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result(s) for
"Critical mass"
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Women Directors on Corporate Boards: From Tokenism to Critical Mass
Academic debate on the strategic importance of women corporate directors is widely recognized and still open. However, most corporate boards have only one woman director or a small minority of women directors. Therefore they can still be considered as tokens. This article addresses the following question: does an increased number of women corporate boards result in a build up of critical mass that substantially contributes to firm innovation? The aim is to test if 'at least three women' could constitute the desired critical mass by identifying different minorities of women directors (one woman, two women and at least three women). Tests are conducted on a sample of 317 Norwegian firms. The results suggest that attaining critical mass - going from one or two women (a few tokens) to at least three women (consistent minority) - makes it possible to enhance the level of firm innovation. Moreover, the results show that the relationship between the critical mass of women directors and the level of firm innovation is mediated by board strategic tasks. Implications for both theory and practice, and future research directions are discussed.
Journal Article
Numerical Study on Pilot Ignition of a Thermally-Thick Solid Fuel with Low-Velocity Airflow in Microgravity
The mechanisms controlling the dependence on low-velocity flow of the piloted ignition of a solid material under external radiant heating is investigated through a numerical modeling. The poly (methyl methacrylate) (PMMA) was used as the fuel. The objective of the present study is to gain insight into the intrinsic ignition mechanisms of a solid fuel, as well as to gain a more comprehensive understanding of the dynamical characteristics of the ignition process near the extinction limit. For this purpose, a two-dimensional numerical model has been developed using the Fire Dynamic Simulator (FDS5) code, in which both solid-phase and gas-phase reactions are calculated. Two radiant heat flux, which are 16 and 25 kW/m2 were studied, and an external air flow was varied from 3 to 40 cm/s. The simulation results showed that transient gas reaction flashed before a continuous flame was attached to the sample surface for gas flow velocities lower than a critical value. As the flow velocity is reduced, the flashing time, which is defined as the time when any flame is seen above the sample surface, decreases, while the duration of flashing increases. The solid surface temperature and mass flow rate increase rapidly during flashing. The ignition time, which is defined as the time when a continuous flame is attached to the fuel surface, decreases, reaches a minimum, and then increases until ignition cannot occur. Mechanisms were considered to explain the ‘‘V-shaped” dependence of ignition time on flow-velocity, and two regimes were identified each having a different controlling mechanism: the mass transport regime where the ignition delay is controlled by the mixing of oxygen and pyrolyzate; and the heat transfer regime where the ignition delay is controlled by changes in convection heat losses and critical mass flux for ignition. With the decrease of the airflow velocity, the critical mass flux shows a trend of decreasing and then increasing, which is dominated by the mixing of the pyrolyzate and the oxidizer, while the critical temperature monotonically decreases, which is dominated by a reduction of the net heat flux at the fuel surface. The results provide further insight into the ignition behavior of solid fuel under low-velocity flow environment, and guidance about fire safety in microgravity environments.
Journal Article
A Comprehensive Experimental Investigation of Additives to Enhance Pool Boiling Heat Transfer of a Non-Azeotropic Mixture
Adding nanoparticles or surfactants to pure working fluid is a common and effective method to improve the heat transfer performance of pool boiling. The objective of this research is to determine whether additives have the same efficient impact on heat transfer enhancement of the non-azeotropic mixture. In this paper, Ethylene Glycol/Deionized Water (EG/DW) was selected as the representing non-azeotropic mixture, and a comparative experiment was carried out between it and the pure working fluid. In addition, the effects of different concentrations of additives on the pool boiling heat transfer performance under different heat fluxes were experimentally studied, including TiO2 nanoparticles with different particle diameters, different kinds of surfactants, and mixtures of nanofluids and surfactants. The experimental results showed that the nanoparticles deteriorated the heat transfer of the EG/DW solution, while the surfactant enhanced the heat transfer of the solution when the concentration closed to a critical mass fraction (CMC). However, the improvement effect was unsteady with the increase in the heat flux density. The experimental results suggest that the mass transfer resistance of the non-azeotropic mixture is the most important factor in affecting heat transfer enhancement. Solutions with 20 nm TiO2 obtained a steady optimum heat transfer improvement by adding surfactants.
Journal Article
On Global Solutions and Blow-Up for a Short-Ranged Chemical Signaling Loop
This paper aims at providing a substantial step toward the global boundedness and blow-up of solutions to a two-species and two-stimuli chemotaxis model, in which the process of the species results in a short-ranged chemical signaling loop. More precisely, we consider the following Neumann initial-boundary value problem
u
t
=
Δ
u
-
χ
1
∇
·
(
u
∇
v
)
,
x
∈
Ω
,
t
>
0
,
0
=
Δ
v
-
μ
2
+
w
,
x
∈
Ω
,
t
>
0
,
w
t
=
Δ
w
-
χ
2
∇
·
(
w
∇
z
)
-
χ
3
∇
·
(
w
∇
v
)
,
x
∈
Ω
,
t
>
0
,
0
=
Δ
z
-
μ
1
+
u
,
x
∈
Ω
,
t
>
0
in the unit disk
Ω
:
=
B
1
(
0
)
⊂
R
2
with chemotactic sensitivities
χ
1
>
0
,
χ
2
>
0
and
χ
3
≥
0
and radially symmetric nonnegative initial data
u
0
and
w
0
, where
μ
1
a
n
d
μ
2
are given, respectively, by
μ
1
:
=
m
1
|
Ω
|
and
μ
2
:
=
m
2
|
Ω
|
with
m
1
=
∫
Ω
u
0
,
m
2
=
∫
Ω
w
0
.
Explicit conditions on
χ
i
,
μ
i
,
u
0
and
w
0
are given for the simultaneous global boundedness and simultaneous finite-time blow-up of classical solutions. Specifically, when the effect of
χ
3
>
0
is strong enough in the sense that the dynamical properties of the above system behave like one single-species Keller–Segel chemotaxis system, it is shown that if only the total mass
m
2
<
4
π
χ
1
and
m
2
<
4
π
χ
3
, the solutions are globally bounded, while blow-up may occur provided that
m
2
>
4
π
χ
1
and
m
2
>
8
π
χ
3
. Moreover, in view of the chemotactic signaling loop, one can find a critical mass phenomenon:
if
2
m
1
+
m
2
χ
3
χ
2
<
8
π
χ
2
, the problem possesses only globally bounded solutions, whereas
if
8
π
m
1
χ
1
+
8
π
m
2
χ
2
<
2
m
1
m
2
+
m
2
2
χ
3
χ
2
and
∫
Ω
u
0
|
x
|
2
and
∫
Ω
w
0
|
x
|
2
are sufficiently small, the corresponding solution blows up in finite time in the sense that
lim sup
t
↗
T
|
|
u
(
·
,
t
)
|
|
L
∞
(
Ω
)
+
|
|
w
(
·
,
t
)
|
|
L
∞
(
Ω
)
→
∞
with some finite time
T
>
0
. The simultaneous blow-up phenomenon for two species is also given in this paper.
This, in particular, shows, when
χ
3
=
0
, that smallness of mass of each species implies global solvability, whereas largeness of masses induces blow-up to occur.
Journal Article
Climate Change Mitigation and the Collective Action Problem: Exploring Country Differences in Greenhouse Gas Contributions
Global climate change has become the collective action problem of our era. With the United Nations Framework Convention on Climate Change (UNFCCC) 2015 COP21 Meetings in Paris as the context, the author draws upon critical mass theory (CMT) (Oliver and Marwell 1988; Oliver, Marwell, and Teixeria 1985) in an attempt to yield greater understanding of the international community's ability to achieve climate stability as a global public good. Using CMT key elements of collective action production functions, group heterogeneity, and interdependence, the author explores the world's collective ability to mitigate greenhouse gas (GHG) emissions at the country level. Brief examples from Belize, Central America, and other small, vulnerable nations are used to focus attention on those countries that cannot make meaningful contribution to the collection action. The findings help illustrate why climate change is such a difficult collective action problem to address, what broad strategies might be required, and how to potentially achieve more targeted distribution of international resources.
Journal Article