790 research outputs found
Transcutaneous measurement of volume blood flow
Blood flow velocity measurements, using Doppler velocimeter, are described. The ability to measure blood velocity using ultrasound is derived from the Doppler effect; the change in frequency which occurs when sound is reflected or transmitted from a moving target. When ultrasound of the appropriate frequency is transmitted through a moving blood stream, the blood cells act as point scatterers of ultrasonic energy. If this scattered ultrasonic energy is detected, it is found to be shifted in frequency according to the velocity of the blood cells, nu, the frequency of the incident sound, f sub o, the speed of sound in the medium, c, and the angle between the sound beam and the velocity vector, o. The relation describing this effect is known as the Doppler equation. Delta f = 2 f sub o x nu x cos alpha/c. The theoretical and experimental methods are evaluated
Affine T-varieties of complexity one and locally nilpotent derivations
Let X=spec A be a normal affine variety over an algebraically closed field k
of characteristic 0 endowed with an effective action of a torus T of dimension
n. Let also D be a homogeneous locally nilpotent derivation on the normal
affine Z^n-graded domain A, so that D generates a k_+-action on X that is
normalized by the T-action. We provide a complete classification of pairs (X,D)
in two cases: for toric varieties (n=\dim X) and in the case where n=\dim X-1.
This generalizes previously known results for surfaces due to Flenner and
Zaidenberg. As an application we compute the homogeneous Makar-Limanov
invariant of such varieties. In particular we exhibit a family of non-rational
varieties with trivial Makar-Limanov invariant.Comment: 31 pages. Minor changes in the structure. Fixed some typo
Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems
The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1-20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two-dimensional and basin-scale three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. Furthermore, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial
The Verticillium wilt problem in Australian cotton
© 2021, Australasian Plant Pathology Society Inc. Verticillium dahliae is a soil-borne phytopathogen and the causal agent of Verticillium wilt. It affects many agriculturally important crops around the world, including cotton. In Australia, the billion-dollar cotton industry is increasingly impacted by Verticillium wilt. Internationally it has been reported that the defoliating V. dahliae Vegetative Compatibility Group (VCG) 1A causes severe damage to cotton. In Australia however, the non-defoliating VCG2A is causing more severe damage to crops in fields than the defoliating VCG1A. This review examines the current research to understand the Australian V. dahliae situation, including current classification systems, genetic analyses and management strategies. It appears that virulence cannot be defined solely by VCG in Australian Verticillium dahliae isolates causing disease in cotton, and that the industry must continually adapt their practices in order to keep the disease under control
Pathological Narcissism in Adolescents: Relationships with Childhood Maltreatment and Internalizing and Externalizing Difficulties
Background: There are significant gaps in our understanding of vulnerable and grandiose narcissism in adolescents and whether it is associated with psychosocial difficulties as well as risk factors such as child maltreatment. Objective: The aim of this study was to examine vulnerable and grandiose narcissism in adolescents and young adults. Method: 570 participants (ages 14-21) from the community completed an online survey. Vulnerable and grandiose narcissism were assessed with the Pathological Narcissism Inventory, while psycho-social difficulties were assessed with the Child Behaviour Checklist and maltreatment with the Childhood Experiences of Care and Abuse Questionnaire. Results: Gender-specific age trends were identified, with narcissism appearing to decrease with age for females, while increasing for males into early adulthood. For females, vulnerable and grandiose narcissism was associated with maltreatment and partially mediated the relationship between abuse and neglect and internalizing and externalizing difficulties. Conclusion: These findings underscore the importance of considering the relationship between childhood maltreatment experiences and suggest that the relationship between such experiences and adolescent psychosocial difficulties may be partially accounted for by the negative impact that maltreatment has on narcissism
Atomic and Molecular Gas Components in Spiral Galaxies of the Virgo Cluster
Based on two models, we investigate the molecular-to-atomic gas ratio in
Virgo cluster galaxies in comparison with field galaxies. We show that the
enhanced metallicity for cluster members and the ram pressure stripping of
atomic gas from the disk periphery cannot fully explain the observed gas
component ratios. The additional environmental factors affecting the
interstellar medium and leading to an increase in the molecular gas fraction
should be taken into account for cluster galaxies.Comment: 11 pages, 4 figure
The rapid formation a large rotating disk galaxy three billion years after the Big Bang
[Abridged] Over the past two decades observations and theoretical simulations
have established a global frame-work of galaxy formation and evolution in the
young Universe. Galaxies formed as baryonic gas cooled at the centres of
collapsing dark matter halos. Mergers of halos led to the build up of galaxy
mass. A major step forward in understanding these issues requires well resolved
physical information on individual galaxies at high redshift. Here we report
adaptive optics, spectroscopic observations of a representative luminous star
forming galaxy when the Universe was only twenty percent of its age. The
superior angular resolution of these data reveals the physical and dynamical
properties of a high redshift galaxy in unprecedented detail. A large and
massive rotating proto-disk is channelling gas towards a growing central
stellar bulge hosting an accreting massive black hole.Comment: Narure, accepted (Released Aug 17th
An improved method for statistical studies of the internal kinematics of HII regions: the case of M 83
We present the integrated Halpha emission line profile for 157 HII regions in
the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot
interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the
importance of a good characterization of the instrumental response function for
the study of line profile shapes. The luminosity-velocity dispersion relation
is also studied, and in the log(L)-log(sigma) plane we do not find a linear
relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For
the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity
L=10^38.5 ergs, in full agreement with previous studies of other galaxies,
reinforcing the idea of using HII regions as standard candles.Comment: 13 pages, 9 figures, accepted for publication in MNRA
H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II
This is the second part of an H-alpha kinematics follow-up survey of the
Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program
is to shed new light on the role of baryons and their kinematics and on the
dark/luminous matter relation in the star forming regions of galaxies, in
relation with studies at other wavelengths. The data for 37 galaxies are
presented. The observations were made using Fabry-Perot interferometry with the
photon-counting camera FaNTOmM on 4 different telescopes, namely the
Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m,
and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are
computed using custom IDL routines designed for an optimal use of the data. The
kinematical parameters and rotation curves are derived using the GIPSY
software. It is shown that non-circular motions associated with galactic bars
affect the kinematical parameters fitting and the velocity gradient of the
rotation curves. This leads to incorrect determinations of the baryonic and
dark matter distributions in the mass models derived from those rotation
curves.Comment: 18 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. All
high-res. figures are available at
http://www.astro.umontreal.ca/fantomm/singsII
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