457 research outputs found
Molecular dynamics investigation of interfacial adhesion between oxidised bitumen and mineral surfaces
The interfacial adhesion between oxidised bitumen and mineral surfaces at dry and wet conditions was investigated using molecular dynamics (MD) simulations. Molecular models were built for virgin and oxidised bitumen components including saturate, aromatic, resin and asphaltenes. The bitumen models and four representative mineral substrates (namely quartz, calcite, albite and microcline) were employed to construct bitumen-mineral interface systems. These models were validated by the experimental results and MD simulations reported in the literature. The hardening mechanism of the aged bitumen was analysed by comparing the density, cohesive energy density and fraction of free volume between the virgin and oxidised bitumen. Work of adhesion was computed to quantify the adhesive bonding property of the bitumen-mineral interface systems for the virgin, lightly oxidised and heavily oxidised bitumen models under dry and wet conditions. Results show that the oxidised products (carbonyl and sulfoxide) strengthen the intermolecular bonding, resulting in molecular aggregation and physical hardening of the aged bitumen. When bitumen becomes oxidised at the dry condition, the interfacial adhesion of bitumen-acidic minerals (quartz) is dominated by van der Waals interaction which decreases due to the increased bitumen-quartz intermolecular distance caused by the aggregated bitumen molecules during aging. In comparison, the interfacial adhesion of bitumen-strong alkali minerals (albite and microcline) is dominated by electrostatic energy which increases due to higher polarity introduced by the oxidised products. For the bitumen-weak alkali mineral (calcite), the interfacial adhesion is attributed to both electrostatic energy and van der Waals energy, where compared to the virgin bitumen, the electrostatic energy becomes lower for the lightly-oxidised bitumen due to the increased bitumen-mineral distance but becomes higher for the heavily-oxidised bitumen due to higher polarity. At wet condition, water is the dominating factor that affects (weakens) the interfacial adhesion between the bitumen and the acidic minerals (quartz), and the oxidative aging of bitumen is the major factor that affects (strengthens) the interfacial adhesion between the bitumen and the strongly alkaline minerals (albite and microcline). For the weak alkali minerals such as calcite, both water and bitumen aging can significantly affect the interfacial adhesion
STGIC: a graph and image convolution-based method for spatial transcriptomic clustering
Spatial transcriptomic (ST) clustering employs spatial and transcription
information to group spots spatially coherent and transcriptionally similar
together into the same spatial domain. Graph convolution network (GCN) and
graph attention network (GAT), fed with spatial coordinates derived adjacency
and transcription profile derived feature matrix are often used to solve the
problem. Our proposed method STGIC (spatial transcriptomic clustering with
graph and image convolution) utilizes an adaptive graph convolution (AGC) to
get high quality pseudo-labels and then resorts to dilated convolution
framework (DCF) for virtual image converted from gene expression information
and spatial coordinates of spots. The dilation rates and kernel sizes are set
appropriately and updating of weight values in the kernels is made to be
subject to the spatial distance from the position of corresponding elements to
kernel centers so that feature extraction of each spot is better guided by
spatial distance to neighbor spots. Self-supervision realized by KL-divergence,
spatial continuity loss and cross entropy calculated among spots with high
confidence pseudo-labels make up the training objective of DCF. STGIC attains
state-of-the-art (SOTA) clustering performance on the benchmark dataset of
human dorsolateral prefrontal cortex (DLPFC). Besides, it's capable of
depicting fine structures of other tissues from other species as well as
guiding the identification of marker genes. Also, STGIC is expandable to
Stereo-seq data with high spatial resolution.Comment: Major revision has been made to generate the current version as
follows: 1. Writing style has been thoroughly changed. 2. Four more datasets
have been added. 3. Contrastive learning has been removed since it doesn't
make significant difference to the performance. 4. Two more authors are adde
Optimal coherent control of CARS: signal enhancement and background elimination
The ability to enhance resonant signals and eliminate the non-resonant
background is analyzed for Coherent Anti-Stokes Raman Scattering (CARS). The
analysis is done at a specific frequency as well as for broadband excitation
using femtosecond pulse-shaping techniques. An appropriate objective functional
is employed to balance resonant signal enhancement against non-resonant
background suppression. Optimal enhancement of the signal and minimization of
the background can be achieved by shaping the probe pulse alone while keeping
the pump and Stokes pulses in transform-limited-form (TLF). In some cases
analytical forms for the probe pulse can be found, and numerical simulations
are carried out for other circumstances. It is found that a good approximate
solution for the optimal pulse in the two-pulse CARS is a superposition of
linear and arctangent type phases for the pump. The well-known probe delay
method is shown to be a quasi-optimal scheme for background suppression. The
results should provide a basis to improve the performance of CARS spectroscopy
and microscopy.Comment: 11 pages,10 figures, JC
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