A likely important feature of the poorly understood aerosol‐cloud interactions over the Southern Ocean (SO) is the dominant role of sea spray aerosol, versus terrestrial aerosol. Ice nucleating ...particles (INPs), or particles required for heterogeneous ice nucleation, present over the SO have not been studied in several decades. In this study, boundary layer aerosol properties and immersion freezing INP number concentrations (nINPs) were measured during a ship campaign that occurred south of Australia (down to 53°S) in March–April 2016. Ocean surface chlorophyll a concentrations ranged from 0.11 to 1.77 mg/m3, and nINPs were a factor of 100 lower than historical surveys, ranging from 0.38 to 4.6 m−3 at −20 °C. The INP population included organic heat‐stable material, with contributions from heat‐labile material. Lower INP source potentials of SO seawater samples compared to Arctic seawater were consistent with lower ice nucleating site densities in this study compared to north Atlantic air masses.
Plain Language Summary
The Southern Ocean is known for a prevalence of clouds that contain both liquid and ice, which are one of the most poorly understood cloud regimes in the climate system. A large gap in understanding important processes in these clouds is a lack of knowledge regarding particles (e.g., sea spray) required for forming ice crystals, termed ice nucleating particles. In a ship‐based monthlong field study, several instruments were deployed in efforts to characterize the ice nucleating particles present over the Southern Ocean for the first time in over four decades. Abundances of ice nucleating particles throughout the voyage were extremely low compared to other ocean regions, and concentrations were 2 orders of magnitude lower than the most recent survey conducted in the 1970s. We report that the ocean‐derived ice nucleating particles observed in this study were organic in nature, supporting a hypothesized link between ice nucleating particles and organic particles associated with phytoplankton blooms. The data from this study provide a desperately needed benchmark for constraining the number of ice crystals that may form in the remote and poorly understood clouds occurring over the Southern Ocean.
Key Points
Number concentrations of ice nucleating particles over the Southern Ocean in March 2016 were a factor of 100 lower than historical surveys
The ice nucleating particle source strength of Southern Ocean seawater was lower than previous measurements in northern hemisphere seawater
Ice nucleation site densities were lower over the Southern Ocean compared to measurements of pristine air masses from other ocean basins
Black carbon (BC) aerosol plays an important role in the Earth’s climate system because it absorbs solar radiation and therefore potentially warms the climate; however, BC can also act as a seed for ...cloud particles, which may offset much of its warming potential. If BC acts as an ice nucleating particle (INP), BC could affect the lifetime, albedo, and radiative properties of clouds containing both supercooled liquid water droplets and ice particles (mixed-phase clouds). Over 40% of global BC emissions are from biomass burning; however, the ability of biomass burning BC to act as an INP in mixed-phase cloud conditions is almost entirely unconstrained. To provide these observational constraints, we measured the contribution of BC to INP concentrations (INP) in real-world prescribed burns and wildfires. We found that BC contributes, at most, 10% to INP during these burns. From this, we developed a parameterization for biomass burning BC and combined it with a BC parameterization previously used for fossil fuel emissions. Applying these parameterizations to global model output, we find that the contribution of BC to potential INP relevant to mixed-phase clouds is ∼5% on a global average.
Black carbon (BC) aerosol plays an important role in the Earth’s climate system because it absorbs solar radiation and therefore potentially warms the climate; however, BC can also act as a seed for ...cloud particles, which may offset much of its warming potential. If BC acts as an ice nucleating particle (INP), BC could affect the lifetime, albedo, and radiative properties of clouds containing both supercooled liquid water droplets and ice particles (mixed-phase clouds). Over 40% of global BC emissions are from biomass burning; however, the ability of biomass burning BC to act as an INP in mixed-phase cloud conditions is almost entirely unconstrained. To provide these observational constraints, we measured the contribution of BC to INP concentrations (INP) in real-world prescribed burns and wildfires. We found that BC contributes, at most, 10% to INP during these burns. From this, we developed a parameterization for biomass burning BC and combined it with a BC parameterization previously used for fossil fuel emissions. Applying these parameterizations to global model output, we find that the contribution of BC to potential INP relevant to mixed-phase clouds is ~5% on a global average.
The present study aims to discover the contribution of glycosaminoglycans (GAGs) and collagen fibers to the mechanical properties of the osteoarthritic (OA) cartilage tissue. We used nanoindentation ...experiments to understand the mechanical behavior of mild and severe osteoarthritic cartilage at micro- and nano-scale at different swelling conditions. Contrast enhanced micro-computed tomography (EPIC-μCT) was used to confirm that mild OA specimens had significantly higher GAGs content compared to severe OA specimens. In micro-scale, the semi-equilibrium modulus of mild OA specimens significantly dropped after immersion in a hypertonic solution and at nano-scale, the histograms of the measured elastic modulus revealed three to four components. Comparing the peaks with those observed for healthy cartilage in a previous study indicated that the first and third peaks represent the mechanical properties of GAGs and the collagen network. The third peak shows considerably stiffer elastic modulus for mild OA samples as compared to the severe OA samples in isotonic conditions. Furthermore, this peak clearly dropped when the tonicity increased, indicating the loss of collagen (pre-) stress in the shrunk specimen. Our observations support the association of the third peak with the collagen network. However, our results did not provide any direct evidence to support the association of the first peak with GAGs. For severe OA specimens, the peak associated with the collagen network did not drop when the tonicity increased, indicating a change in the response of OA cartilage to hypertonicity, likely collagen damage, as the disease progresses to its latest stages.
Biodegradable polymeric microspheres are interesting drug delivery vehicles for site-specific sustained release of drugs used in treatment of osteoarthritis. We study the nano-mechanical properties ...of microspheres composed of hydrophilic multi-block copolymers, because the release profile of the microspheres may be dependent on the mechanical interactions between the host tissues and the microspheres that aim to incorporate between the cartilage surfaces. Three different sizes of monodisperse microspheres, namely 5, 15, and 30μm, were tested in both dry and hydrated (swollen) states. Atomic force microscopy was used for measuring nanoindentation-based force–displacement curves that were later used for calculating the Young׳s moduli using the Hertz׳s contact theory. For every microsphere size and condition, the measurements were repeated 400–500 times at different surface locations and the histograms of the Young׳s modulus were plotted. The mean Young׳s modulus of 5, 15, and 30μm microspheres were respectively 56.1±71.1 (mean±SD), 94.6±103.4, and 57.6±58.6MPa under dry conditions and 226.4±54.2, 334.5±128.7, and 342.5±136.8kPa in the swollen state. The histograms were not represented well by the average Young׳s modulus and showed three distinct peaks in the dry state and one distinct peak in the swollen state. The peaks under dry conditions are associated with the different parts of the co-polymeric material at the nano-scale. The measured mechanical properties of swollen microspheres are within the range of the nano-scale properties of cartilage, which could favor integration of the microspheres with the host tissue.
The role of marine ice-nucleating particles (INPs) in modifying clouds and radiation balance over oceans is uncertain. While recent studies have advanced our understanding of the abundance of marine ...INPs, characterizing their sources and composition remains a challenge. INP concentrations above oceans are typically low, sometimes extraordinarily so, but there is evidence of elevated levels associated with phytoplankton blooms. Mesocosm experiments have shown that ice-nucleating entities (INEs, which include discrete particles as well as ice-nucleating monolayers) are produced, and INP emissions raised, in the decay phase following bloom collapse. To test if INE production depends upon phytoplankton type, we added dead particulate biomass of a green alga (
Nannochloris atomus
), a diatom (
Skeletonema marinoi
) and a cyanobacterium (
Prochlorococcus marinus
) to a miniature Marine Aerosol Reference Tank filled with seawater. As decomposition progressed, heterotrophic bacteria initially increased and plateaued, then declined, coinciding with an increase in heterotrophic nanoflagellates (HNF) and viruses. Enzyme activities typically increased over several days before plateauing or decreasing, while humic-like substances (HULIS) steadily accumulated. INEs in the seawater peaked 3-5 days after each detritus addition, increasing ∼10- to ∼20-fold. INE concentration was closely correlated with HNF counts, viruses and the concentration of HULIS, but not with bacteria or enzyme activities. Newly-fabricated INEs were organic, primarily heat stable (95 °C), and varied in size. INP concentrations in sea spray aerosol (SSA) tended to peak shortly before the peak of INEs in the seawater, at 4-, 35- and 15-fold higher than at the start in the
N. atomus
,
S. marinoi
, and
P. marinus
incubations, respectively. Using data from the
P. marinus
incubation, we were able to provide the first estimate of INP enrichment in SSA (over its concentration in the water): it was initially ∼200× for the fresh seawater and increased further after the addition of the
P. marinus
inoculum. We also tested if a simple nutrient mix (bovine serum albumin (BSA) and three monosaccharides) could stimulate INP production: INEs in the seawater changed little, but INP emissions fell abruptly immediately upon BSA addition due to it forming a monolayer which displaced the sea surface microlayer (SML). These experiments revealed that INE production in the decay phase of a phytoplankton bloom requires the addition of a natural, complex substrate to initiate a realistic succession of decomposers, and that INP emissions are further controlled by their concentration in the SML and, indirectly, by the impact of SML composition upon jet and film drop production.
Oceans emit ice-nucleating particles (INPs) which freeze supercooled cloud droplets, modifying clouds. We added dead biomass of three phytoplankton to seawater. Each time, this stimulated INP production in the water and INP emissions in sea spray.
Application of the NOK method in sentence modelling Koch, M. Rauker; Pavlic, M.; Jakupovic, A.
2014 37th International Convention on Information and Communication Technology, Electronics and Microelectronics (MIPRO)
Conference Proceeding
Knowledge representation is one of the areas covered by artificial intelligence. One of the methods for graphical representation of text expressed knowledge is the method NOK (Nodes Of Knowledge). ...NOK method enables transformation of text expressed knowledge into a graphical network of words and group of words. In this paper application of NOK method is presented. This application is based on sentences from an Aesop's Fable in Croatian ("Golden eggs in the chicken") and English ("The Goose with the golden eggs") version. In this way the applicability of this method on two natural human languages is presented, and similarities and differences that are partially conditioned by freedom of translators, and not only by differences in the syntax of the two languages, are observed.
Use of Web 2.0 tools in teaching Gligora Markovic, M.; Rauker Koch, M.; Francic, M.
2012 Proceedings of the 35th International Convention MIPRO
Conference Proceeding
Using information and communication technology (ICT) is unavoidable in today's learning and teaching process at all levels of education, and the use of Web 2.0 tools is the evidence of it. What makes ...Web 2.0 tools very appropriate for this purpose is its availability on any computer with an Internet connection, simplicity of use, ease of communication and participant's interaction in education. The ease of communication drives students to use the tools even in their free time stimulating teamwork and creativity. Additionally, the tools are free of charge and may need only user registration and, in many cases, single computer per classroom is enough. To find out to what extent these tools are used in our educational institutions the research was conducted among teachers in the Republic of Croatia (RH) through an online survey. The research results show that majority of teachers use ICT in teaching, but mainly as Power Point presentations. The teachers use Web 2.0 tools several times a week, primarily for exchanging audio and video learning materials. In future, a lot of them plan to use Web 2.0 tools with the aim of encouraging students to increase their participation in educational process through interaction and exchange of educational materials.
PDF
