Silica nanoparticles without any surface modification are not surface active at the toluene−water interface due to their extreme hydrophilicity but can be surface activated in situ by adsorbing ...cationic surfactant from water. This work investigates the effects of the molecular structure of water-soluble cationic surfactant on the surface activation of the nanoparticles by emulsion characterization, adsorption and zeta potential measurements, dispersion stability experiments, and determination of relevant contact angles. The results show that an adsorbed cationic surfactant monolayer on particle surfaces is responsible for the wettability modification of the particles. In the presence of a trace amount of cationic surfactant, the hydrophobicity of the particles increases, leading to the formation of stable oil-in-water O/W(1) emulsions. At high surfactant concentration (>cmc) the particle surface is retransformed to hydrophilic due to double-layer or hemimicelle formation, and the concentration of the free surfactant in the aqueous phase is high enough to stabilize emulsions alone. O/W(2) emulsions, probably costabilized by free surfactant and particles, are then formed. The monolayer adsorption seems to be charge-site dependent. Thus, using single-chain trimethylammonium bromide surfactants or a double-head gemini cationic surfactant, the hydrophobicity of the particles achieved is not sufficient to stabilize water-in-oil (W/O) emulsions, and no phase inversion is induced. However, using a double-chain cationic surfactant, the chain density on the particle surfaces endows them with a hydrophobicity high enough to stabilize W/O emulsions, and double phase inversion, O/W(1) → W/O → O/W(2), can then be achieved by increasing the surfactant concentration.
The in situ surface activation of unmodified CaCO3 nanoparticles by interaction with surfactant in aqueous media has been studied, and the impact of this on the foamability and foam stability of ...aqueous dispersions was assessed. Using complementary experiments including measurement of particle zeta potentials, adsorption isotherms of surfactant, air−water surface tensions, and relevant contact angles, the mechanism of this activation was revealed. The results show that the non-surface-active CaCO3 nanoparticles cannot be surface activated by interaction with cationic or nonionic surfactants but can be surface activated by interaction with anionic surfactants such as SDS and AOT, leading to a synergistic effect in both foamability and foam stability. The electrostatic interaction between the positive charges on particle surfaces and the negative charges of anionic surfactant headgroups results in monolayer adsorption of the surfactant at the particle−water interface and transforms the particles from hydrophilic to partially hydrophobic such that particles become surface active and stabilize bubbles. SDS is a more efficient surfactant for this surface activation than AOT. Possible reasons for this difference are suggested.
Kaon and pion parton distributions Cui, Z.-F.; Ding, M.; Gao, F. ...
The European physical journal. C, Particles and fields,
11/2020, Letnik:
80, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Beginning with results for the leading-twist two-particle distribution amplitudes of
π
- and
K
-mesons, each of which exhibits dilation driven by the mechanism responsible for the emergence of ...hadronic mass, we develop parameter-free predictions for the pointwise behaviour of all
π
and
K
distribution functions (DFs), including glue and sea. The large-
x
behaviour of each DF meets expectations based on quantum chromodynamics; the valence-quark distributions match extractions from available data, including the pion case when threshold resummation effects are included; and at
ζ
5
=
5.2
GeV, the scale of existing measurements, the light-front momentum of these hadrons is shared as follows:
⟨
x
valence
⟩
π
=
0.41
(
4
)
,
⟨
x
glue
⟩
π
=
0.45
(
2
)
,
⟨
x
sea
⟩
π
=
0.14
(
2
)
; and
⟨
x
valence
⟩
K
=
0.42
(
3
)
,
⟨
x
glue
⟩
K
=
0.44
(
2
)
,
⟨
x
sea
⟩
K
=
0.14
(
2
)
. The kaon’s glue and sea distributions are similar to those in the pion, although the inclusion of mass-dependent splitting functions introduces some differences on the valence-quark domain. This study should stimulate improved analyses of existing data and motivate new experiments sensitive to all
π
and
K
DFs. With little known empirically about the structure of the Standard Model’s (pseudo-) Nambu-Goldstone modes and analyses of existing, limited data being controversial, it is likely that new generation experiments at upgraded and anticipated facilities will provide the information needed to resolve the puzzles and complete the picture of these complex bound states.
We consider the fidelity of the vector meson dominance (VMD) assumption as an instrument for relating the electromagnetic vector-meson production reaction
e
+
p
→
e
′
+
V
+
p
to the purely hadronic ...process
V
+
p
→
V
+
p
. Analyses of the photon vacuum polarisation and the photon-quark vertex reveal that such a VMD
Ansatz
might be reasonable for light vector-mesons. However, when the vector-mesons are described by momentum-dependent bound-state amplitudes, VMD fails for heavy vector-mesons: it cannot be used reliably to estimate either a photon-to-vector-meson transition strength or the momentum dependence of those integrands that would arise in calculations of the different reaction amplitudes. Consequently, for processes involving heavy mesons, the veracity of both cross-section estimates and conclusions based on the VMD assumption should be reviewed, e.g., those relating to hidden-charm pentaquark production and the origin of the proton mass.
The effect of applied stress on the crevice corrosion of 304 stainless steel in 3.5 wt% solution is investigated. The delayed and immediate crevice corrosion of 304 stainless steel could occur under ...various applied stresses and different polarized potential. Both these two types of crevice corrosion are developed from the evolution of metastable pits. The lifetime of metastable pits is prolonged with the increased stress and the secondary metastable pit is observed under 400 MPa applied stress. This contributes to increased probability of metastable pits transiting to stable pits and then promotes crevice corrosion development with the increased stress.
•Crevice corrosion of 304 stainless steel is developed from metastable pits.•The concentration of defects in passive film increases with the increased stress.•The applied stress could drastically extend the lifetime of metastable pits.•Secondary metastable pit can be induced by applied plastic stress.•Array reference electrodes can monitor evolution of metastable pit inside crevice.
A symmetry-preserving approach to the two valence-body continuum bound-state problem is used to calculate the elastic electromagnetic form factors of the ρ-meson and subsequently to study the ...evolution of vector-meson form factors with current-quark mass. To facilitate a range of additional comparisons, K* form factors are also computed. The analysis reveals that vector mesons are larger than pseudoscalar mesons; composite vector mesons are nonspherical, with magnetic and quadrupole moments that deviate ∼30% from point-particle values; in many ways, vector-meson properties are as much influenced by emergent mass as those of pseudoscalars; and vector-meson electric form factors possess a zero at spacelike momentum transfer. Qualitative similarities between the electric form factors of the ρ and the proton, GEp, are used to argue that the character of emergent mass in the Standard Model can force a zero in GEp. Moreover, the existence of a zero in vector-meson electric form factors entails that a single-pole vector-meson dominance model can only be of limited use in estimating properties of off-shell vector mesons, providing poor guidance for systems in which the Higgs mechanism of mass generation is dominant.
Exploiting crossing symmetry, the hadron scale pion valence quark distribution function is used to predict the kindred elementary valence quark fragmentation function (FF). This function defines the ...kernel of a quark jet fragmentation equation, which is solved to obtain the full pion FFs. After evolution to a scale typical of FF fits to data, the results for quark FFs are seen to compare favourably with such fits. However, the gluon FF is markedly different. Notably, although FF evolution equations do not themselves guarantee momentum conservation, inclusion of a gluon FF which, for four quark flavours, distributes roughly 11% of the total light-front momentum fraction, is sufficient to restore momentum conservation under evolution. Overall, significant uncertainty is attached to FFs determined via fits to data; hence, the features of the predictions described herein could potentially provide useful guidance for future such studies.
In the present study, a consortium of two rhizobacteria Bacillus amyloliquefaciens Bk7 and Brevibacillus laterosporus B4, termed 'BB', biochemical elicitors salicylic acid and β-aminobutyric acid ...(SB) and their mixture (BBSB) were investigated for cold and drought stress tolerance in rice plants. After withholding water for 16 days, rice plants treated with BBSB showed 100% survival, improved seedling height (35.4 cm), shoot number (6.12), and showed minimum symptoms of chlorosis (19%), wilting (4%), necrosis (6%) and rolling of leaves. Similarly, BB inoculation enhanced plant growth and reduced overall symptoms in rice seedlings subjected to 0 ± 5 °C for 24 h. Our results imply several mechanisms underlying BB- and BBSB-elicited stress tolerance. In contrast to the control, both treatments significantly decreased leaf monodehydroascorbate (MDA) content and electrolyte leakage, and increased leaf proline and cholorophyll content. Moreover, activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) increased 3.0- and 3.6-fold, respectively. Moreover, expression of OsMYB3R-2, OsDIL, OsDREB1A and OsCDPK13 genes was significantly up-regulated, suggesting that these genes play important roles in abiotic stress tolerance of rice. In addition, bacterial strains Bk7 and B4 were able to produce high amounts of IAA and siderophores, and colonise the plant roots, while only strain Bk7 exhibited the capability to form biofilms and solubilise inorganic phosphate. This study indicates that the BB and BBSB bio-formulations can be used to confer induced systematic tolerance and improve the health of rice plants subject to chilling and drought stress.
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