Mixing in a microfluidic system is challenging due to dominant diffusion effects at a microscale (low Reynolds number). In this work, we report the improvement of mixing performance in spiral ...microchannels of varying cross-sectional geometry and hydraulic diameter. The formation of secondary flow interactions in spiral channels, known as Dean vortices, aid the primary diffusion process. The evolution of these Dean vortices was experimentally visualized along the length of the microchannel by confocal microscopy, and then compared to numerical studies. The cross-sectional geometries of the spiral channels, especially in the case of irregular shapes such as the semi-circular and trapezoidal profiles, were found to be an important factor in tuning the strength of Dean vortices, which in turn dictate the mixing performance, as opposed to diffusion which is more prominent at lower Re. This experiment-based finding has been validated via the evaluation of swirling strength of the working fluid, obtained using a numerical study. The results thus obtained show a mixing performance greater than 90% above a Reynolds number of 20 for most spiral channel designs, making this system suitable for high throughput operation with reduced pressure drop. This work is the first to experimentally and numerically demonstrate, within this operating range (20 < Re < 277), the impact on mixing performance in curved microchannels of varying cross-sectional geometries of constant cross-sectional area, and of varying hydraulic diameters for square shaped channels. The capability of these channels to operate at a moderately high Re with enhanced mixing performance and reduced pressure drop would be of great use in large-scale industrial operations, such as complex integrated micro-reactors wherein pressure drop plays a key role.
The rovibrational spectra of freely rotating gas phase molecules are often plagued by spectral congestion due to the high density of rotational peaks. The congestion is especially severe at higher ...infrared frequencies due to the large numbers of overlapping overtones and combination bands that form polyads. As a result, rovibrational peaks in the near-infrared region of the spectrum are seldom assigned. This work describes how two-dimensional (2D) rovibrational spectroscopy can use the coupling between vibrational modes to isolate rovibrational bands that would otherwise remain overlapped and congested. Multidimensional spectroscopic techniques that make use of the large number of cross-peaks that form rich 2D rovibrational patterns are explored. Propyne is used to demonstrate 2D methods for identifying the frequencies and symmetries of coupled vibrations and for assigning rotational quantum numbers, even in regions that are heavily congested.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
London dispersion constitutes one of the fundamental interaction forces between atoms and between molecules. While modern computational methods have been developed to describe the strength of ...dispersive interactions in the gas phase properly, the importance of inter- and intramolecular dispersion in solution remains yet to be fully understood because experimental data are still sparse in that regard. We herein report a detailed experimental and computational study of the contribution of London dispersion to the bond dissociation of proton-bound dimers, both in the gas phase and in dichloromethane solution, showing that attenuation of inter- and intramolecular dispersive interaction by solvent is large (about 70% in dichloromethane), but not complete, and that current state-of-the-art implicit solvent models employed in quantum-mechanical computational studies treat London dispersion poorly, at least for this model system.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich cis-1,2-dimethoxycyclopropane. Upon Collision Induced Dissociation (CID), several ...spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M(+) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and the second to the methoxymethylidene metal complex IMes-M-HCOCH3(+). The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxymethylidene moiety as observed by the predominance of the bare cation IMes-M(+) channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxypropylene isomer before dissociation. However, for the abstraction of the methoxymethylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal-carbene bond strength.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
In this paper, we analyze the properties of effective coverage of the two-node team. Radial attenuation disk model is adopted for the individual model of coverage which conforms to the natural ...characteristics of devices in the real world. For any point in coverage overlapping regions of multiple nodes, based on the superposition principle, its coverage intensity equals the sum of individual coverage intensities, which complies with the collaboration behavior of output (influence) coverage applications. General properties of team’s effective coverage, including its region connectedness, and how it is related to the separation between the two nodes are first studied, followed by numerical analysis and simulations on the relations between nodes optimal separation and three different types of models.
Full text
Available for:
EMUNI, FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Calculable results: Complex density functional calculations and spin distribution analyses have been performed for planar and saddled iron(III) porphyrin complexes (see picture). The spin populations ...and the extent of the interactions between the metal and the porphyrin orbitals were determined, which can explain the large change of meso‐carbon atom chemical shifts observed for different porphyrin ligands.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The intramolecular magnetic interactions in one-electron oxidized iron(
iii
) porphyrin π-radical cations, Fe(OETPP&z.rad;)ClSbCl
6
(
1
), Fe(OMTPP&z.rad;)ClSbCl
6
(
2
) and Fe(TPP&z.rad;)ClSbCl
6
...(
3
), have been compared by means of X-ray crystallography, SQUID magnetometry, cyclic voltammetry, UV-Vis spectroelectrochemical analysis, NMR spectroscopy analysis and unrestricted DFT calculations. Unlike a generally recognized antiferromagnetic coupling d
xy
↑
d
xz
↑
d
yz
↑
d
z
2
↑
d
x
2
−
y
2
↑
P&z.rad;
+
(a
2u
)
↓
(
S
= 2) state
via
a weak bonding interaction as in (
3
), we have disclosed that a strong bonding interaction among iron d
x
2
−
y
2
and porphyrin a
2u
orbitals forms in (
1
) into a highly delocalized Ψ
π
= P&z.rad;
+
(a
2u
) + Fe
III
(d
x
2
−
y
2
, d
z
2
) orbital that is able to accommodate two spin-paired electrons to form the Ψ
π
2
d
xy
1
d
xz
1
d
yz
1
, d
z
2
1
(
S
= 2) ground state. Concurrently, the spin polarization effect is exerted on the paired spins in the Ψ
π
orbital by magnetic induction from the remaining unpaired electrons in the iron d orbitals. The interpretation mentioned above is further verified by the diamagnetic nature of the saddled copper(
ii
) porphyrin π-cation radical, Cu
II
(OETPP&z.rad;)(ClO
4
) (
S
= 0), where the strong bonding interaction leads to the Ψ
π
2
d
xy
2
d
xz
2
d
yz
2
d
z
2
2
(
S
= 0) ground state but no spin polarization exists. Thus, the magnetic nature of the iron(
iii
) porphyrin π-radical cation is tuneable by saddling the ring planarity.
The intramolecular magnetic interactions in one-electron oxidized iron(
iii
) porphyrin π-radical cations with planar and saddle conformations have been compared by means of a variety of spectroscopic, physical methods and unrestricted DFT calculations.
The rapid emergency of data science, information technology, and artificial intelligence (AI) relies on massive data processing with high computing efficiency and low power consumption. However, the ...current von‐Neumann architecture system requires high‐energy budget to process data computing and storage between central computing unit and memory. To overcome this problem, neuromorphic computing system which mimics the operation of human brain has been proposed to perform computing in an energy‐efficient manner. Recently, organic–inorganic halide perovskite compounds have been demonstrated as promising components for neuromorphic devices owing to their strong light absorption, solution processability, and unique properties such as ion migration, carrier trapping effects and phase transition. In this review paper, we report recent advances of neuromorphic devices which employed organic–inorganic halide perovskite compounds by analyzing their fundamental operating mechanisms, device architectures, applications and future prospective.
Neuromorphic devices have been attracted much attention as next generation computing system to process the large amount of data. This review paper reports on neuromorphic devices based on organic–inorganic halide perovskite compounds including fundamental operating mechanisms, device architectures, applications, and future prospective.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) over 25%. Though their high PCE can be achieved by optimizing absorber layer and device interfaces, the ...intrinsic instability of perovskite materials is still a key issue to be resolved. Mixed‐halide perovskites using multiple halogen constituents have been proved to improve robustness; however, the anion at the X site in the ABX3 formula is not limited to halogens. Other negative monovalent ions with similar properties to halogens, such as pseudo‐halogens, have the opportunity to form perovskites with ABX3 stoichiometry. Recently, thiocyanates and formates have been utilized to synthesize stable perovskite materials. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The intrinsic properties, their effects on crystal structure, and bandgap engineering of the pseudo‐halide perovskites are summarized. Various thiocyanate compounds applied in the fabrication of perovskite solar cells are discussed. The fabrication process, film formation mechanism, and crystallinity of pseudo‐halide perovskites are elucidated to understand their effects on the photovoltaic performance and device stability. Other applications of pseudo‐halide perovskites are summarized in the final section. Lastly, this review concludes with suggestions and outlooks for further research directions.
Monovalent pseudo‐halide anions share similar properties to halide anions. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The role of pseudo‐halides and their position and occupation in perovskite crystal, its impact on perovskite film quality, solar cell stability and photovoltaic performance, and pseudo‐halide optoelectronic devices beyond solar cells are compared comprehensively.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
