scholarly journals An Empirical Parameterization of Heterogeneous Ice Nucleation for Multiple Chemical Species of Aerosol

2008 ◽  
Vol 65 (9) ◽  
pp. 2757-2783 ◽  
Author(s):  
Vaughan T. J. Phillips ◽  
Paul J. DeMott ◽  
Constantin Andronache
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation ◽  
Large Scale ◽  
Water Saturation ◽  
Chemical Species ◽  
Spectral Width ◽  
Diffusion Chamber ◽  
Field Studies ◽  
Cloud Models ◽  
Multiple Species

Abstract A novel, flexible framework is proposed for parameterizing the heterogeneous nucleation of ice within clouds. It has empirically derived dependencies on the chemistry and surface area of multiple species of ice nucleus (IN) aerosols. Effects from variability in mean size, spectral width, and mass loading of aerosols are represented via their influences on surface area. The parameterization is intended for application in large-scale atmospheric and cloud models that can predict 1) the supersaturation of water vapor, which requires a representation of vertical velocity on the cloud scale, and 2) concentrations of a variety of insoluble aerosol species. Observational data constraining the parameterization are principally from coincident field studies of IN activity and insoluble aerosol in the troposphere. The continuous flow diffusion chamber (CFDC) was deployed. Aerosol species are grouped by the parameterization into three basic types: dust and metallic compounds, inorganic black carbon, and insoluble organic aerosols. Further field observations inform the partitioning of measured IN concentrations among these basic groups of aerosol. The scarcity of heterogeneous nucleation, observed at humidities well below water saturation for warm subzero temperatures, is represented. Conventional and inside-out contact nucleation by IN is treated with a constant shift of their freezing temperatures. The empirical parameterization is described and compared with available field and laboratory observations and other schemes. Alternative schemes differ by up to five orders of magnitude in their freezing fractions (−30°C). New knowledge from future observational advances may be easily assimilated into the scheme’s framework. The essence of this versatile framework is the use of data concerning atmospheric IN sampled directly from the troposphere.

Effects of Trust and Threat Messaging on Academic Cheating: A Field Study

2021 ◽  
pp. 095679762097751
Author(s):  
Li Zhao ◽  
Jiaxin Zheng ◽  
Haiying Mao ◽  
Xinyi Yu ◽  
Jiacheng Ye ◽  
...  
Keyword(s):  
Field Study ◽  
Academic Integrity ◽  
Large Scale ◽  
Theoretical Foundation ◽  
Empirical Evaluation ◽  
Psychological Theory ◽  
Field Studies ◽  
Educational Institutions ◽  
Academic Cheating ◽  
College Classrooms

Morality-based interventions designed to promote academic integrity are being used by educational institutions around the world. Although many such approaches have a strong theoretical foundation and are supported by laboratory-based evidence, they often have not been subjected to rigorous empirical evaluation in real-world contexts. In a naturalistic field study ( N = 296), we evaluated a recent research-inspired classroom innovation in which students are told, just prior to taking an unproctored exam, that they are trusted to act with integrity. Four university classes were assigned to a proctored exam or one of three types of unproctored exam. Students who took unproctored exams cheated significantly more, which suggests that it may be premature to implement this approach in college classrooms. These findings point to the importance of conducting ecologically valid and well-controlled field studies that translate psychological theory into practice when introducing large-scale educational reforms.

The entrainment interface

1972 ◽  
Vol 51 (1) ◽  
pp. 97-118 ◽  
Author(s):  
O. M. Phillips
Keyword(s):  
Velocity Field ◽  
Turbulent Flow ◽  
Surface Area ◽  
Large Scale ◽  
Positive Curvature ◽  
Lagrangian Description ◽  
Eulerian Description ◽  
Entrainment Process ◽  
Necessary And Sufficient ◽  
Small Disturbances

A theory is developed to describe the evolution of the entrainment interface in turbulent flow, in which the surface is convoluted by the large-scale eddies of the motion and at the same time advances relative to the fluid as a result of the micro-scale entrainment process. A pseudo-Lagrangian description of the process indicates that the interface is characterized by the appearance of ‘billows’ of negative curvature, over which surface area is, on average, being generated, separated by re-entrant wedges (lines of very large positive curvature) where surface area is consumed. An alternative Eulerian description allows calculation of the development of the interfacial configuration when the velocity field is prescribed. Several examples are considered in which the prescribed velocity field in the z direction is of the general form w = Wf(x – Ut), where the maximum value of the function f is unity. These indicate the importance of leading points on the surface which are such that small disturbances in the vicinity will move away from the point in all directions. The necessary and sufficient condition for the existence of one or more leading points on the surface is that U [les ] V, the speed of advance of an element of the surface relative to the fluid element at the same point. The existence of leading points is accompanied by the appearance of line discontinuities in the surface slope re-entrant wedges, In these circumstances, the overall speed of advance of the convoluted surface is found to be W + (V2 – U2)½, where W is the maximum outwards velocity in the region; this result is independent of the distribution f.When the speed U with which an ‘eddy’ moves relative to the outside fluid is greater than the speed of advance V of an element of the front, the interface develops neither leading points nor discontinuities in slope; the amplitude of the surface convolutions and the overall entrainment speed are both reduced greatly. In a turbulent flow, therefore, the large-scale motions influencing entrainment are primarily those that move slowly relative to the outside fluid (with relative speed less than V). The experimental results of Kovasznay, Kibens & Blackwelder (1970) are reviewed in the light of these conclusions. It appears that in their experiments the entrainment speed V is of the order fifteen times the Kolmogorov velocity, the large constant of proportionality being apparently the result of augmentation by micro-convolutions of the interface associated with small and meso-scale eddies of the turbulence.

Surface area controlled heterogeneous nucleation

2012 ◽  
Vol 136 (5) ◽  
pp. 054704 ◽  
Author(s):  
Brian Steer ◽  
Boris Gorbunov ◽  
Jonathan Rowles ◽  
David Green
Keyword(s):  
Surface Area ◽  
Heterogeneous Nucleation

scholarly journals Robust simulation of mineral precipitation–dissolution problems with variable mineral surface area

2021 ◽  
Vol 129 (1) ◽  
Author(s):  
Serge Kräutle ◽  
Jan Hodai ◽  
Peter Knabner
Keyword(s):  
Surface Area ◽  
Ad Hoc ◽  
Chemical Species ◽  
Special Focus ◽  
Proof Of Concept ◽  
Mineral Surface ◽  
Mineral Precipitation ◽  
Numerical Tests ◽  
Ill Posed ◽  
Mineral Surface Area

AbstractWe consider a macroscale model of transport and reaction of chemical species in a porous medium with a special focus on mineral precipitation–dissolution processes. In the literature, it is frequently proposed that the reaction rate should depend on the reactive mineral surface area, and so on the amount of mineral. We point out that a frequently used model is ill posed in the sense that it admits non-unique solutions. We investigate what consequences this non-uniqueness has on the numerical solution of the model. The main novelty in this article is our proposal of a certain substitution which removes the ill-posedness from the system and which leads to better numerical results than some “ad hoc methods.” We think that the proposed substitution is a rather elegant way to get rid of the non-uniqueness and the numerical difficulties and is much less technical than other ideas. As a proof of concept, we present some numerical tests and simulations for the new model.

scholarly journals Large-scale grid integration of residential thermal energy storages as demand-side flexibility resource: A review of international field studies

2019 ◽  
Vol 101 ◽  
pp. 527-547 ◽  
Author(s):  
Peter Kohlhepp ◽  
Hassan Harb ◽  
Henryk Wolisz ◽  
Simon Waczowicz ◽  
Dirk Müller ◽  
...  
Keyword(s):  
Thermal Energy ◽  
Large Scale ◽  
Field Studies ◽  
Grid Integration ◽  
Demand Side ◽  
Large Scale Grid ◽  
Scale Grid

Facile and large-scale synthesis of poly(m-phenylenediamine) nanobelts with high surface area and superior dye adsorption ability

RSC Advances ◽  
2014 ◽  
Vol 4 (85) ◽  
pp. 45244-45250 ◽  
Author(s):  
Yun Meng ◽  
Liyuan Zhang ◽  
Liyuan Chai ◽  
Wanting Yu ◽  
Ting Wang ◽  
...  
Keyword(s):  
Surface Area ◽  
Large Scale ◽  
High Surface ◽  
High Surface Area ◽  
Dye Adsorption ◽  
High Adsorption ◽  
Adsorption Ability ◽  
Adsorption Performance ◽  
Large Scale Synthesis

PmPD nanobelts with high adsorption performance have been synthesized by using CTAP as oxidants.

scholarly journals Modeling the regional impact of ship emissions on NO<sub>x</sub> and ozone levels over the Eastern Atlantic and Western Europe using ship plume parameterization

2010 ◽  
Vol 10 (14) ◽  
pp. 6645-6660 ◽  
Author(s):  
P. Huszar ◽  
D. Cariolle ◽  
R. Paoli ◽  
T. Halenka ◽  
M. Belda ◽  
...  
Keyword(s):  
Large Scale ◽  
Western Europe ◽  
Surface Ozone ◽  
Chemical Species ◽  
Nitrogen Monoxide ◽  
Ozone Production ◽  
Nox Emissions ◽  
Ship Emissions ◽  
Concentrated Source ◽  
The Impact

Abstract. In general, regional and global chemistry transport models apply instantaneous mixing of emissions into the model's finest resolved scale. In case of a concentrated source, this could result in erroneous calculation of the evolution of both primary and secondary chemical species. Several studies discussed this issue in connection with emissions from ships and aircraft. In this study, we present an approach to deal with the non-linear effects during dispersion of NOx emissions from ships. It represents an adaptation of the original approach developed for aircraft NOx emissions, which uses an exhaust tracer to trace the amount of the emitted species in the plume and applies an effective reaction rate for the ozone production/destruction during the plume's dilution into the background air. In accordance with previous studies examining the impact of international shipping on the composition of the troposphere, we found that the contribution of ship induced surface NOx to the total reaches 90% over remote ocean and makes 10–30% near coastal regions. Due to ship emissions, surface ozone increases by up to 4–6 ppbv making 10% contribution to the surface ozone budget. When applying the ship plume parameterization, we show that the large scale NOx decreases and the ship NOx contribution is reduced by up to 20–25%. A similar decrease was found in the case of O3. The plume parameterization suppressed the ship induced ozone production by 15–30% over large areas of the studied region. To evaluate the presented parameterization, nitrogen monoxide measurements over the English Channel were compared with modeled values and it was found that after activating the parameterization the model accuracy increases.

scholarly journals Improved techniques for liquid culture of human and mouse bone marrow

Blood ◽  
1976 ◽  
Vol 47 (3) ◽  
pp. 369-379
Author(s):  
MJ Cline ◽  
DW Golde
Keyword(s):  
Bone Marrow ◽  
Stem Cell ◽  
Large Scale ◽  
Membrane Surface ◽  
Diffusion Chamber ◽  
Mononuclear Phagocytes ◽  
Mouse Bone Marrow ◽  
Improved Performance ◽  
Proliferation In Vitro

Previous studies using the in vitro diffusion chamber (Marbrook) have shown that bone marrow grown in this system will undergo limited stem cell replication and differentiation to mature granulocytes and mononuclear phagocytes. A series of studies with modified culture systems was initiated to improve cell production and committed stem cell (CFU-C) proliferation in vitro. Introduction of a continuous-flow system and a migration technique providing means of egress for mature neutrophils resulted in substantially improved performance. CFU-C were found to be capable of migration through a 3-mu pore membrane. These studies indicated that membrane surface area, culture medium circulation, and mature cell egress were among the conditions that could be optimized for maximum hematopoietic cell proliferation in suspension culture. The present observations also suggested that large- scale in vitro growth of mammalian bone marrow may be feasible.

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