The breakup dynamics of viscous liquid bridges on solid surfaces is studied experimentally. It is found that the dynamics bears similarities to the breakup of free liquid bridges in the viscous regime. Nevertheless, the dynamics is significantly influenced by the wettability of the solid substrate. Therefore, it is essential to take into account the interaction between the solid and the liquid, especially at the three-phase contact line. It is shown that when the breakup velocity is low and the solid surface is hydrophobic, the dominant channel of energy dissipation is likely due to thermally activated jumping of molecules, as described by the molecular kinetic theory. Nevertheless, the viscous dissipation in the bulk due to axial flow along the bridge can be of importance for long bridges. In view of this, a scaling relation for the time dependence of the minimum width of the liquid bridge is derived. For high viscosities, the scaling relation captures the time evolution of the minimum width very well. Furthermore, it is found that external geometrical constraints alter the dynamic behaviour of low and high viscosity liquid bridges in a different fashion. This discrepancy is explained by considering the dominant forces in each regime. Lastly, the morphology of the satellite droplets deposited on the surface is qualitatively compared with that of free liquid bridges.

Groups are only real, and only serve as a basis for collective action, when their members perceive them to be real. For a computational model to have analytic fidelity and predictive validity it, therefore, needs to engage with the psychological reality of groups, their internal structure, and their structuring by (and of) the social context in which they function.

Current sea-level rise partly stems from increased surface melting and meltwater runoff from the Greenland ice sheet. Multi-year snow, also known as firn, covers about 80% of the ice sheet and retains part of the surface meltwater. Since the firn cold content integrates its physical and thermal characteristics, it is a valuable tool for determining the meltwater-retention potential of firn. We use gap-filled climatological data from nine automatic weather stations in the ice-sheet accumulation area to drive a surface-energy-budget and firn model, validated against firn density and temperature observations, over the 1998–2017 period. Our results show a stable top 20 m firn cold content (CC20) at most sites. Only at the lower-elevation Dye-2 site did CC20 decrease, by 24% in 2012, before recovering to its original value by 2017. Heat conduction towards the surface is the main process feeding CC20 at all nine sites, while CC20 reduction occurs through low-cold-content fresh-snow addition at the surface during snowfall and latent-heat release when meltwater refreezes. Our simulations suggest that firn densification, while reducing pore space for meltwater retention, increases the firn cold content, enhances near-surface meltwater refreezing and potentially sets favourable conditions for ice-slab formation.

The objective of the present work was to evaluate the behavior of osteogenesis of mesenchymal stem cells (MSCs) on a double-layer, protective, and bioactive hybrid coating sterilized by 3 different processes: steam autoclave, hydrogen peroxide plasma, and ethylene oxide. The hybrid coating was obtained from a sol consisting of the silane precursors tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES), applied on a Ti6Al4V substrate. To promote bioactivity, hydroxyapatite (HA) particles were dispersed in a second coating (bioactive layer: TEOS/MTES + HA) applied on the first (TEOS/MTES). The sterilized coatings were evaluated by scanning electron microscopy, wettability, and micrometer roughness. The behavior of hydrolytic degradation was evaluated by the mass variation of the samples and the release of silicon by the technique of high-resolution atomic absorption spectrometry. All coatings presented morphological and superficial alterations after sterilization. Sterilization by ethylene oxide and hydrogen peroxide plasma intensified the hydrolytic degradation of the bioactive coating causing a greater release of silicon. The sterilized hybrid coatings did not show cytotoxicity to MSCs. Adhesion, viability, and osteogenic differentiation were favored on the sterilized coating of hydrogen peroxide plasma, which is opposite to what was observed for the ethylene oxide-sterilized coating.

The role that vitamin D plays in pulmonary function remains uncertain. Epidemiological studies reported mixed findings for serum 25-hydroxyvitamin D (25(OH)D)–pulmonary function association. We conducted the largest cross-sectional meta-analysis of the 25(OH)D–pulmonary function association to date, based on nine European ancestry (EA) cohorts (n 22 838) and five African ancestry (AA) cohorts (n 4290) in the Cohorts for Heart and Aging Research in Genomic Epidemiology Consortium. Data were analysed using linear models by cohort and ancestry. Effect modification by smoking status (current/former/never) was tested. Results were combined using fixed-effects meta-analysis. Mean serum 25(OH)D was 68 (sd 29) nmol/l for EA and 49 (sd 21) nmol/l for AA. For each 1 nmol/l higher 25(OH)D, forced expiratory volume in the 1st second (FEV1) was higher by 1·1 ml in EA (95 % CI 0·9, 1·3; P<0·0001) and 1·8 ml (95 % CI 1·1, 2·5; P<0·0001) in AA (Prace difference=0·06), and forced vital capacity (FVC) was higher by 1·3 ml in EA (95 % CI 1·0, 1·6; P<0·0001) and 1·5 ml (95 % CI 0·8, 2·3; P=0·0001) in AA (Prace difference=0·56). Among EA, the 25(OH)D–FVC association was stronger in smokers: per 1 nmol/l higher 25(OH)D, FVC was higher by 1·7 ml (95 % CI 1·1, 2·3) for current smokers and 1·7 ml (95 % CI 1·2, 2·1) for former smokers, compared with 0·8 ml (95 % CI 0·4, 1·2) for never smokers. In summary, the 25(OH)D associations with FEV1 and FVC were positive in both ancestries. In EA, a stronger association was observed for smokers compared with never smokers, which supports the importance of vitamin D in vulnerable populations.

Horizontal variation of landfast sea-ice properties was studied in the Gulf of Bothnia, Baltic Sea, during March 2004. In order to estimate their variability among and within different spatial levels, 72 ice cores were sampled on five spatial scales (with spacings of 10 cm, 2.5 m, 25 m, 250m and 2.5 km) using a hierarchical sampling design. Entire cores were melted, and bulk-ice salinity, concentrations of chlorophyll a (Chl a), phaeophytin (Phaeo), dissolved nitrate plus nitrite (DIN) as well as dissolved organic carbon (DOC) and nitrogen (DON) were determined. All sampling sites were covered by a 5.5–23 cm thick layer of snow. Ice thicknesses of cores varied from 26 to 58 cm, with bulk-ice salinities ranging between 0.2 and 0.7 as is typical for Baltic Sea ice. Observed values for Chl a (range: 0.8–6.0 mg Chl a L–1; median: 2.9 mg Chl a L–1) and DOC (range: 37–397 μM; median: 95 μM) were comparable to values reported by previous sea-ice studies from the Baltic Sea. Analysis of variance among different spatial levels revealed significant differences on the 2.5km scale for ice thickness, DOC and Phaeo (with the latter two being positively correlated with ice thickness). For salinity and Chl a, the 250 m scale was found to be the largest scale where significant differences could be detected, while snow depth only varied significantly on the 25 m scale. Variability on the 2.5 m scale contributed significantly to the total variation for ice thickness, salinity, Chl a and DIN. In the case of DON, none of the investigated levels exhibited variation that was significantly different from the considerable amount of variation found between replicate cores. Results from a principal component analysis suggest that ice thickness is one of the main elements structuring the investigated ice habitat on a large scale, while snow depth, nutrients and salinity seem to be of secondary importance.

Snowmelt regions on Greenland ice are mapped daily with the SeaWinds wideswath Ku-band (13.4 GHz) scatterometer on the QuikSCAT satellite. The approach exploits the high temporal resolution of SeaWinds/QuikSCAT data for the melt mapping using diurnal backscatter change independent of the absolute calibration. The results reveal several pronounced melting and refreezing events, and effects of topography are evident in the melt patterns. The spatial resolution is sufficient to identify melt features on the Sukker-toppen Iskappe west of the main ice sheet. An anomalous warming event, caused by down-ward mixing of warm air, is detected in late September 1999 over the west flank of the southern Greenland ice sheet. Time-series images of melt regions are presented over the period from summer to the fall freeze-up. The satellite observations are verified with in situ measurements from the Greenland Climate Network stations.

The steep increase in Greenland’s glacial earthquake activity detected by the Global Seismographic Network since the late 1990s suggests that a close inspection of these events might provide clues to the nature and origin of such seismic activity. Here we discuss the detection of large, unexpected seismic events of extraordinarily long duration (10–40 min) occurring about once every 2 days, and localized in the ice stream that feeds the Earth’s fastest-moving glacier (Jakobshavn Isbræ) from the east. These ‘glacial rumblings’ represent an ice-mass wasting process that is greater and more frequent than glacial earthquakes have suggested. Probably triggered by calving, the rumblings are all very similar regardless of duration, and all end with a sharp, earthquake-like event in which the largest seismic amplitude is in the rumbling and that might signal the collapse of large ice masses upstream. By calculating the total amount of seismic energy released as rumblings, we estimate that the maximum seasonal amount of ice moved seismogenically down the ice stream is up to 12 km3, or ∼30% of the average annual iceberg discharge in Jakobshavn.

Deriving glacier outlines from satellite data has become increasingly popular in the past decade. In particular when glacier outlines are used as a base for change assessment, it is important to know how accurate they are. Calculating the accuracy correctly is challenging, as appropriate reference data (e.g. from higher-resolution sensors) are seldom available. Moreover, after the required manual correction of the raw outlines (e.g. for debris cover), such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied. Here we compare outlines for clean and debris-covered glaciers, as derived from single and multiple digitizing by different or the same analysts on very high- (1 m) and medium-resolution (30 m) remote-sensing data, against each other and to glacier outlines derived from automated classification of Landsat Thematic Mapper data. Results show a high variability in the interpretation of debris-covered glacier parts, largely independent of the spatial resolution (area differences were up to 30%), and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain (differences ∼5%). The differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts. Based on these results, we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts (e.g. debris cover, shadow).

Profiles of the ice cover in the North Water area were obtained in the winter of 1980/81 by using low-level infrared thermometry. The flight measurements were carried out from December to March. The statistical analysis of the sea ice surface temperature was carried out to yield distributions, frequencies and widths of fractures. Ice-free as well as ice-covered fractures with a maximum ice thickness of 0.4 m were analysed. Typical fracture frequencies were 0.25 per km for Lancaster Sound and 0.14 per km for Baffin Bay and the North Water area, with 90% of fractures being less than 0.6 km wide. From December to March, the fractures occupied 8.8% of the Ice cover in the North Water area, 8.7% along the Baffin Bay profile and 10% in the Lancaster Sound. In the North Water area the distance (y) between fractures for different fracture widths (x) is an exponential function of the form y=Aexp(ax) (A,a are constants), for fractures between 50 and 800 m wide. In the North Water area during winter, fractures of all widths occur 5 times more frequently than in M’Clure Strait and about 7 times more frequently than in southern Beaufort Sea. The heat loss in Lancaster Sound at the ice-air interface was found to be 40 to 100% larger due to the fractures compared to a fast ice situation in the same winter.

An ice-surface temperature retrieval algorithm for the Greenland ice sheet was developed using NOAA 11 thermal radiances from channels 4 and 5. Temperature, pressure and humidity profiles, cloud observations and skin temperatures from the Swiss Federal Institute of Technology (ETH) camp, located at the equilibrium line altitude at 49°17′W, 69°34′N, were used in the LOWTRAN 7 model. Through a statistical analysis of daily clear sky profiles, the coefficients that correct for the atmospheric effects were determined for the ETH-Camp field season (May to August). Surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0.6 K. The NOAA 11 narrow-band planetary albedo values for channels 1 and 2 were calculated using pre-launch calibration coefficients. Scattering and absorption by the atmosphere were modelled with LOWTRAN 7. Then, narrow-band albedo values for the AVHRR visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements. In the visible band (580–680 nm), AVHRR-derived narrow-band albedo and the in situ measurements corrected with radiative transfer model LOWTRAN 7 showed a difference of less than 2%. For the near infrared channel (725–1100 nm) the difference between the measured and modelled narrow-band albedo was 14%. These discrepancies could be either the result of inaccurate aerosol scattering modelling (lack of the in situ observation), or the result of sensor drift due to degradation.

The third symposium on Remote Sensing of Snow and Ice, organized by the International Glaciological Society, took place in Boulder, Colorado, 17–22 May 1992. As part of this meeting a total of 21 papers was presented on snow and ice applications of Advanced Very High Resolution Radiometer (AVHRR) satellite data in polar regions. Also during this meeting a NASA sponsored Workshop was held to review the status of polar surface measurements from AVHRR. In the following we have summarized the ideas and recommendations from the workshop, and the conclusions of relevant papers given during the regular symposium sessions. The seven topics discussed include cloud masking, ice surface temperature, narrow-band albedo, ice concentration, lead statistics, sea-ice motion and ice-sheet studies with specifics on applications, algorithms and accuracy, following recommendations for future improvements. In general, we can affirm the strong potential of AVHRR for studying sea ice and snow covered surfaces, and we highly recommend this satellite data set for long-term monitoring of polar process studies. However, progress is needed to reduce the uncertainty of the retrieved parameters for all of the above mentioned topics to make this data set useful for direct climate applications such as heat balance studies and others. Further, the acquisition and processing of polar AVHRR data must become better coordinated between receiving stations, data centers and funding agencies to guarantee a long-term commitment to the collection and distribution of high quality data.

North Water is situated in the high Arctic between Greenland and Canada (74°-79°N, 70°-78°W) The sea surface of this region has no homogeneous ice cover during the winter and spring months, due to the occurrence of polynyas

The results of the heat balance and the airborne remote sensing over North Water during winter are reported The heat balance investigation was concerned with the identification of heat sources and their magnitudes The remote sensing was aimed at determining the sea surface temperature and clarifying the exact nature of the surface of North Water in winter

North Water was found to be mostly covered with new and young ice and probably devoid of first year ice until March The surface was about 20 °C warmer than that of the surrounding fast ice The warmest areas were frequently located in Smith Sound, Lady Ann Strait and around the Carey Islands Open water patches above freezing point, ranging from -1 5°C to -0 1 °C were often found along the west coast of Greenland

The surface of North Water receives heat from the sea water during winter between October and March at the rate of 15 MJm^d”1 of which 80% and 20% are from enthalpy contained in sea water and latent heat of fusion released as the surface water freezes, respectively. The basic difference in winter heat balance between North Water and other ice covered arctic seas is the magnitude of the enthalpy supplied by the seawater which is 9 MJn-2d-1 larger for the North Water This is the main heat source, which keeps the surface from becoming solidly frozen