scholarly journals Observing the formation of ice and organic crystals in active sites

2016 ◽  
Vol 114 (5) ◽  
pp. 810-815 ◽  
Author(s):  
James M. Campbell ◽  
Fiona C. Meldrum ◽  
Hugo K. Christenson
Keyword(s):  
Atmospheric Aerosols ◽  
Active Sites ◽  
High Performance ◽  
Ice Nucleation ◽  
Bulk Crystal ◽  
Cloud Formation ◽  
Organic Crystals ◽  
Crystal Deposition ◽  
Wide Range ◽  
Key Factor

Heterogeneous nucleation is vital to a wide range of areas as diverse as ice nucleation on atmospheric aerosols and the fabrication of high-performance thin films. There is excellent evidence that surface topography is a key factor in directing crystallization in real systems; however, the mechanisms by which nanoscale pits and pores promote nucleation remain unclear. Here, we use natural cleavage defects on Muscovite mica to investigate the activity of topographical features in the nucleation from vapor of ice and various organic crystals. Direct observation of crystallization within surface pockets using optical microscopy and also interferometry demonstrates that these sharply acute features provide extremely effective nucleation sites and allows us to determine the mechanism by which this occurs. A confined phase is first seen to form along the apex of the wedge and then grows out of the pocket opening to generate a bulk crystal after a threshold saturation has been achieved. Ice nucleation proceeds in a comparable manner, although our resolution is insufficient to directly observe a condensate before the growth of a bulk crystal. These results provide insight into the mechanism of crystal deposition from vapor on real surfaces, where this will ultimately enable us to use topography to control crystal deposition on surfaces. They are also particularly relevant to our understanding of processes such as cirrus cloud formation, where such topographical features are likely candidates for the “active sites” that make clay particles effective nucleants for ice in the atmosphere.

scholarly journals Tuning ice nucleation with counterions on polyelectrolyte brush surfaces

2016 ◽  
Vol 2 (6) ◽  
pp. e1600345 ◽  
Author(s):  
Zhiyuan He ◽  
Wen Jun Xie ◽  
Zhenqi Liu ◽  
Guangming Liu ◽  
Zuowei Wang ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Simulation Analysis ◽  
Specific Effect ◽  
Ice Nucleation ◽  
Dynamics Simulation ◽  
Cloud Formation ◽  
Water Molecules ◽  
Water Interface ◽  
Polyelectrolyte Brush ◽  
Wide Range

Heterogeneous ice nucleation (HIN) on ionic surfaces is ubiquitous in a wide range of atmospheric aerosols and at biological interfaces. Despite its great importance in cirrus cloud formation and cryopreservation of cells, organs, and tissues, it remains unclear whether the ion-specific effect on ice nucleation exists. Benefiting from the fact that ions at the polyelectrolyte brush (PB)/water interface can be reversibly exchanged, we report the effect of ions on HIN on the PB surface, and we discover that the distinct efficiency of ions in tuning HIN follows the Hofmeister series. Moreover, a large HIN temperature window of up to 7.8°C is demonstrated. By establishing a correlation between the fraction of ice-like water molecules and the kinetics of structural transformation from liquid- to ice-like water molecules at the PB/water interface with different counterions, we show that our molecular dynamics simulation analysis is consistent with the experimental observation of the ion-specific effect on HIN.

scholarly journals Experimental methodology and procedure for SAPPHIRE:a Semi-automatic APParatus for High-voltage Ice nucleation REsearch

2020 ◽  
Author(s):  
Jens-Michael Löwe ◽  
Markus Schremb ◽  
Volker Hinrichsen ◽  
Cameron Tropea
Keyword(s):  
Electric Field ◽  
High Voltage ◽  
Surface Defects ◽  
Ice Nucleation ◽  
Experimental Methodology ◽  
Cloud Formation ◽  
Crystal Formation ◽  
Strong Impact ◽  
Wide Range ◽  
Accuracy And Repeatability

Abstract. Ice nucleation is of great interest for various processes such as cloud formation in the scope of atmospheric research, and icing of airplanes, ships or structures. Ice nucleation research aims to improve the knowledge about the physical mechanisms and, therefore improve the safety and reliability of the applications affected by ice nucleation. Several influencing factors like liquid supercooling or contamination with nucleants, as well as external disturbances such as an electric field or surface defects affect ice nucleation. Especially for ice crystal formation in clouds and icing of high-voltage equipment, an external electric field may have a strong impact on ice nucleation. Although ice nucleation has been widely investigated for numerous conditions, the effect of an electric field on nucleation is not yet completely understood; results reported in literature are even contradictory. In the present study, an advanced experimental approach for the examination of ice nucleation in water droplets exposed to an electric field is demonstrated. It comprises a method for droplet ensemble preparation and an experimental setup, which allows observation of the droplet ensemble during its exposure to well-defined thermal and electric fields, which are both variable over a wide range. The entire approach aims at maximizing the accuracy and repeatability of the experiments in order to enable examination of even the most minor influences on ice nucleation. For that purpose, the boundary conditions the droplet sample is exposed to during the experiment are examined in particular detail using experimental and numerical methods. The methodological capabilities and accuracy have been demonstrated based on several test nucleation experiments without an electric field, indicating almost perfect repeatability.

scholarly journals A Grey-Box Ensemble Model Exploiting Black-Box Accuracy and White-Box Intrinsic Interpretability

Algorithms ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 17 ◽  
Author(s):  
Emmanuel Pintelas ◽  
Ioannis E. Livieris ◽  
Panagiotis Pintelas
Keyword(s):  
Machine Learning ◽  
Real World ◽  
High Performance ◽  
Black Box ◽  
Box Model ◽  
Proposed Model ◽  
Wide Range ◽  
Critical Issues ◽  
Key Factor ◽  
Real World Datasets

Machine learning has emerged as a key factor in many technological and scientific advances and applications. Much research has been devoted to developing high performance machine learning models, which are able to make very accurate predictions and decisions on a wide range of applications. Nevertheless, we still seek to understand and explain how these models work and make decisions. Explainability and interpretability in machine learning is a significant issue, since in most of real-world problems it is considered essential to understand and explain the model’s prediction mechanism in order to trust it and make decisions on critical issues. In this study, we developed a Grey-Box model based on semi-supervised methodology utilizing a self-training framework. The main objective of this work is the development of a both interpretable and accurate machine learning model, although this is a complex and challenging task. The proposed model was evaluated on a variety of real world datasets from the crucial application domains of education, finance and medicine. Our results demonstrate the efficiency of the proposed model performing comparable to a Black-Box and considerably outperforming single White-Box models, while at the same time remains as interpretable as a White-Box model.

scholarly journals High-speed imaging of ice nucleation in water proves the existence of active sites

2019 ◽  
Vol 5 (2) ◽  
pp. eaav4316 ◽  
Author(s):  
Mark A. Holden ◽  
Thomas F. Whale ◽  
Mark D. Tarn ◽  
Daniel O’Sullivan ◽  
Richard D. Walshaw ◽  
...  
Keyword(s):  
High Speed ◽  
Active Sites ◽  
Complex Problem ◽  
Ice Nucleation ◽  
Crystal Formation ◽  
High Speed Imaging ◽  
Wide Range ◽  
Nanoscale Topography ◽  
Salient Factor ◽  
And Control

Understanding how surfaces direct nucleation is a complex problem that limits our ability to predict and control crystal formation. We here address this challenge using high-speed imaging to identify and quantify the sites at which ice nucleates in water droplets on the two natural cleavage faces of macroscopic feldspar substrates. Our data show that ice nucleation only occurs at a few locations, all of which are associated with micron-size surface pits. Similar behavior is observed on α-quartz substrates that lack cleavage planes. These results demonstrate that substrate heterogeneities are the salient factor in promoting nucleation and therefore prove the existence of active sites. We also provide strong evidence that the activity of these sites derives from a combination of surface chemistry and nanoscale topography. Our results have implications for the nucleation of many materials and suggest new strategies for promoting or inhibiting nucleation across a wide range of applications.

scholarly journals Bacteria in the ECHAM5-HAM global climate model

2012 ◽  
Vol 12 (18) ◽  
pp. 8645-8661 ◽  
Author(s):  
A. Sesartic ◽  
U. Lohmann ◽  
T. Storelvmo
Keyword(s):  
Active Sites ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Liquid Water Path ◽  
Water Path ◽  
Ice Nuclei ◽  
Ice Water

Abstract. Some bacteria are among the most active ice nuclei found in nature due to the ice nucleation active proteins on their surface, which serve as active sites for ice nucleation. Their potential impact on clouds and precipitation is not well known and needs to be investigated. Bacteria as a new aerosol species were introduced into the global climate model (GCM) ECHAM5-HAM. The inclusion of bacteria acting as ice nuclei in a GCM leads to only minor changes in cloud formation and precipitation on a global level, however, changes in the liquid water path and ice water path are simulated, specifically in the boreal regions where tundra and forests act as sources of bacteria. Although bacteria contribute to heterogeneous freezing, their impact is reduced by their low numbers compared to other heterogeneous IN. This result confirms the outcome of several previous studies.

scholarly journals Experimental methodology and procedure for SAPPHIRE: a Semi-automatic APParatus for High-voltage Ice nucleation REsearch

2021 ◽  
Vol 14 (1) ◽  
pp. 223-238 ◽  
Author(s):  
Jens-Michael Löwe ◽  
Markus Schremb ◽  
Volker Hinrichsen ◽  
Cameron Tropea
Keyword(s):  
Electric Field ◽  
High Voltage ◽  
Surface Defects ◽  
Ice Nucleation ◽  
Experimental Methodology ◽  
Cloud Formation ◽  
Crystal Formation ◽  
Strong Impact ◽  
Wide Range ◽  
Accuracy And Repeatability

Abstract. Ice nucleation is of great interest for various processes such as cloud formation in the scope of atmospheric physics, and icing of airplanes, ships, or structures. Ice nucleation research aims to improve the knowledge about the physical mechanisms and to ensure the safety and reliability of the respective applications. Several influencing factors like liquid supercooling or contamination with nucleants, as well as external disturbances such as an electric field or surface defects, affect ice nucleation. Especially for ice crystal formation in clouds and icing of high-voltage equipment, an external electric field may also have a strong impact on ice nucleation. Although ice nucleation has been widely investigated for numerous conditions, the effect of an electric field on ice nucleation is not yet completely understood; results reported in literature are even contradictory on some issues. In the present study, an advanced experimental approach for the examination of ice nucleation in water droplets exposed to an electric field is described. It comprises a method for droplet ensemble preparation and an experimental setup, which allows observation of the droplet ensemble during its exposure to well-defined thermal and electric fields, which are both variable over a wide range. The entire approach aims at maximizing the accuracy and repeatability of the experiments in order to enable examination of even the most minor influences on ice nucleation. For that purpose, the boundary conditions the droplet sample is exposed to during the experiment are examined in particular detail using experimental and numerical methods. The methodological capabilities and accuracy have been demonstrated based on several ice nucleation experiments without an electric field, indicating almost perfect repeatability.

scholarly journals Surface charge-induced orientation of interfacial water suppresses heterogeneous ice nucleation on α-alumina (0001)

2017 ◽  
Author(s):  
Ahmed Abdelmonem ◽  
Ellen H. G. Backus ◽  
Nadine Hoffmann ◽  
M. Alejandra Sánchez ◽  
Jenée D. Cyran ◽  
...  
Keyword(s):  
Surface Charge ◽  
Atmospheric Aerosols ◽  
Molecular Level ◽  
Water Structure ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Low Ph ◽  
Cloud Formation ◽  
Interfacial Water ◽  
Heterogeneous Ice Nucleation

Abstract. Surface charge is one of the surface properties of atmospheric aerosols, which has been linked to heterogeneous ice-nucleation and hence cloud formation, microphysics and optical properties. Despite the importance of surface charge for ice nucleation, many questions remain on the molecular-level mechanisms at work. Here, we combine droplet freezing assay studies with vibrational sum frequency generation (SFG) spectroscopy to correlate interfacial water structure to surface nucleation strength. We study immersion freezing of aqueous solutions of various pHs on the atmospherically relevant aluminum oxide α-Al2O3 (0001) surface using an isolated droplet on the surface . The high pH solutions freeze at temperatures higher than that of the low pH solution while the neutral pH has the highest freezing temperature. On the molecular level, the SFG spectrum of the interfacial water changes substantially upon freezing. At all pHs, crystallization leads to a reduction of intensity of the 3400 cm−1 water resonance, while the 3200 cm−1 intensity drops for low pH but increases for neutral and high pHs. We find that charge-induced surface templating suppresses nucleation, irrespective of the sign of the surface charge. Heterogeneous nucleation is most efficient for the nominally neutral surface.

scholarly journals Surface-charge-induced orientation of interfacial water suppresses heterogeneous ice nucleation on <i>α</i>-alumina (0001)

2017 ◽  
Vol 17 (12) ◽  
pp. 7827-7837 ◽  
Author(s):  
Ahmed Abdelmonem ◽  
Ellen H. G. Backus ◽  
Nadine Hoffmann ◽  
M. Alejandra Sánchez ◽  
Jenée D. Cyran ◽  
...  
Keyword(s):  
Surface Charge ◽  
Atmospheric Aerosols ◽  
Molecular Level ◽  
Water Structure ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Low Ph ◽  
Cloud Formation ◽  
Interfacial Water ◽  
Heterogeneous Ice Nucleation

Abstract. Surface charge is one of the surface properties of atmospheric aerosols, which has been linked to heterogeneous ice nucleation and hence cloud formation, microphysics, and optical properties. Despite the importance of surface charge for ice nucleation, many questions remain on the molecular-level mechanisms at work. Here, we combine droplet-freezing assay studies with vibrational sum frequency generation (SFG) spectroscopy to correlate interfacial water structure to surface nucleation strength. We study immersion freezing of aqueous solutions of various pHs on the atmospherically relevant aluminum oxide α-Al2O3 (0001) surface using an isolated droplet on the surface. The high-pH solutions freeze at temperatures higher than that of the low-pH solution, while the neutral pH has the highest freezing temperature. On the molecular level, the SFG spectrum of the interfacial water changes substantially upon freezing. At all pHs, crystallization leads to a reduction of intensity of the 3400 cm−1 water resonance, while the 3200 cm−1 intensity drops for low pH but increases for neutral and high pHs. We find that charge-induced surface templating suppresses nucleation, irrespective of the sign of the surface charge. Heterogeneous nucleation is most efficient for the nominally neutral surface.

scholarly journals Dynamic perforation and compression tests of PMMA for a wide range of temperatures - experimental and preliminary numerical analysis

2018 ◽  
Vol 183 ◽  
pp. 02055 ◽  
Author(s):  
Maciej Klosak ◽  
Alexis Rusinek ◽  
Tomasz Jankowiak ◽  
Zakaria El Qoubba ◽  
Rodrigue Matadi Boumbimba ◽  
...  
Keyword(s):  
Strain Rate ◽  
High Performance ◽  
Experimental Tests ◽  
Fe Model ◽  
Strain Rates ◽  
Stress Evolution ◽  
Compression Tests ◽  
Wide Range ◽  
Model Predictions ◽  
Key Factor

Experimental tests were carried out on poly(Methyl Methacrylate) (PMMA) in order to define its mechanical behaviour over a wide range of temperature. To reach high strain rate, perforation tests were performed within a wide range of temperatures using a high-performance oven, from room temperature to 130 °C, above the glass transition temperature Tg. In addition, the results were confronted with compression tests previously obtained. Based on experiments, the temperature transition between fragile and ductile was defined. The material became fully ductile above 118 °C inducing no cracking and debris during the perforation process. The yield stress evolution as function of strain rate for various temperatures was modelled by using the cooperative model. The model predictions were in agreement with experimental data. Two material models developed by Richeton and Nasraoui were analysed, the latter was then implemented into the FE model to simulate perforation tests for a wide range of temperatures and strain rates. It was observed that the coupling strain rate-temperature is a key factor to predict the structure behaviour not only in terms of material behaviour but also in terms of dynamic failure.

scholarly journals Twin-plate Ice Nucleation Assay (TINA) with infrared detection for high-throughput droplet freezing experiments with biological ice nuclei in laboratory and field samples

2018 ◽  
Vol 11 (11) ◽  
pp. 6327-6337 ◽  
Author(s):  
Anna T. Kunert ◽  
Mark Lamneck ◽  
Frank Helleis ◽  
Ulrich Pöschl ◽  
Mira L. Pöhlker ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
High Throughput ◽  
Atmospheric Aerosols ◽  
Cooling System ◽  
Infrared Detector ◽  
Ice Nucleation ◽  
Cumulative Number ◽  
Ice Nuclei ◽  
Wide Range ◽  
Field Samples

Abstract. For efficient analysis and characterization of biological ice nuclei under immersion freezing conditions, we developed the Twin-plate Ice Nucleation Assay (TINA) for high-throughput droplet freezing experiments, in which the temperature profile and freezing of each droplet is tracked by an infrared detector. In the fully automated setup, a couple of independently cooled aluminum blocks carrying two 96-well plates and two 384-well plates, respectively, are available to study ice nucleation and freezing events simultaneously in hundreds of microliter-range droplets (0.1–40 µL). A cooling system with two refrigerant circulation loops is used for high-precision temperature control (uncertainty <0.2 K), enabling measurements over a wide range of temperatures (∼ 272–233 K) at variable cooling rates (up to 10 K min−1). The TINA instrument was tested and characterized in experiments with bacterial and fungal ice nuclei (IN) from Pseudomonas syringae (Snomax®) and Mortierella alpina, exhibiting freezing curves in good agreement with literature data. Moreover, TINA was applied to investigate the influence of chemical processing on the activity of biological IN, in particular the effects of oxidation and nitration reactions. Upon exposure of Snomax® to O3 and NO2, the cumulative number of IN active at 270–266 K decreased by more than 1 order of magnitude. Furthermore, TINA was used to study aqueous extracts of atmospheric aerosols, simultaneously investigating a multitude of samples that were pre-treated in different ways to distinguish different kinds of IN. For example, heat treatment and filtration indicated that most biological IN were larger than 5 µm. The results confirm that TINA is suitable for high-throughput experiments and efficient analysis of biological IN in laboratory and field samples.

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