Island size distributions in submonolayer growth: successful prediction by mean field theory with coverage dependent capture numbers

We show that mean-field rate equations for submonolayer growth can successfully predict island size distributions in the pre-coalescence regime if the full dependence of capture numbers on both the island size and the coverage is taken into account. This is demonstrated by extensive Kinetic Monte Carlo simulations for a growth kinetics with hit and stick aggregation. A detailed analysis of the capture numbers reveals a nonlinear dependence on the island size for small islands. This nonlinearity turns out to be crucial for the successful prediction of the island size distribution and renders an analytical treatment based on a continuum limit of the mean-field rate equations difficult.Comment: 4 pages, 4 figue

Capture-zone scaling in island nucleation: phenomenological theory of an example of universal fluctuation behavior

In studies of island nucleation and growth, the distribution of capture zones, essentially proximity cells, can give more insight than island-size distributions. In contrast to the complicated expressions, ad hoc or derived from rate equations, usually used, we find the capture-zone distribution can be described by a simple expression generalizing the Wigner surmise from random matrix theory that accounts for the distribution of spacings in a host of fluctuation phenomena. Furthermore, its single adjustable parameter can be simply related to the critical nucleus of growth models and the substrate dimensionality. We compare with extensive published kinetic Monte Carlo data and limited experimental data. A phenomenological theory sheds light on the result.Comment: 5 pages, 4 figures, originally submitted to Phys. Rev. Lett. on Dec. 15, 2006; revised version v2 tightens and focuses the presentation, emphasizes the importance of universal features of fluctuations, corrects an error for d=1, replaces 2 of the figure

Crossover in the scaling of island size and capture zone distributions

Simulations of irreversible growth of extended (fractal and square) islands with critical island sizes i=1 and 2 are performed in broad ranges of coverage \theta and diffusion-to-deposition ratios R in order to investigate scaling of island size and capture zone area distributions (ISD, CZD). Large \theta and small R lead to a crossover from the CZD predicted by the theory of Pimpinelli and Einstein (PE), with Gaussian right tail, to CZD with simple exponential decays. The corresponding ISD also cross over from Gaussian or faster decays to simple exponential ones. For fractal islands, these features are explained by changes in the island growth kinetics, from a competition for capture of diffusing adatoms (PE scaling) to aggregation of adatoms with effectively irrelevant diffusion, which is characteristic of random sequential adsorption (RSA) without surface diffusion. This interpretation is confirmed by studying the crossover with similar CZ areas (of order 100 sites) in a model with freezing of diffusing adatoms that corresponds to i=0. For square islands, deviations from PE predictions appear for coverages near \theta=0.2 and are mainly related to island coalescence. Our results show that the range of applicability of the PE theory is narrow, thus observing the predicted Gaussian tail of CZD may be difficult in real systems.Comment: 9 pages, 7 figure

Dynamic effects on the loss of control in template-directed nucleation

Full nucleation control for deposited functional molecules on pre-patterned surfaces is of major technological relevance. To understand the nucleation behavior we combine the numerical solution for the evolution of the adatom concentration with standard nucleation theory. From the qualitative change in nucleation behavior upon variation of the pattern spacing and coverage we show why the quality of nucleation control can vary significantly in different parameter regimes. In some limits analytical expressions can be formulated for the nucleation control. Our analysis provides a theoretical explanation for previous experimental observations [Wang et al, PRL 98, 225504 (2007)]

Acceptability of intrapartum ultrasound by mothers in an African population

Intrapartum ultrasound is gaining high acceptance by many women as another method for assessing labour progression. Despite growing evidence of the effectiveness of ultrasound in labour, the acceptance of intrapartum ultrasound has not been previously investigated in black Africans. This study aimed to determine women’s acceptance of intrapartum ultrasound and their preference for transperineal ultrasound or digital vaginal examination (digital VE) in Ghana. An analytical cross-sectional study was conducted among mothers who had had both digital VE and transperineal ultrasound during labour in a tertiary hospital. Information about their sociodemographic characteristics, experience with, and preference for ultrasound or digital VE in labour using a pretested structured questionnaire was obtained. Their experiences were categorised as ‘tolerable, ‘quite uncomfortable’ or ‘very uncomfortable’. Categorical variables were compared using Fisher’s exact test. A p value < 0.05 was considered statistically significant. Altogether, 196 women were recruited into the study. The mean age of the women was 26.7 years (standard deviation, 4.6 years). Nearly half (47%) of the women had never delivered before. Significantly more women considered transperineal ultrasound to be more tolerable than digital VE (66% vs. 40%; p < 0.001). Almost all the women (97.5%) described their experience with transperineal ultrasound to be better than digital VE, and would choose transperineal ultrasound over digital VE in the future (98.5% vs. 1.5%; p < 0.001). The findings of this study are comparable to those of other related studies reported recently. This research confirms high acceptance of ultrasound in labour by mothers from different countries and across continents, implying that cultural differences do not influence women’s responses to and interest in intrapartum ultrasound. Most women found ultrasound in labour to be more tolerable than digital VE. Whenever possible, transperineal ultrasound should be provided as an alternative to digital VE during labour.N/

Adoption of practices to mitigate harvest losses − Phase 2

Patane et al. 2019 determined that Harvesting Best Practice (HBP) is predicated by two essential objectives: 1. Defining the critical point where harvesting losses can be minimised and delivered yields improved to achieve the best economic return for the grower and harvesting operation; and 2. Balancing losses with cane quality, which is determined by sound billet quality with an acceptable level of Extraneous Matter (EM). Despite significant research into the impact of higher harvester pour rates and fan speeds on harvested cane yields, use of HBP recommendations prior to the commencement of the adoption program across the industry was relatively low. Full HBP adoption across the Australian sugarcane industry could substantially increase industry revenue without the need for horizontal expansion (increase in cane land). In 2019, continuing on from the work conducted by Patane et al. (2019), Sugar Research Australia in partnership with the Queensland Department of Agriculture and Fisheries delivered further trials

The seasonal cycle of ocean-atmosphere CO2 Flux in Ryder Bay, West Antarctic Peninsula

Approximately 15 million km2 of the Southern Ocean is seasonally ice covered, yet the processes affecting carbon cycling and gas exchange in this climatically important region remain inadequately understood. Here, 3 years of dissolved inorganic carbon (DIC) measurements and carbon dioxide (CO2) fluxes from Ryder Bay on the west Antarctic Peninsula (WAP) are presented. During spring and summer, primary production in the surface ocean promotes atmospheric CO2 uptake. In winter, higher DIC, caused by net heterotrophy and vertical mixing with Circumpolar Deep Water, results in outgassing of CO2 from the ocean. Ryder Bay is found to be a net sink of atmospheric CO2 of 0.59–0.94 mol C m−2 yr−1 (average of 3 years). Seasonal sea ice cover increases the net annual CO2 uptake, but its effect on gas exchange remains poorly constrained. A reduction in sea ice on the WAP shelf may reduce the strength of the oceanic CO2 sink in this region

Intrapartum ultrasound assessment of cervical dilatation and its value in detecting active labor.

Introduction We aimed to examine the agreement between ultrasound and digital vaginal examination in assessing cervical dilatation in an African population and to assess the value of ultrasound in detecting active labor. Method A cross-sectional study was conducted in a teaching hospital in Ghana between April and September of 2016. Anterior–posterior and transverse diameters of cervical dilatation were measured with ultrasound and the mean value was compared with digital vaginal examination in 195 women in labor. Agreement between methods was examined with correlation coefficients and with Bland–Altman plots. Active labor was defined when cervix was dilated ≥ 4 cm with vaginal examinations. ROC curve analysis was conducted on the diagnostic performance of ultrasound in detecting active labor. Results Data were analyzed in 175 out of 195 (90%) cases where ultrasound could clearly visualize the cervix. The remaining 20 cases were all determined by digital vaginal examination as advanced cervical dilatation (≥ 8 cm), advanced head station (≥ + 2), and with ruptured membranes. The Pearson correlation coefficient (r) was 0.78 (95% CI 0.72–0.83) and the intra-class correlation coefficient was 0.76 (95% CI 0.69–0.81). Bland–Altman analysis obtained a mean difference of − 0.03 cm (95% CI − 0.18 to 0.12) with zero included in the CI intervals, indicating no significant difference between methods. Limits of agreement were from − 2.01 to 1.95 cm. Ultrasound predicted active labor with 0.87 (95% CI 0.75–0.99) as the area under the ROC curve. Conclusion Ultrasound measurements showed good agreement with digital vaginal examinations in assessing cervical dilatation during labor and ultrasound may be used to detect active labor.N/

Network Harmonisation of Physical Activity Variables Through Indirect Validation

Harmonisation of data for pooled analysis relies on the principle of inferential equivalence between variables from different sources. Ideally, this is achieved using models of the direct relationship with gold standard criterion measures, but the necessary validation study data are often unavailable. This study examines an alternative method of network harmonisation using indirect models. Starting methods were self-report or accelerometry, from which we derived indirect models of relationships with doubly labelled water (DLW)-based physical activity energy expenditure (PAEE) using sets of two bridge equations via one of three intermediate measures. Coefficients and performance of indirect models were compared to corresponding direct models (linear regression of DLW-based PAEE on starting methods). Indirect model beta coefficients were attenuated compared to direct model betas (10-63%), narrowing the range of PAEE values; attenuation was greater when bridge equations were weak. Directly and indirectly harmonised models had similar error variance but most indirectly derived values were biased at group-level. Correlations with DLW-based PAEE were identical after harmonisation using continuous linear but not categorical models. Wrist acceleration harmonised to DLW-based PAEE via combined accelerometry and heart rate sensing had lowest error variance (24.5%) and non-significant mean bias 0.9 (95%CI: -1.6; 3.4) kJ•day-1•kg-1. Associations between PAEE and BMI were similar for directly and indirectly harmonised values, but most fell outside the confidence interval of the criterion PAEE-to-BMI association. Indirect models can be used for harmonisation. Performance depends on the measurement properties of original data, variance explained by available bridge equations, and similarity of population characteristics.This work was funded by UK Medical Research Council (MC_UU_12015/3) and the NIHR Biomedical Research Centre in Cambridge (IS-BRC-1215-20014). UK Biobank is acknowledged for contributing to the costs of the fieldwork. Newcastle University and MedImmune are acknowledged for contributing to the costs of the doubly labelled water measurements. The funders had no role in the design, conduct, analysis, and decision to publish results from this study

Caesium on Si(100) Studied by Biassed Secondary Electron Microscopy

An ultra-high vacuum scanning electron microscope (UHV-SEM) has been used to study sub-monolayers of Cs on Si(100) surface. Cs adsorption on the surface causes a considerable change in the work function. Coverages below 1/2 monolayer (ML) have been estimated by correlating the work function changes with the secondary electron (SE) signal. It has been found that this signal is sensitive down to ~ 0.005 ML when the sample is biassed to a few hundred volts. Electron trajectories from a biassed sample have been simulated for electrons originating from different areas with different work functions across the sample. This indicates that variations in coverage can be determined by secondary electron imaging provided these coverages are less than 1/2 ML. The diffusion of Cs (\u3c 1/2 ML) above room temperature has been studied using the biassed-SE imaging technique. Observed diffusion profiles have unusual features including two linear regions. These can be explained by a model which contains two competing adsorption sites, and includes blocking of the diffusion paths by other Cs atoms