992 research outputs found
Total angular momentum representation for atom-molecule collisions in electric fields
It is shown that the atom-molecule collision problem in the presence of an
external electric field can be solved using the total angular momentum
representation in the body-fixed coordinated frame, leading to a
computationally efficient method for ab initio modeling of low-temperature
scattering phenomena. Our calculations demonstrate rapid convergence of the
cross sections for vibrational and Stark relaxation in He-CaD collisions with
the number of total angular momentum states in the basis set, leading to a
5-100 fold increase in computational efficiency over the previously used
methods based on the fully uncoupled space-fixed representation. These results
open up the possibility of carrying out numerically converged quantum
scattering calculations on a wide array of atom-molecule collisions and
chemical reactions in the presence of electric fields.Comment: 19 pages, 3 figures, 1 tabl
Compressible flow structures interaction with a two-dimensional ejector: a cold-flow study
An experimental study has been conducted to examine the interaction of compressible flow structures such as
shocks and vortices with a two-dimensional ejector geometry using a shock-tube facility. Three diaphragm pressure
ratios ofP4
=P1 = 4, 8, and 12 have been employed, whereP4
is the driver gas pressure andP1
is the pressure within
the driven compartment of the shock tube. These lead to incident shock Mach numbers of Ms = 1:34, 1.54, and 1.66,
respectively. The length of the driver section of the shock tube was 700 mm. Air was used for both the driver and
driven gases. High-speed shadowgraphy was employed to visualize the induced flowfield. Pressure measurements
were taken at different locations along the test section to study theflow quantitatively. The induced flow is unsteady
and dependent on the degree of compressibility of the initial shock wave generated by the rupture of the diaphragm
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Gas recognition based on the physicochemical parameters determined by monitoring diffusion rates in microfluidic channels
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Monitoring the diffusion progress rates of different gases in a microfluidic channel affords their
discrimination by the comparison of their temporal profiles in a high-dimensional feature space. Here, we
demonstrate gas recognition by determination of their three important physicochemical parameters via a
model-based examination of the experimentally determined diffusion rates in two different cross-section
channels. The system utilized comprises two channels with respective cross-sectional diameters of 1000 μm
and 50 μm. The open end of both channels are simultaneously exposed to the analyte, and the temporal
profiles of the diffusion rates are recorded by continuous resistance measurements on the chemoresistive
sensors spliced to the channels at their other ends. Fitting the solutions of the diffusion equation to the
experimental profiles obtained from the large cross-section channel results in the diffusivity of the analyte.
The results of small cross-section channel, however, fit the solutions of a modified diffusion equation which
accounts for the adsorption of the analyte molecules to the channel walls, as well. The latter fitting process
results in the adsorption parameter for the analyte-channel wall interactions and the population of the
effective adsorption sites on the unit area of the walls. The allocation of these three meaningful parameters to
an unknown gaseous analyte affords its recognition
Exciton coherence lifetimes from electronic structure
We model the coherent energy transfer of an electronic excitation within
covalently linked aromatic homodimers from first-principles, to answer whether
the usual models of the bath calculated via detailed electronic structure
calculations can reproduce the key dynamics. For these systems the timescales
of coherent transport are experimentally known from time-dependent polarization
anisotropy measurements, and so we can directly assess the whether current
techniques might be predictive for this phenomenon. Two choices of electronic
basis states are investigated, and their relative merits discussed regarding
the predictions of the perturbative model. The coupling of the electronic
degrees of freedom to the nuclear degrees of freedom is calculated rather than
assumed, and the fluorescence anisotropy decay is directly reproduced.
Surprisingly we find that although TDDFT absolute energies are routinely in
error by orders of magnitude more than the coupling energy, the coherent
transport properties of these dimers can be semi-quantitatively reproduced from
first-principles. The directions which must be pursued to yield predictive and
reliable prediction of coherent transport are suggested.Comment: 22 pages, 7 figure
Extension of the Morris-Shore transformation to multilevel ladders
We describe situations in which chains of N degenerate quantum energy levels,
coupled by time-dependent external fields, can be replaced by independent sets
of chains of length N, N-1,...,2 and sets of uncoupled single states. The
transformation is a generalization of the two-level Morris-Shore transformation
[J.R. Morris and B.W. Shore, Phys. Rev. A 27, 906 (1983)]. We illustrate the
procedure with examples of three-level chains
Nano-Fe3O4/O2: Green, Magnetic and Reusable Catalytic System for the Synthesis of Benzimidazoles
Magnetic nano-Fe3O4 was applied in the presence of atmospheric air as a green, efficient, heterogeneous and reusable catalytic system for the synthesis of benzimidazoles via the reactions of o-phenylenediamine (1 eq) with aryl aldehydes (1 eq) in excellentyields (85–97 %) and short reaction times (30–100 min) with a proposed mechanism.Keywords: Benzimidazole, benzene-1,2-diamine, aldehyde, nano-Fe3O4, heterogeneous catalyst, magnetite, O
Laser Induced Selective Alignment of Water Spin Isomers
We consider laser alignment of ortho and para spin isomers of water molecules
by using strong and short off-resonance laser pulses. A single pulse is found
to create a distinct transient alignment and antialignment of the isomeric
species. We suggest selective alignment of one isomeric species (leaving the
other species randomly aligned) by a pair of two laser pulses.Comment: 6 pages, 4 figures, 3 table
Sulfonic acid functionalized imidazolium salts/ FeCl3 as novel and highly efficient catalytic systems for the synthesis of benzimidazoles at room temperature
AbstractIonic liquid 3-methyl-1-sulfonic acid imidazolium chloride/ FeCl3, as well as ionic liquid 1, 3-disulfonic acid imidazolium chloride/ FeCl3 catalytic systems, efficiently catalyzes the condensation of benzene-1, 2-diamine with aromatic aldehydes in the presence of atmospheric air as a green oxidant in ethyl acetate at room temperature to afford benzimidazole derivatives in high yields and in short reaction times. The reaction is also efficiently performed when carboxylic acids are used instead of aldehydes
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