22 research outputs found
Microphysical time scales and local supersaturation balance at a warm Cloud Top Boundary, ERCOFTAC
Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodispersed and polydisperse droplets. For the monodisperse population,a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities
Microphysical time scales, supersaturation fluctuations and droplet distance-neighbour statistical analysis at a warm Cloud Top Boundary
Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplet populations. For the monodisperse population, a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities
The Principle of Strain Reconstruction Tomography: Determination of Quench Strain Distribution from Diffraction Measurements
Evaluation of residual elastic strain within the bulk of engineering
components or natural objects is a challenging task, since in general it
requires mapping a six-component tensor quantity in three dimensions. A further
challenge concerns the interpretation of finite resolution data in a way that
is commensurate and non-contradictory with respect to continuum deformation
models. A practical solution for this problem, if it is ever to be found, must
include efficient measurement interpretation and data reduction techniques. In
the present note we describe the principle of strain tomography by high energy
X-ray diffraction, i.e. of reconstruction of the higher dimensional
distribution of strain within an object from reduced dimension measurements;
and illustrate the application of this principle to a simple case of
reconstruction of an axisymmetric residual strain state induced in a
cylindrical sample by quenching. The underlying principle of the analysis
method presented in this paper can be readily generalised to more complex
situations.Comment: 10 pages, 6 figure
The Principle of Strain Reconstruction Tomography: Determination of Quench Strain Distribution from Diffraction Measurements
Evaluation of residual elastic strain within the bulk of engineering
components or natural objects is a challenging task, since in general it
requires mapping a six-component tensor quantity in three dimensions. A further
challenge concerns the interpretation of finite resolution data in a way that
is commensurate and non-contradictory with respect to continuum deformation
models. A practical solution for this problem, if it is ever to be found, must
include efficient measurement interpretation and data reduction techniques. In
the present note we describe the principle of strain tomography by high energy
X-ray diffraction, i.e. of reconstruction of the higher dimensional
distribution of strain within an object from reduced dimension measurements;
and illustrate the application of this principle to a simple case of
reconstruction of an axisymmetric residual strain state induced in a
cylindrical sample by quenching. The underlying principle of the analysis
method presented in this paper can be readily generalised to more complex
situations.Comment: 10 pages, 6 figure
The Principle of Strain Reconstruction Tomography: Determination of Quench Strain Distribution from Diffraction Measurements
Evaluation of residual elastic strain within the bulk of engineering
components or natural objects is a challenging task, since in general it
requires mapping a six-component tensor quantity in three dimensions. A further
challenge concerns the interpretation of finite resolution data in a way that
is commensurate and non-contradictory with respect to continuum deformation
models. A practical solution for this problem, if it is ever to be found, must
include efficient measurement interpretation and data reduction techniques. In
the present note we describe the principle of strain tomography by high energy
X-ray diffraction, i.e. of reconstruction of the higher dimensional
distribution of strain within an object from reduced dimension measurements;
and illustrate the application of this principle to a simple case of
reconstruction of an axisymmetric residual strain state induced in a
cylindrical sample by quenching. The underlying principle of the analysis
method presented in this paper can be readily generalised to more complex
situations.Comment: 10 pages, 6 figure
Intermittency acceleration of water droplet population dynamics inside the interfacial layer between cloudy and clear air environments
We use direct numerical simulation to study the temporal evolution of a
perturbation localized on the turbulent layer that typically separates a cloud
from the surrounding clear air. Across this shearless layer, a turbulent
kinetic energy gradient naturally forms. Here, a finite perturbation in the
form of a local initial temperature fluctuation is applied to simulate a
hydrodynamic instability inside the background turbulent air flow. A numerical
initial value problem for two diametrically opposite types of drop population
distributions is then solved. Specifically, we consider a mono-disperse
population of droplets of 15 m of radius and a poly-disperse distribution
with radii in the range 0.6 - 30 m. For both distributions, it is observed
that the evaporation and condensation have a dramatically different weight
inside the homogeneous cloudy region and the interfacial anisotropic mixing
region. It is observed that the dynamics of drop collisions is highly effected
by the turbulence structure of the host region. The two populations show a
common aspect during their energy decay transient. That is the increased
probability of collisions in the interfacial layer hat houses intense
anisotropic velocity fluctuations. This layer, in fact, induces an enhanced
differentiation on droplets kinetic energy and sizes. Both polydisperse and
monodisperse initial particle distributions contain droplets, matching
an initial liquid water content of . An estimate of the turbulent
collision kernel for geometric collisions used in the population balance
equations is given. A preliminary discussion is presented on the structure of
the two unsteady non ergodic collision kernels obtained inside the cloud
interface region.Comment: Turbulent shearless layer, Cloud-clear air interaction, Inertial
particles, Water droplets, DNS, Gravity effects, Collision kerne
Agreement Between Swept-source Optical Coherence Tomography and Rotating Scheimpflug Camera in Measurement of Corneal Parameters in Normal and Keratoconic Eyes
Purpose: This study aimed to assess the agreement between topographic indices of healthy subjects and keratoconus (KCN) patients using a swept-source optical coherence tomography (SS-OCT CASIA2) versus a Scheimpflug camera (Pentacam). Methods: 40 eyes of 23 patients with KCN and 40 eyes of 20 healthy subjects were included and evaluated with the CASIA2, followed by the Pentacam. Two consecutive modalities were obtained for one eye of each patient. Corneal parameters, including anterior keratometry at steep (Ks) and flat meridians (Kf), anterior astigmatism, anterior and posterior corneal elevation values, thinnest corneal thickness, and apex corneal thickness, were evaluated. Results: CASIA2 and Pentacam showed perfect agreement (95% limits of agreement (LoA): -0.22 to 0.68, 95% LoA: -1.5 to 1.44 D) and good correlation (Intraclass correlation (ICC):0.986, ICC:0.987; to 0.68, 95% LoA: -1.5 to 1.44 D) and good correlation (Intraclass correlation (ICC):0.986, ICC:0.987; P <0.01) for anterior (Ks) in normal and ectatic corneas, respectively. The cylinder amount had moderate agreement and correlation (95% LoA: -0.55 to 0.47D, ICC: 0.797, P <0.01) in normal, and moderate to strong agreement and correlation (95% LoA: -1.57 to 0.87D, ICC=0.911, P <0.01) in Keratoconic eyes. There was a fair agreement for anterior and posterior corneal elevation values in normal subjects (95% LoA: -3.09 to 4.59, 95% LoA: -6.91 to 7.31D). The thinnest corneal thickness amount had an excellent agreement in normal and KCN patients (ICC: 0.983, 0.953; respectively). Conclusions: Although the devices had different mean indices values, they had a good agreement based on the Bland–Altman plots. Since Pentacam is accepted as the standard tool for diagnosing ectatic cornea, pentacam CASIA2 is also helpful for early diagnosis of KCN
Free flying cluster of miniaturized radiosondes for multi-parameter atmospheric fluctuation observations
We present a newly developed methodology to track Lagrangian fluctuations of physical and chemical quantities in the atmosphere. The measurements are carried out by using a freely floating cluster of mini, innovative radiosondes. The radiosonde are light (∼20 gr) and are carried out by biodegradable small balloons. The primary aim of this method is to obtain Lagrangian statistics of the turbulence fluctuations inside warm clouds, their boundaries and the surrounding sub-saturated environmental air. This is important information, difficult to find at the state of the art and very useful for modeling cloud formations which are still a primary source of uncertainty in the numerical simulation of climatic and meteorological information
Microphysical time scales, supersaturation fluctuations and at a warm Cloud Top Boundary in temporal decay
Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient1 We have analyzed the supersaturation balance in this region, which
is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We
have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplet populations