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We investigate the internal flow pattern of an evaporating droplet using tomographic particle image velocimetry (PIV) when the contact line non-uniformly recedes. We observe a three-dimensional azimuthal vortex pair while the contact line non-uniformly recedes and the symmetry-breaking flow field is maintained during the evaporation. Based on the experimental results, we show that the vorticity magnitude of the internal flow is related to the relative contact line motion. Furthermore, to explain how the azimuthal vortex pair flow is created, we develop a theoretical model by taking into account the relation between the contact line motion and evaporating flux. Finally, we show that the theoretical model has a good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Background: Caesarean section (C-section) rates are often low among the poor and very high among the better-off in low- and middle-income countries. We examined to what extent these differences are explained by medical need in an African context. Methods: We analyzed electronic records of 12,209 women who gave birth in a teaching hospital in Kenya in 2014. C-section rates were calculated by socioeconomic position (SEP), using maternal occupation (professional, small business, housewife, student) as indicator. We assessed if women had documented clinical indications according to hospital guidelines and if socioeconomic differences in C-section rates were explained by indication. Results: Indication for C-section according to hospital guidelines was more prevalent among professionals than housewives (16% vs. 9% of all births). The C-section rate was also higher among professionals than housewives (21.1% vs. 15.8% [OR 1.43; 95%CI 1.23–1.65]). This C-section rate difference was largely explained by indication (4.7 of the 5.3 percentage point difference between professionals and housewives concerned indicated C-sections, often with previous C-section as indication). Repeat C-sections were near-universal (99%). 43% of primary C-sections had no documented indication. Over-use was somewhat higher among professionals than housewives (C-section rate among women without indication: 6.6 and 5.5% respectively), which partly explained socioeconomic differences in primary C-section rate. Conclusions: Socioeconomic differences in C-section rates can be largely explained by unnecessary primary C-sections and higher supposed need due to previous C-section. Prevention of unnecessary primary C-sections and promoting safe trial of labor should be priorities in addressing C-section over-use and reducing inequalities. Unnecessary primary C-sections and ubiquitous repeat C-sections drive overall C-section rates and C-section inequalities. [ABSTRACT FROM AUTHOR]

ABSTRACT Cell assemblies code information in both the temporal and spatial domain. One tractable example of temporal coding is the phenomenon of phase precession. In medial entorhinal cortex, theta-phase precession is observed in spatially specific grid cells, with grid spike-times shifting to earlier phases of the extracellular theta rhythm as the animal passes through the grid field. Although the exact mechanisms underlying spatial-temporal coding remain unknown, computational work points to single-cell oscillatory activity as a biophysical mechanism capable of producing phase precession. Support for this idea comes from observed correlations between single-cell resonance and entorhinal neurons characterized by phase precession. Here, we take advantage of the absence of single-cell theta-frequency resonance in hyperpolarization-activated cyclic nucleotide-gated (HCN) 1 knockout (KO) mice to examine the relationship between intrinsic rhythmicity and phase precession. We find phase precession is highly comparable between forebrain-restricted HCN1 KO and wild-type mice. Grid fields in HCN1 KO mice display more experience-dependent asymmetry however, consistent with reports of enhanced long-term potentiation in the absence of HCN1 and raising the possibility that the loss of HCN1 improves temporal coding via the rate-phase transformation. Combined, our results clarify the role of HCN1 channels in temporal coding and constrain the number of possible mechanisms generating phase precession. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A new method for the fast evaluation of photoresist residue removal efficiency is discussed in this paper. In this method "haze" which is the low-frequency component of the background signal of a light scattering instrument is mapped over the entire wafer. Since the background signal is sensitive to any kind of surface anomaly, it can be used as a metrology for any kind of surface roughness or residues. The goal of this paper is to devise a fast and cheap screening method for photoresist residue removal efficiency. Using this method we show that cleaning solutions can be easily screened for their residue removal efficiencies based on the haze signal of the light scattering instrument. [ABSTRACT FROM AUTHOR]

The increasing complexity of semiconductor devices imposes challenging requirements on particle contamination and surface damage. To meet these requirements novel surface-cleaning processes are evaluated, which combine physical energy with organic solvents. In this work, the performance of megasonic cleaning with deionized water (DIW) and N-methylpyrrolidone (NMP) was evaluated in terms of particle removal efficiency (PRE) and damage analysis. The goal was to define an optimum process window where the PRE was maximum and the damage was minimum. Particle removal and damage analysis were performed on unpatterned silicon wafers and with patterned polysilicon lines, respectively, under identical sonic power and process parameters. A comparison between these two solvents reveals that at low sonic power the particle-cleaning performances in DIW and NMP are similar. At high sonic power, in both solvents a detailed analysis of the PRE and damage indicates a non-homogeneous trend over the surface of the wafer. More particularly, in DIW higher PRE and damage are noticed towards the edge of the wafer. In NMP, the opposite trend was observed. However, an equivalent performance was obtained at a lower sonic power in case of NMP compared to DIW. Further understanding of megasonic cleaning in solvents, and an optimization of the process parameters are the key to improve the performance of megasonic cleaning in organic solvents like NMP. [ABSTRACT FROM AUTHOR]

In this paper, a simple model is presented, describing an immersion rinsing process for flat solid substrates (e.g., semi-conductor wafers). It is assumed that together with the solid a layer of processing liquid is transferred into a tank filled with rinsing liquid. The model calculates the replacement of the processing liquid with rinsing liquid as a function of th rinse time and the position in the tank. For static rinsing systems an analytical expression is readily obtained. For dynamic systems (where liquid convection plays a role) the concept of a convective boundary layer is introduced. It is assumed that within this boundary layer diffusion is the dominant transport mechanism while outside the boundary layer convection is dominant. Under these assumptions an analytical expression can also be obtained for dynamic rinsing with the thickness of the convective boundary layer as a process parameter. The resulting analytical expressions can be readily used to calculate the concentration of remaining processing liquid in the vicinity of the solid substrate as a function, of rinse time. This provides a good way to determine the efficiency of the rinsing process. Moreover, these expressions allow us to assess the effect of changes in boundary layer thickness and thus can help with the optimization of existing rinsing processes. [ABSTRACT FROM AUTHOR]

Surface forces in low-dielectric media are much less understood than those in aqueous solutions. In this work, the technique of colloidal-probe atomic force microscopy (AFM) was used to measure the force between a silica sphere and a flat silica plate in dodecane. A transient attractive force was measured, which slowly vanished during the first hour of measurements, following the characteristic dielectric relaxation time of dodecane. Subsequently, equilibrium conditions were reached. Equilibrium forces exhibited a strong dependence on the relative humidity of the environment. An attempt was made to explain the transient attractive force in terms of electrostatic interaction. [ABSTRACT FROM AUTHOR]

Background: An accurate, practical laboratory test is needed to confirm clinical diagnosis of pertussis in adults during the first 3 symptomatic weeks, when treatment is effective and transmission can be interrupted. Methods: The sensitivity and specificity of single IgA and IgG levels were assessed in a cohort study of a pertussis epidemic in 99 adults in a closed community. Sensitivities were assessed in the sera of 46 laboratory confirmed clinical pertussis cases during the first 3 weeks. Specificities were calculated in sera of 35 asymptomatic controls without clinical symptoms or laboratory confirmed infections from the same community (internal controls). We compared these specificities with the specificities of single IgA and IgG levels in 4275 external controls from a cross-section of the general Dutch population aged 21-79 years who had not coughed for more than 2 weeks in the past year, and without pertussis diagnoses. The study was done in the Netherlands when whole-cell pertussis vaccine was used in the national vaccination programme. Results: Levels of 24 U/ml for IgA and 27 U/ml for IgG gave sensitivities of 100% and 75%, respectively, in the first 2 weeks, 100% in the third week, and 97% after the fourth week. The levels were reached within 2 days after onset of increase, and remained above these levels for roughly 7.2 and 5.1 months, respectively. Specificity was 82% for IgA and 89% for IgG in the internal controls and 90% in the external controls, respectively. Conclusion: We suggest levels of 24 U/ml for IgA level and 27 U/ml (= 27 International Units (IU)/ml) for IgG as sensitive, specific, and practical for laboratory confirmation of clinical pertussis in adults in the first 3 weeks of outbreak management. [ABSTRACT FROM AUTHOR]

Objective To assess the risk of introduction of polio virus in a Cape Verdian community of Rotterdam, during the polio epidemic in Cape Verde in 2000. Methods All 225 insufficiently vaccinated 0–14-year-old Cape Verdian children ( n = 4188) and a random sample of 285 out of all 15–30-year-old Cape Verdians ( n = 5074) in Rotterdam were surveyed to assess travel behaviour and vaccination coverage. Faecal specimens were collected and sewage samples taken in neighbourhoods with a sizable Cape Verdian population for testing of polio virus. Results During the polio epidemic in Cape Verde, 10% of insufficiently vaccinated children aged 0–14 years and 17% of adults aged 15–30 years living in Rotterdam reported travelling to Cape Verde. 94.6% of Cape Verdians in Rotterdam aged 0–14 years were sufficiently vaccinated against polio, but 9 of 91 insufficiently vaccinated children had travelled to Cape Verde during the epidemic. Of those aged 15–30 years, 10% were not vaccinated against polio. In the faeces of 80 insufficiently vaccinated individuals aged 0–14 years and in 74 adults aged 15–30 years, no poliovirus was detected. Samples of sewage from six sites were negative for poliovirus. Conclusion No evidence of poliovirus infection was found in the Cape Verde population in Rotterdam despite extensive travel to the Cape Verde during the outbreak. [ABSTRACT FROM AUTHOR]

The pertussis incidence during an outbreak in a convent in The Netherlands in 1992 was higher among 75 retired (unvaccinated) nuns (60%) than among 24 staff members (8%) and was higher among 9 nuns with only a convent career (100%) than among 66 nuns who had a career outside of the convent (55%). The pertussis incidence increased with duration of social isolation but not with age. [ABSTRACT FROM AUTHOR]

Physical cleaning methods are applied in the semiconductor industry and have become increasingly challenging due to the continued scaling of semiconductors device elements. Cavitation and acoustic phenomena are known to play a fundamental role in megasonic cleaning. Hence, a better understanding of cavitation phenomena in multi-bubble systems is crucial. Here, a study on the effects of lower bulk surface tension and different O2 concentrations on the bubble activity in the megahertz range is presented. A lower bulk surface tension (45 mN/m) with respect to ultra pure water (72 mN/m) is obtained by adding a non-ionic surface-active agent (Triton X-100). After a thorough surfactant characterization, a Triton X-100-containing cleaning solution is investigated under pulsed and continuous acoustic fields, for different acoustic amplitudes and gas concentrations. It is demonstrated that cavitation activity, measured by means of ultraharmonic cavitation noise, is enhanced in presence of a lower surface tension, under continuous acoustic fields. In addition, cavitation measurements performed under pulsed fields reveal the existence of optimal pulse-off times, for which a maximum of activity is observed. These optimal pulse-off time values are linked to the bubble dissolution theoretical times and experimentally verified. To end, cavitation noise measurements are correlated to cleaning performance in megasonic fields by means of particle removal and damage tests on patterned wafers. A clear increase in particle removal efficiency of 78 nm SiO2 particles is obtained when Triton X-100 is employed, at the optimized process conditions. In addition, the number of defects due to cavitation bubbles is significantly reduced for lower surface tension, at particle removal efficiencies <60%. The results here reported constitute a different approach towards more efficient megasonic cleaning processes. [ABSTRACT FROM AUTHOR]

Presents a study on crystal originated particles in silicon substrates that lead to gate oxide failures in metal-oxide-semiconductor devices. Nonlinear relationship between the oxide defect density and the oxide thickness; Evaluation of gate oxide integrity for oxide thickness; Dependence of the defect density on the presence of crystal originated particles.

A study is made of the effect of dissolved CO2 on cavitation inception and activity in an ultrasound system with a sound frequency of 928 kHz. It is shown that measurable cavitation activity is completely absent at moderate acoustic power densities (≤1.7 W cm-2) when only CO2 is dissolved in ultra pure water. It is suggested that the enhanced stability of CO2 bubbles against coalescence might be the origin of the delayed cavitation inception when compared to other dissolved gases. A combination of dissolved O2 and CO2 can lead to a measurable cavitation activity at an acoustic power of 420 mW cm-2, but an increase of the dissolved CO2 level reduces, in general, the observed cavitation activity. In order to compare results with different dissolved gas concentrations, measurements are performed with acoustic pulses and the pulse off time is varied. An optimal pulse-off time exists, where a maximum of cavitation activity is observed. However, the pulse-off time interval with enhanced cavitation activity is narrowed with increasing dissolved CO2 concentrations. Again, a decrease in bubble coalescence might explain the narrowing of the “enhancement peak”. [ABSTRACT FROM AUTHOR]

A new method for the fast evaluation of photoresist residue removal efficiency is discussed in this paper. In this method “haze” which is the low frequency component of the background signal of a light scattering instrument is mapped over the entire wafer. Since, the background signal is sensitive to any kind of surface anomaly it can be used as a metric for any kind of surface roughness or residues. The goal of this work was to devise a fast and cheap screening method for photoresist residue removal efficiency. Using this method we show that cleaning solutions can be easily screened for their residue removal efficiencies based on the haze signal of the light scattering instrument. Different ion implantation conditions are checked and also different aerosol spray assisted cleaning conditions are evaluated. [ABSTRACT FROM AUTHOR]