scholarly journals Stem embolism vulnerability curve depends on methods used: is there a fifth mechanism of cavitation?

2022 ◽  
Author(s):  
Guoquan Peng ◽  
Lei Cao ◽  
Zhiyang Ren ◽  
Zhao Liang ◽  
Guo Yu ◽  
...  

A long-established ecological paradigm predicts a functional relationship determining vulnerability to cavitation: vulnerability increases with vessel hydraulic efficiency and vessel diameter. Even within a species, big vessels cavitate before small ones. Some centrifuge methods for measuring vulnerability are prone to artifacts due to nano-particles seeding early embolism, as the particles are drawn into vessels during measurements. Both the Sperry and Cochard rotors are prone to early cavitation due to nano-particles drawn into long and wide vessels in Robinia pseudoacacia and Quercus acutissima, whereas extraction centrifuge methods produce vulnerability curves more resistant to cavitation. Sufficient nano-particles pass through the stems to seed early embolism in all rotor designs. For several years, people have thought that early embolism is induced by nano-particles present in laboratory water. One new hypothesis is that the origin of nano-particles is from cut-open living cells but a much bigger study including many species is required to confirm this idea. This paper confirms the hypothesis in comparisons between short-vesselled Acer, and long-vesselled Robinia, and Quercus. Our new results and a review of old results justifies bigger study. Hypothetical nano-particles might explain why different methods for measuring vulnerability curves cause different T50 = tensions causing 50% loss of hydraulic conductivity. Hence the hypothesis for future research should be that the open-vessel artifact is consistent with 'long' vessels surrounded by cut open living cells.

2021 ◽  
Vol 12 ◽  
Author(s):  
Xiao Liu ◽  
Ning Wang ◽  
Rong Cui ◽  
Huijia Song ◽  
Feng Wang ◽  
...  

Precise and accurate estimation of key hydraulic points of plants is conducive to mastering the hydraulic status of plants under drought stress. This is crucial to grasping the hydraulic status before the dieback period to predict and prevent forest mortality. We tested three key points and compared the experimental results to the calculated results by applying two methods. Saplings (n = 180) of Robinia pseudoacacia L. were separated into nine treatments according to the duration of the drought and rewatering. We established the hydraulic vulnerability curve and measured the stem water potential and loss of conductivity to determine the key points. We then compared the differences between the calculated [differential method (DM) and traditional method (TM)] and experimental results to identify the validity of the calculation method. From the drought-rewatering experiment, the calculated results from the DM can be an accurate estimation of the experimental results, whereas the TM overestimated them. Our results defined the hydraulic status of each period of plants. By combining the experimental and calculated results, we divided the hydraulic vulnerability curve into four parts. This will generate more comprehensive and accurate methods for future research.


2021 ◽  
Vol 14 (7) ◽  
pp. 671
Author(s):  
Jéssica Lopes-Nunes ◽  
Paula Oliveira ◽  
Carla Cruz

G-quadruplexes (G4s) are a class of nucleic acids (DNA and RNA) with single-stranded G-rich sequences. Owing to the selectivity of some G4s, they are emerging as targeting agents to overtake side effects of several potential anticancer drugs, and delivery systems of small molecules to malignant cells, through their high affinity or complementarity to specific targets. Moreover, different systems are being used to improve their potential, such as gold nano-particles or liposomes. Thus, the present review provides relevant data about the different studies with G4s as drug delivery systems and the challenges that must be overcome in the future research.


2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
Mengji Shi ◽  
Kaiyu Qin

The paper provides a novel cooperative motion scheme for networked Unmanned Aerial Vehicles (UAVs) to fully sweep-cover a priori unknown elongated areas with curved borders, which are termed “valley areas.” The UAVs’ motion is confined between the borders. Different from former research on straight-corridor-sweep-coverage, in each valley area, the width of different portions varies dramatically: the UAVs need to line up across the valley area to achieve full coverage of the widest portions while they can only pass through the narrowest parts one by one in a queue. The UAVs are provided with barrier detection and inter-UAV communication. According to the scheme, a distributed control law has been offered for discrete-time multi-UAV systems, guaranteeing crash avoidance and full coverage while considering the constrained mobility of the UAVs. Regular and extreme simulations are carried out to verify the efficacy and stability of the proposed algorithm. Solutions to U-shaped valley coverage and the case of insufficient UAVs available are discussed with validation simulations. Comparison simulations are conducted with respect to a line-sweep-coverage algorithm developed by a closely related work, and differences in performance are revealed subsequently. Conclusions are drawn with possible directions of future research.


2020 ◽  
Vol 11 ◽  
Author(s):  
Xiao Liu ◽  
Qiang Li ◽  
Feng Wang ◽  
Xiaohan Sun ◽  
Ning Wang ◽  
...  

Plants may maintain long-term xylem function via efficiency-safety tradeoff and segmentation. Most studies focus on the growing season and community level. We studied species with different efficiency-safety tradeoff strategies, Quercus acutissima, Robinia pseudoacacia, Vitex negundo var. heterophylla, and Rhus typhina, to determine the seasonality of this mechanism. We separated their branches into perennial shoots and terminal twigs and monitored their midday water potential (Ψmd), relative water content (RWC), stem-specific hydraulic conductivity (Ks), loss of 12, 50, and 88% of maximum efficiency (i.e., P12, P50, P88) for 2 years. There were no correlations between water relations (Ψmd, RWC, Ks) and embolism resistance traits (P12, P50, P88) but they significantly differed between the perennial shoots and terminal twigs. All species had weak annual hydraulic efficiency-safety tradeoff but strong segmentation between the perennial shoots and the terminal twigs. R. pseudoacacia used a high-efficiency, low-safety strategy, whereas R. typhina used a high-safety, low-efficiency strategy. Q. acutissima and V. negundo var. heterophylla alternated these strategies. This mechanism provides a potential basis for habitat partitioning and niche divergence in the changing warm temperate zone environment.


2019 ◽  
Vol 11 (17) ◽  
pp. 4741 ◽  
Author(s):  
Sheila Clark ◽  
Courtney Coughenour ◽  
Kelly Bumgarner ◽  
Hanns de la Fuente-Mella ◽  
Chantel Reynolds ◽  
...  

Walking is the most affordable, accessible, and environmentally friendly method of transportation. However, the risk of pedestrian injury or death from motor vehicle crashes is significant, particularly in sprawling metropolitan areas. The purpose of this study was to examine the effect of pedestrian crossing flags (PCFs) on driver yielding behaviors. Participants crossed a marked, midblock crosswalk on a multilane road in Las Vegas, Nevada, with and without PCFs, to determine if there were differences in driver yielding behaviors (n = 160 crossings). Trained observers recorded (1) the number of vehicles that passed in the nearest lane without yielding while the pedestrian waited at the curb and (2) the number of vehicles that passed through the crosswalk while the pedestrian was in the same half of the roadway. ANOVA revealed that drivers were significantly less likely to pass through the crosswalk with the pedestrian in the roadway when they were carrying a PCF (M = 0.20; M = 0.06); drivers were more likely to yield to the pedestrian waiting to enter the roadway when they were carrying a PCF (M = 1.38; M = 0.95). Pedestrian crossing flags are a low-tech, low-cost intervention that may improve pedestrian safety at marked mid-block crosswalks. Future research should examine driver fade-out effects and more advanced pedestrian safety alternatives.


Author(s):  
Jon P. Nelson ◽  
John R. Moran

Abstract This paper conducts the first review and meta-analysis for estimates of alcohol excise tax pass-through rates. A total of 30 empirical studies are examined. Several widely cited studies indicate substantial overshifting, suggesting imperfectly-competitive markets for alcohol. The narrative review provides insights for data coverage by country; econometric models; and results for under- or overshifting by beverage. Weighted-averages calculated for two samples show that beer taxes are overshifted and wine-spirits taxes are fully shifted. Meta-regressions corrected for publication bias indicate, however, that full-shifting cannot be rejected for any beverage. Results are useful for alcohol tax policy and future research on optimal taxation and incidence.


PEDIATRICS ◽  
1955 ◽  
Vol 15 (3) ◽  
pp. 358-366
Author(s):  
Frederick C. Robbins ◽  
Eli Gold

INTRODUCTION IT WILL not be possible to cover exhaustively the field of virus and rickettsial diseases in this brief summary. The growth and basic properties of viruses and rickettsiae as well as the pathogenesis of diseases due to these agents will be reviewed in outline form. Epidemiology and immunity and current opinion on prophylaxis and therapy will be discussed. Finally, we will consider some recent developments and speculate a bit on what the future may offer. It is hoped that some of the more basic material presented, although admittedly elementary, will help to orient the reader. An understanding of some of the procedures conducted in the virus laboratory may make the physician aware not only of what can be done to help diagnostically, but also what cannot be done. FUNDAMENTAL INFORMATION CONCERNING PROPERTIES OF VIRUSES AND RICKETTSIAE A) Size 1) Rickettsiae are large enough to be seen with the light microscope and do not pass through porcelain filters. The rickettsia of Q fever does have filtrable form. 2) Viruses vary tremendously as to size. Some are highly complicated organisms (e.g., vaccinia), others such as tobacco mosaic virus, are apparently large protein molecules. Psittacosis and related organisms occupy intermediate position between rickettsiae and true viruses. B) Culture No virus or rickettsia has ever been propagated except in the presence of living cells. C) Life Cycle Most of time available information concerning infection of time cell and multiplication of viruses is derived from studies with bacterial viruses (bacteriophage). This may or may not be fully applicable to animal viruses but the cycle is represented below:


2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Tomasz Nawara ◽  
Tejeshwar Rao ◽  
Alexa Mattheyses

Clathrin-mediated endocytosis (CME) is an essential cellular process for internalizing nutrients and therapeutics at endothelial cell barriers. Studying the formation of cargo containing endocytic vesicles in living cells is challenging due to the limited resolution of fluorescence microscopy and the highly dynamic nature of CME. Moreover, it is currently unknown how the physiological conditions present in vasculature affect CME in endothelial cells. To address this challenge we used a novel microscopy approach, Simultaneous Two-wavelength Axial Ratiometry (STAR), to image vesicle formation dynamics with nanometer axial resolution in living cells. High-throughput analysis revealed that 80% of de novo clathrin accumulations contributed to endocytosis while 20% remained flat, consistent in both human umbilical vein endothelial cells (HUVECs) and our test-bed model green monkey kidney fibroblast-like (Cos-7) cells. We next investigated the interplay between coat curvature and clathrin accumulation in vesicle initiation to identify the mechanism of vesicle formation. Our results support the flexible model of vesicle formation with curvature and clathrin accumulation initiating together at shorter-lived vesicles (<20s) and through a flat-to-curved transition of clathrin lattices at longer-lived vesicles (>20s). Finally, we addressed if physiological conditions present in vasculature alter the dynamics of vesicle formation. We show that increasing osmotic pressure decreased the total number of internalizations but had no impact on the number of flat clathrin accumulations or the mechanism of vesicle formation in Cos-7 cells. In future research, we will test the hypothesis that HUVECs have distinct mechanisms to retain vesicle formation under osmotic pressure or shear stress conditions similar to their native environment. Additionally targeted drug delivery to vascular endothelial cells, for example nanocarriers binding to flat lattices or CCVs leading to different therapeutic outcomes or bioavailability, can potentially be informed by identifying clathrin morphology and dynamics and the mechanisms of endocytosis using STAR microscopy.


2019 ◽  
Vol 39 (1) ◽  
pp. 317-338 ◽  
Author(s):  
John Cawley ◽  
Anne Marie Thow ◽  
Katherine Wen ◽  
David Frisvold

During the past decade, dozens of countries, regions, and cities have enacted taxes on sugar-sweetened beverages (SSBs). They have been primarily motivated by a desire to raise prices, reduce sales and consumption, improve population health, and raise revenue. This review outlines the economic rationale for SSB taxes and illustrates their predicted effects. It reviews the research on the effects of these taxes on retail prices, sales, cross-border shopping, consumption, and product availability. The evidence indicates that the amount by which taxes increase retail prices (also called the pass-through of the tax) varies by jurisdiction, ranging from less than 50% to 100% of the tax. Sales tend to decrease significantly in the taxing jurisdiction, although this seems to be partly offset by residents increasingly shopping outside of the taxing jurisdiction (i.e., engaging in cross-border shopping).Overall, taxes lower consumption of the taxed beverages by adults, although not for all types of beverages or all groups of consumers. We conclude with suggestions for improving the design of such taxes and directions for future research.


2009 ◽  
Vol 97 (4-5) ◽  
Author(s):  
Renata Kierepko ◽  
Jerzy W. Mietelski ◽  
W. Borowiec ◽  
S. Tarasiewicz ◽  
S. Blazej ◽  
...  

AbstractThe appearance of plutonium isotopes in the environment was connected with the human activity, mainly: nuclear weapon tests (global fallout), nuclear accident in Chernobyl (1986), disintegration of satellite SNAP 9 (1963) and releases from nuclear reprocessing factories. At present, the concentration of plutonium in the atmosphere is very small but still observable.The aim of the study is to report and to discuss the results of plutonium alpha-emitters determination from sampling aerosols in air (Krakow 1990–1998, 2001–2002 and Bialystok 1996–1998, 2001) and in precipitation (Krakow 2005–2006). Plutonium activity concentration in air samples (in Krakow and Bialystok) varied in range: 0.22±0.04 nBq/mOne of the mechanisms responsible for the airborne plutonium is resuspension but on the other hand the main source of plutonium in the air seems to be marines aerosols from North See. This new hypothesis will be checked during the future research. The most interesting finding is the seasonal variation of plutonium air concentration. The conclusion from calculated ratio of plutonium isotopes (


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