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A survey is given of experimental data on mixing in fluidized beds of small and large diameter. Two-phase theory is used to express mixing in terms of mass-transfer and dense phase eddy diffusivity.

BACKGROUND: Empirical social contact patterns are essential to understand the spread of infectious diseases. To date, no such data existed for France. Although infectious diseases are frequently seasonal, the temporal variation of contact patterns has not been documented hitherto. METHODS: COMES-F is the first French large-scale population survey, carried out over 3 different periods (February-March, April, April-May) with some participants common to the first and the last period. Participants described their contacts for 2 consecutive days, and reported separately on professional contacts when typically over 20 per day. RESULTS: 2033 participants reported 38 881 contacts (weighted median [first quartile-third quartile]: 8[5-14] per day), and 54 378 contacts with supplementary professional contacts (9[5-17]). Contrary to age, gender, household size, holidays, weekend and occupation, period of the year had little influence on the number of contacts or the mixing patterns. Contact patterns were highly assortative with age, irrespective of the location of the contact, and gender, with women having 8% more contacts than men. Although most contacts occurred at home and at school, the inclusion of professional contacts modified the structure of the mixing patterns. Holidays and weekends reduced dramatically the number of contacts, and as proxies for school closure, reduced R0 by 33% and 28%, respectively. Thus, school closures could have an important impact on the spread of close contact infections in France. CONCLUSIONS: Despite no clear evidence for temporal variation, trends suggest that more studies are needed. Age and gender were found important determinants of the mixing patterns. Gender differences in mixing patterns might help explain gender differences in the epidemiology of infectious diseases.

In India, the identity of men who have sex with men (MSM) is closely related to the role taken in anal sex (insertive, receptive or both), but little is known about sexual mixing between identity groups. Both role segregation (taking only the insertive or receptive role) and the extent of assortative (within-group) mixing are known to affect HIV epidemic size in other settings and populations. This study explores how different possible mixing scenarios, consistent with behavioural data collected in Bangalore, south India, affect both the HIV epidemic, and the impact of a targeted intervention. Deterministic models describing HIV transmission between three MSM identity groups (mostly insertive Panthis/Bisexuals, mostly receptive Kothis/Hijras and versatile Double Deckers), were parameterised with behavioural data from Bangalore. We extended previous models of MSM role segregation to allow each of the identity groups to have both insertive and receptive acts, in differing ratios, in line with field data. The models were used to explore four different mixing scenarios ranging from assortative (maximising within-group mixing) to disassortative (minimising within-group mixing). A simple model was used to obtain insights into the relationship between the degree of within-group mixing, R0 and equilibrium HIV prevalence under different mixing scenarios. A more complex, extended version of the model was used to compare the predicted HIV prevalence trends and impact of an HIV intervention when fitted to data from Bangalore. With the simple model, mixing scenarios with increased amounts of assortative (within-group) mixing tended to give rise to a higher R0 and increased the likelihood that an epidemic would occur. When the complex model was fit to HIV prevalence data, large differences in the level of assortative mixing were seen between the fits identified using different mixing scenarios, but little difference was projected in future HIV prevalence trends. An oral pre-exposure prophylaxis (PrEP) intervention was modelled, targeted at the different identity groups. For intervention strategies targeting the receptive or receptive and versatile MSM together, the overall impact was very similar for different mixing patterns. However, for PrEP scenarios targeting insertive or versatile MSM alone, the overall impact varied considerably for different mixing scenarios; more impact was achieved with greater levels of disassortative mixing.

From a series of zonal mean global stratospheric tracer measurements sampled in altitude vs. latitude, circulation and mixing patterns are inferred by the inverse solution of the continuity equation. As a first step, the continuity equation is written as a tendency equation, which is numerically integrated over time to predict a later atmospheric state, i.e., mixing ratio and air density. The integration is formally performed by the multiplication of the initially measured atmospheric state vector by a linear prediction operator. Further, the derivative of the predicted atmospheric state with respect to the wind vector components and mixing coefficients is used to find the most likely wind vector components and mixing coefficients which minimize the residual between the predicted atmospheric state and the later measurement of the atmospheric state. Unless multiple tracers are used, this inversion problem is under-determined, and dispersive behavior of the prediction further destabilizes the inversion. Both these problems are addressed by regularization. For this purpose, a first-order smoothness constraint has been chosen. The usefulness of this method is demonstrated by application to various tracer measurements recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). This method aims at a diagnosis of the Brewer–Dobson circulation without involving the concept of the mean age of stratospheric air, and related problems like the stratospheric tape recorder, or intrusions of mesospheric air into the stratosphere.

A comprehensive mathematical model is developed to simulate the ethylene polymerization in high-pressure autoclave reactors. Two generalised macromixing models, namely the external recycle and the backflow model are established to describe the complex mixing patterns occurring in multizone, multifeed low density polyethylene (LDPE) autoclaves. According to these models, each zone in the reactor is divided into a sequence of perfectly mixed vessels, called segments. To represent the kinetics of ethylene polymerization a general reaction mechanism is considered and the method of moments is employed to calculate the molecular weight developments. A new technique the so-called ‘numerical fractionation’ is applied to predict the formation of gel and the number chain length distribution in LDPE autoclaves. Finally, a detailed stability analysis is carried out for an LDPE autoclave to identify the number of multiple steady-states.

Assuming three generations of Majorana neutrinos, we study the different mixing patterns that arise from the non-trivial breaking of the flavor group A5 and CP to the residual symmetries Z3, Z5 or Z2 x Z2 in the charged lepton and to Z2 x CP in the neutrino sector. All patterns contain only one free parameter theta and thus mixing angles as well as the Dirac and the two Majorana phases are strongly correlated. We perform an analytical and a numerical study of all possible mixing patterns. It turns out that only four patterns can describe the experimentally measured values of the mixing angles for a particular choice of theta well. All of them predict trivial Majorana phases, while the Dirac phase delta is maximal for two patterns and trivial for the two remaining ones. If delta is maximal, also the atmospheric mixing angle is fixed to be maximal., Comment: 1+26 pages, 1 table, 2 figures; v2: matches version published in JHEP

Background Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used primarily in the critical care setting for patients concurrently supported by invasive or noninvasive positive pressure ventilation. NO delivery devices interface with ventilator breathing circuits to inject NO in proportion with the flow of air/oxygen through the circuit, in order to maintain a constant, target concentration of inhaled NO. Methods In the present article, a NO injection and mixing element is presented. The device borrows from the design of static elements to promote rapid mixing of injected NO-containing gas with breathing circuit gases. Bench experiments are reported to demonstrate the improved mixing afforded by the injection and mixing element, as compared with conventional breathing circuit adapters, for NO injection into breathing circuits. Computational fluid dynamics simulations are also presented to illustrate mixing patterns and nitrogen dioxide production within the element. Results Over the range of air flow rates and target NO concentrations investigated, mixing length, defined as the downstream distance required for NO concentration to reach within ±5 % of the target concentration, was as high as 47 cm for the conventional breathing circuit adapters, but did not exceed 7.8 cm for the injection and mixing element. Conclusion The injection and mixing element has potential to improve ease of use, compatibility and safety of inhaled NO administration with mechanical ventilators and gas delivery devices.

Background Mixing between sexual activity classes is an important determinant of sexually transmitted disease transmission. However, attempts to estimate sexual mixing patterns in the field remain limited partly because of practical and methodological difficulties. Goal To evaluate and identify appropriate sampling schemes to estimate the mixing pattern between sexual activity classes from large population networks with one or more components. Study design The study is based on simulations of large population networks with various structural characteristics. A variety of snowball sampling schemes are applied to these networks and are evaluated by the quality of the mixing matrix estimates that they produce. Results and conclusions Unbiased estimation of mixing patterns (global assortativity, within-group mixing of the lowest activity classes, within-group mixing of the highest activity classes) from large population networks is possible with a snowball sampling design in which the initial sample of index cases is drawn from the general population, all partners of the index case are recruited, and only one generation of partners are traced (one cycle). Simulation techniques proved useful in addressing complex methodological issues in situations where analytic results are difficult to obtain.

Tree species mixtures can overyield monospecific stands and provide many other advantageous regulating and provisioning ecosystem services. So far, the effect of mixing on growth were mostly described at the individual tree level or cumulatively at the stand level. How overyielding emerges from the mixing pattern, how it is modulated by the current environmental conditions, and how overyielding develops with progressing stand age is largely unexplored. However, such knowledge might promote the silvicultural design of mixed stands. Here, we use 50 long-term experimental plots in Germany with repeated spatially explicit stand inventories. They cover monospecific and mixed species stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.), sessile oak (Quercus petraea [Matt.] Liebl.) and European beech, and Scots pine (Pinus sylvestris L.) and European beech. The stands represent medium to very good site conditions, fully to moderately thinned 15–238 years-old stands with mixing patterns ranging from single-tree and group-mixture to monospecific stands. The main hypothesis is that mixing pattern, environmental conditions, and stand age modulate the stand growth and overyielding of mixed versus monospecific stands. Based on metrics of mixing the mixing pattern and indices of environmental conditions we show that mixed stands of European beech were on averaged by 12–36% more productive than respective monocultures. Overyielding can increase with stand density, mixing degree, regularity of horizontal tree distribution, tree size variation, site index, and water supply. Overyielding continued throughout the whole rotation time. The found overyielding suggests general facilitative effects of mixing in terms of bioclimate or soil conditions, independent of the mixing pattern. In addition to this general effect, overyielding was increased by stand density and mixing degree. This suggests a strong competition reduction due to structural complementarity. That the overyielding increases in moist years, points to the competition reduction as dominant cause. We hypothesize that in moist years competition for light and nutrient becomes stronger, so that species complementarity is more important and competition reduction may operate stronger and more beneficial for growth than in years with growth limitation by water. The findings stress the relevance of spatially explicit approaches of analyzing and modelling facilitation and competition at the stand and tree level. Silvicultural prescriptions may incorporate the findings that the analyzed mixtures with European beech in general overyield monospecific stands and that the benefit can be further increased by stand density, mixing degree, and tree size variation. Beneficial effects of mixtures can be expected on medium to high quality sites, in dry years, and even more in moist periods.