Equivariant Euler characteristics are important numerical homotopy invariants for objects with group actions. They have deep connections with many other areas like modular representation theory and ...chromatic homotopy theory. They are also computable, especially for combinatorial objects like partition posets, buildings associated with finite groups of Lie types, etc. In this article, we make new contributions to concrete computations by determining the equivariant Euler characteristics for all subgroup complexes of symmetric groups
Σ
n
when n is prime, twice a prime, or a power of two and several variants. There are two basic approaches to calculating equivariant Euler characteristics. One is based on a recursion formula and generating functions, and another on analyzing the fixed points of abelian subgroups. In this article, we adopt the second approach since the fixed points of abelian subgroups are simple in this case.
When acting in complex sociocultural contexts, designers often encounter other people engaged in differing practices. Non-design practices and design practices co-evolve in reciprocity. However, this ...study suggests that in design culture designers are too often encouraged to be uncritically reliant on performing established design activities as a crucial means of demonstrating their professionalism. Designers may encounter difficulties in concretely perceiving and describing how their everyday practices are entangled with people and things – a detached position which can prompt design professionals’ self-doubt about whether they contribute positively to others’ lives. This article explores how to aid designers in building attentiveness to the situated nature of their design practice. Drawing on recent practice theory, the possibility entails attending to the relational practices of others that occur in the proximity of an acting designer. Design and other practices become relational since these practices mutually constitute each other’s conditions of existence, maintenance, and transformation. Using autoethnography and analysis, the article reveals the positive potentials of four ways of attending to relational practices: tracking, recounting, repositioning, and responding. While non-exhaustive, these four categories can enable designers to develop a more nuanced understanding of their working context and appropriate localized strategies for design action.
•This article supports designers to act in a situation of plural-practice coexistence.•Detached perspectives may cause designers to question whether they make meaningful contributions to others.•Practices can form relations as they gather in proximity, shaping each other’s conditions of existence, maintenance, and transformation.•Attending to relational practices aids designers in developing localized action strategies and building nuanced understandings of context.•This article brings forward four ways to attend to relational practices through auto-ethnography.
This paper significantly extends previous studies to the transition regime by employing the second-order slip boundary conditions. A simple analytical model with second-order slip boundary conditions ...for a normalized Poiseuille number is proposed. The model can be applied to either rarefied gas flows or apparent liquid slip flows. The developed simple models can be used to predict the Poiseuille number, mass flow rate, tangential momentum accommodation coefficient, pressure distribution of gaseous flow in noncircular microchannels and nanochannels by the research community for the practical engineering design of microchannels and nanochannels. The developed second-order models are preferable since the difficulty and “investment” is negligible compared with the cost of alternative methods such as molecular simulations or solutions of Boltzmann equation. Navier–Stokes equations with second-order slip models can be used to predict quantities of engineering interest such as the Poiseuille number, tangential momentum accommodation coefficient, mass flow rate, pressure distribution, and pressure drop beyond its typically acknowledged limit of application. The appropriate or effective second-order slip coefficients include the contribution of the Knudsen layers in order to capture the complete solution of the Boltzmann equation for the Poiseuille number, mass flow rate, and pressure distribution. It could be reasonable that various researchers proposed different second-order slip coefficients because the values are naturally different in different Knudsen number regimes. It is analytically shown that the Knudsen’s minimum can be predicted with the second-order model and the Knudsen value of the occurrence of Knudsen’s minimum depends on inlet and outlet pressure ratio. The compressibility and rarefaction effects on mass flow rate and the curvature of the pressure distribution by employing first-order and second-order slip flow models are analyzed and compared. The condition of linear pressure distribution is given.
In lakes, suspended inorganic particles and dissolved substance are able to absorb or scatter different light wavelengths, leading to the changes of underwater light spectra which are highly related ...to the water quality. In turn, such changes could form environmental filtering for phytoplankton community to select particular algal populations via intensive competition for light resources. As an example, eutrophic lakes where underwater light spectra changed dramatically have a result of cyanobacterial blooms. In this study, in order to test the effect of light spectrum on growth and competition of green algae and cyanobacteria,
Chlorella pyrenoidosa
(a common green alga) and
Microcystis aeruginosa
(a bloom-forming cyanobacterium) grew and competed under three light colors: white (400–700 nm), red (620–700 nm), and blue (410–490 nm) light. Mono- and co-cultured systems were designed and population dynamics of the two species were monitored. The Lotka-Volterra model was used to quantify interspecific competition. Moreover, their photosynthetic activities were measured in mono-cultures. Results showed that in mono-cultures, red light was more favorable for
M. aeruginosa
, while blue light promoted the growth of
C. pyrenoidosa
. In co-cultures,
M. aeruginosa
won in red light and white light, while
C. pyrenoidosa
dominated under blue light. Light color mainly affected the absorption flux of reaction center (ABS/RC) in photosynthetic system II (PSII) and its potential photosynthetic capacity (
F
v
/
F
m
).
F
v
/
F
m
of
M. aeruginosa
in red light (or
C. pyrenoidosa
in blue light) was significantly enhanced. This study revealed that light color showed a significant influence on interspecific competition between green algae and cyanobacteria, which offers new insights into the dominance establishment and bloom formation of
Microcystis
.
A numerical investigation is conducted to study the heat transfer characteristics of laminar flow in three-dimensional rectangular microchannels with aspect ratios of 0.1–1 and Reynolds numbers of ...5–400. In this paper, the effects of aspect ratio and Reynolds number on the local and mean Nusselt numbers are presented in detail. Good agreement on Nusselt numbers is observed between the present results and the data reported in the literature. The results show that the Reynolds number has a great impact on the local Nusselt number in the thermally developing region, especially at lower Reynolds number, while the Reynolds number is independent of the developed Nusselt number. The local Nusselt number is found to increase with decreasing aspect ratio at the same Reynolds number. Additionally, the effects of these parameters on the dimensionless thermal entrance length are also investigated. The dimensionless thermal entrance length for rectangular microchannels monotonously increases by increasing aspect ratio and decreasing Reynolds number, whereas the effect of Reynolds number on the dimensionless thermal entrance length can be basically ignored when Reynolds number is more than 50. Generalized correlations are developed for the local Nusselt number and the dimensionless thermal entrance length.
The objective of this paper is to furnish the research and design communities with a simple and convenient means of predicting quantities of engineering interest for slip flow in doubly connected ...microchannels. Slip flow in doubly connected microchannels has been examined and a simple model is proposed to predict the friction factor and Reynolds number product. As doubly connected regions are inherently more difficult to solve than simply connected regions, and for slip flow no solutions or graphical and tabulated data exist for nearly all doubly connected geometries, the developed simple model fills this void and can be used to predict friction factor and Reynolds number product, mass flow rate, pressure distribution, and pressure drop of slip flow in doubly connected microchannels for the practical engineering design of doubly connected microchannels. The proposed models are preferable since the effects of various independent parameters are demonstrated and the difficulty and investment is completely negligible compared with the cost of alternative numerical methods.
► This paper provides a simple means of predicting quantities of engineering interest. ► The proposed models fill this void for slip flow in doubly connected microchannels. ► This paper demonstrates the effects of various independent parameters. ► The models are a weak function of the doubly connected duct shape. ► The models indicate trends expected from future numerical data and experiments.
Extracellular polysaccharide (EPS) can be distinguished into soluble or bound types and significantly contributes to colony formation in
Microcystis
. Depending on the binding strength with cells, ...the bilayer structure of bound EPS contains loosely or tightly bound EPS (LB-EPS or TB-EPS) and their roles in shaping the size and tightness of
Microcystis
colonies deserve further investigation. In this study, the influences of two types of bound EPS on the size and tightness of
Microcystis
colonies were investigated after a series of pretreatment to obtain LB-EPS retaining or stripped samples. Results showed that cells with LB-EPS formed large and loose colonies. Furthermore, the ratios of LB-EPS to TB-EPS, which indicate the size and tightness of the colonies, were higher in the retaining groups than in the stripped groups. Our findings also provide evidence that calcium enrichment is conducive to colony formation in
Microcystis
. This study provides new insights into the formation and enlargement of
Microcystis
colonies, which contributes to a better understanding on the role of EPS in
Microcystis
aggregation and morphology changes.
•Colony formation in two colonial Microcystis strains was investigated under a range of temperatures and nutrients (P and N) availability.•An increase in temperatures from 15 to 25 °C considerably ...promotes the colony size of Microcystis, whereas a significantly intraspecific variation is observed at a higher temperature (30 °C).•Higher phosphorus availability elevates the colony size of Microcystis but nitrogen has no significant influence.•A new index, adhesion ratio, is developed to quantify the adhesion effect on colony formation.•Adhesion effect significantly contributes to the formation of large colonies, but growth rate is a driving factor on the process.
The ability of Microcystis to form large colonies is a key trait that contributes to competition ability over other phytoplankton and facilitates the formation of surface scums in many freshwater systems. The effect of temperature and nutrients on this trait, however, is far from clear and needs further investigation, especially under a warmer climate and nutrient overloading in aquatic systems globally. In this study, two colonial strains of Microcystis (M. wesenbergii and M. ichthyoblabe) originally isolated from Lake Taihu in China, were used to investigate cyanobacterial aggregation under a range of temperatures (15–30 °C), phosphorus availability (0.004–8 mg P L−1), and nitrogen availability (0.04–40 mg N L−1). The mechanism of colony formation in Microcystis was determined based on growth rates and extracellular polysaccharide (EPS) contents. The colony size of both strains increased significantly when the temperature rose from 15 to 25 °C. A further increase in temperature from 25 to 30 °C, however, reduced the colony size of M. ichthyoblabe significantly, and, in contrast, increased the colony size of M. wesenbergii. Higher phosphorus availability promoted the formation of larger colonies in both strains. In comparison, nitrogen had no significant effect on the colony size. Furthermore, although EPS was a significant contributor to the formation of large colonies in colonial Microcystis, growth rate was a dominant driving factor in this process. The findings of this study highlight that warmer temperatures and phosphorus enrichment might enhance surface Microcystis scums directly through increasing the colony size. This study also provides new insights into the mechanism of colony formation in Microcystis.
Co-combustion characteristics and interactions of municipal solid waste (MSW) and low-rank coal semi-coke (LCSC) in O
2
/CO
2
or air atmosphere are investigated by the thermogravimetric method, ...including analyses of thermodynamic, kinetic parameters and reaction mechanism function. Results indicated that addition of MSW and higher oxygen concentration improve the co-combustion performance of blends. There are three distinct peaks for co-combustion of blends in air atmosphere, while only two peaks in 30O
2
/70CO
2
atmosphere. It indicates that the presence of CO
2
in oxy-fuel atmosphere is conducive to semi-char burnout. Interactions of MSW and LCSC mainly occur between 260 °C and 650 °C, and the synergetic interaction is very obvious around the second peak region of combustion process. The average activation energies
E
a
show an upward trend with the increase in oxygen concentration, and the minimum value of
E
a
is obtained when the blend ratio of MSW is 50% which might be an optimal option for co-combustion of blends. Activation energy, enthalpy changes, Gibbs function and entropy changes for 50MSW50LCSC in 30O
2
/70CO
2
atmosphere are 140.86 kJ mol
−1
, 138.33 kJ mol
−1
, 161.94 kJ mol
−1
and − 41.44 J mol
−1
K
−1
, respectively. In O
2
/CO
2
atmospheres, F6 and F1 functions are more suitable to describe the starting and subsequent process of entail reaction. The results can provide a theoretical and practical guidance for the harmless disposal and resource utilization of MSW and LCSC.
In composite structures or complex concrete members, some concrete bears multiple forces, called core concrete. The properties of the core concrete are variable under complex stress conditions, which ...will influence the structure performance analysis. Therefore, it is necessary to establish an accurate and theoretical constitutive model of concrete under complex stress conditions. The elastic–plastic properties of concrete in complex stress conditions were analyzed first. Then, the failure criterion of concrete in complex stress conditions was discussed to identify the key parameters. And the relationship between the stress–strain curve and failure criterion was analyzed through mathematical derivation. Finally, the multi-dimensional iterative constitutive model of concrete under complex stress conditions was established and verified. Based on the analysis results, the concrete under multi-axial stress conditions shows a spindle-shape stress envelope diagram. The failure criterion should be established by the analysis of concrete under high multi-axial compression conditions, tension–compression conditions, and shear–compression conditions. The plastic modulus is the key to reflecting the plastic strain development trend and the stress–strain relationship.
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