cm height. Horizontal heterogeneity of RI at soil surface and at 30 cm height decreased in the abandonment seres, but not at 30 cm height in the land use intensification sere. Furthermore, we detected a signiñcant negative relation between standing crop and RI. Species richness declined with increasing standing crop and thus consequently also with decreasing RI. This result points out that light competition might be of importance for this pattern. The number of small‐growing species decreased exponentially with an increase in standing crop (and decrease in RI). It can be assumed that low light availability negatively affects small‐growing species at standing crop values higher than 400–500 g m2. As the maintenance of small‐growing species and the improvement of habitat conditions for their establishment are important aims of nature conservation in fen grasslands, management strategies should be orientated at maintaining standing crops that are not higher than these values.