Numerical test of scale relations for modelling coastal sandbar migration and inspiration to physical model design

Physical model experiments on sandbar migration are widely conducted in the wave flume to reveal its hydro-sediment dynamic mechanisms.Selecting an appropriate scale relation is an important part of designing a laboratory experiment.However,evaluating the scale effect is complicated since it is impractical to design wave flume experiments based on strict geometry scales derived from the prototype beach or other laboratory beaches.Here,a process-based numerical model is used to test the Dean and Shields similitudes by comparing sandbar migration and sediment transport in different undistorted model scales using natural sediments.The numerical model provides excellent predictions for both offshore sandbar migration on a real-world beach and onshore sandbar migration in the wave flume.Consistent with previous studies,sandbar offshore migration and suspended sediment transport are similar when the Dean similitude is fulfilled.Sandbar onshore migration and bedload transport can be well reproduced only if the Shields similitude is achieved.Although previous laboratory experiments of sandbar migration generally used the Dean similitude,it is found that the Shields similitude is effective and indispensable for modelling sandbar onshore migration,which will be underestimated if the Dean similitude is only considered.Each scale relation cannot be used simultaneously for modelling both onshore and offshore sandbar migration in physical models.

Study on dynamics of shear waves-Ⅰ. Scale analysis and dispersion relation

- Starting from satellite remote sensing data, the dynamical processes of shear waves occurring at the boundary between the western boundary current and the shelf slope water are studied and dynamically analyzed in this study. The average wavelength is 75 km, and the average amplitude (from crest to trough )17 km. the average phase speed 100 cms-1 for the shear waves along the north wall of the Gulf Stream to the east of Cape Hatteras measured from NOAA satellite IR (infrared ) images. The average wavelength of shear waves along the north wall of the Kuroshio Current is 57 km, and the average amplitude 17 km. For the shear waves occurring along the west wall of the Gulf Stream to the south of Cape Hatteras, the average wavelength is 131 km, and the average amplitude 33 km measured from Seasat SAR (synthetic aperture radar )images. The time for one cycle of shear wave event is about one week.In order to explore the dynamical mechanisms of shear waves, we solved the vorticity equation for a stratified fluid, and obtained an analytical expression of dispersion relation of shear waves. The results indicated that there was a parabolic relation between the phase speed and the wavelength of shear waves, and the mean flow field was an important factor in the dispersion relation. The latter point means that the horizontal tangent variation of velocity is a basic condition for shear wave occurrence. Theoretical analyses are confirmed by satellite remote sensing data.

Atomic Dispersed Hetero‑Pairs for Enhanced Electrocatalytic CO_(2)Reduction

Electrochemical carbon dioxide reduction reaction(CO_(2)RR)involves a variety of intermediates with highly correlated reaction and ad-desorption energies,hindering optimization of the catalytic activity.For example,increasing the binding of the*COOH to the active site will generally increase the*CO desorption energy.Breaking this relationship may be expected to dramatically improve the intrinsic activity of CO_(2)RR,but remains an unsolved challenge.Herein,we addressed this conundrum by constructing a unique atomic dispersed hetero-pair consisting of Mo-Fe di-atoms anchored on N-doped carbon carrier.This system shows an unprecedented CO_(2)RR intrinsic activity with TOF of 3336 h−1,high selectivity toward CO production,Faradaic efficiency of 95.96%at−0.60 V and excellent stability.Theoretical calculations show that the Mo-Fe diatomic sites increased the*COOH intermediate adsorption energy by bridging adsorption of*COOH intermediates.At the same time,d-d orbital coupling in the Mo-Fe di-atom results in electron delocalization and facilitates desorption of*CO intermediates.Thus,the undesirable correlation between these steps is broken.This work provides a promising approach,specifically the use of di-atoms,for breaking unfavorable relationships based on understanding of the catalytic mechanisms at the atomic scale.

Rational design of heterogeneous catalysts by breaking and rebuilding scaling relations

Various scaling relations have long been established in the field of heterogeneous catalysis,but the resultant volcano curves inherently limit the catalytic performance of catalyst candidates.On the other hand,it is still very challenging to develop universal descriptors that can be used in various types of catalysts and reaction systems.For these reasons,several strategies have recently been proposed to break and rebuild scaling relations to go beyond the top of volcanoes.In this review,some previously proposed descriptors have been briefly introduced.Then,the strategies for breaking known and establishing new and more generalized scaling relations in complex catalytic systems have been summarized.Finally,the application of machine-learning techniques in identifying universal descriptors for future computational design and high-throughput screening of heterogeneous catalysts has been discussed.

Dual metal atom catalysts:Advantages in electrocatalytic reactions

The dual-metal-atom catalysts(DACs)have aroused much attention as they possess the advantages of single-atom and metal alloy catalysts.And the DACs have exhibited enhanced performance in various electrocatalytic reactions,such as hydrogen/oxygen evolution and oxygen/carbon dioxide/nitrogen reduction.In this review,we mainly overview the latest understanding of the advantages of DACs for these reactions.This review will start with the familiar characterization methods for DACs,then the primary synthesis strategies for DACs will be discussed.Emphasis is given to the advantages of DACs in catalytic reactions,including the adsorption and activation,electronic structure regulation,breaking scaling relations,reducing energy barriers,cascading and coupling,synergy effect,and providing mechanism research platforms.Finally,personal perspectives and challenges for the further development of DACs are briefly discussed.

ON THE KINETICS AND MECHANISM OF THE COPOLYMERIZATION OF ACRYLONITRILE WITH STYRENE IN THE PRESENCE OF COPPER CHLORIDE

The copolymerization of styrene (St) and acrylonitrile (AN) complexed with CuCl_2 monomer by a free radicalmechanism was performed using benzoyl peroxide as an initiator at 65℃ under N_2 atmosphere for 150 min. The rate ofpolymerization (R_p) was found to increase linearly with the concentration (in mol/L) of CuCl_2, AN and St through scalingrelations. The activation energy of the copolymerization process in the presence and absence of CuCl_2 was found to be46.5 kJ/mol and 102 kJ/mol, respectively. The viscosity average molecular weigh of the copolymer and the k_p^2/k_t ratio weredctermired to further assess the accelerating effect of CuCl_2 on the copolymerization process. The copolymerization processin the presence of CuCl_2 has a radical complex mechanism.

Insights into electrochemical CO_2 reduction on tin oxides from first-principles calculations

Density functional theory calculations were used to unravel the mechanism of CO_2 electroreduction on SnO_x surfaces. Under highly reducing conditions(<-0.6 V vs. RHE), the SnO(101) surface with oxygen vacancies is likely the active phase for CO_2 reduction. We showed that the proton-electron transfer to adsorbed *CO_2 forming *OCHO, a key intermediate for producing HCOOH, is energetically more favorable than the formation of *COOH, justifying the selectivity trends observed on Sn-based electrocatalysts. With linear scaling relations, we propose the free formation energy of *CO_2 at the oxygen vacancy as the reactivity descriptor. By engineering the strain of the SnO(101) surface, the selectivity towards HCOOH can be further optimized at reduced overpotentials.

Associations between the Rorschach Ego Impairment Index and Measures on Intrapsychic and Interpersonal Functioning

The Rorschach Ego Impairment Index-2 (EII-2) has shown considerable validity as a measure of personality disturbance. However, few studies have been conducted on the associations between the EII-2 and measures related to ego strength and interpersonal capacities in mood and anxiety disorder patients. This study examined the strength of associations between the EII-2 and its subcomponents with measures of psychological suitability for psychotherapy, personality functioning, and interpersonal problems. A total of 315 outpatients with mood or anxiety disorders were assessed with the Rorschach Comprehensive System (RCS), comprising the EII-2, the Suitability for Psychotherapy Scale (SPS), the Inventory of Interpersonal Problems (IIP-64), and the Quality of Object Relations Scale (QORS), as part of a pre-treatment evaluation. The relatively weak associations found in the study between the EII-2 and the other measures were mostly in the hypothesized direction and often modified by personality pathology. Of the EII-2 subcomponents, the Good Human Representation (GHR) variable was associated with the SPS. The subcomponent Critical Contents were associated with the IIP and the subcomponent WSum6 with the IIP and QORS. Further research is needed to clarify whether the EII-2 has incremental validity in predicting the treatment outcome and alliance in comparison to interview-based and self-report measures.

Scaling Relation of the Scalar Diffusion in a Rotating Mixer

Scalar mixing is under the joint control of convection and diffusion.The ratio of the dissipative scale of velocity field to that of the scalar field depends on the Schmidt number.In the high Schmidt mumber limit.the scalar scale is much smaller than that of the momentum,which then reguires either special treat ment or ad hoc models for the sealar quantity in mumerical simulations.In order to avoid model uncertainty or unnecessary numerical complexity.the direct numerical simulation is performed for studying the scalar mixing process in a confined rotating mixer tank.It has been found that in the range of negligible mumerical diffusivity the characteristic scalar mixing time is inversely proportional to the scalar diffusivitv.Analysis based on the dimensional argument justifies such scaling relation as well.from which the unaccepted computational time of the nixing process in the high Schmidt number limit can be efficiently determined,without the use of ad hoc models This scaling idea is also of practical meaningfulness for ot her similar problems.

Computational design of catalysts for ammonia synthesis

Ammonia plays a crucial role in agriculture and chemical engineering,and acts as a promising carbon-free transportation fuel.Catalysts design is deemed as a key to solve the restriction of energy-intensive Haber-Bosch process of ammonia production.With the development of computational modeling,computation-aided catalyst design serves as one important driving force for material innovation,saving a lot of experimental efforts based on trial and error.Computational modeling not only provides fundamental mechanistic insights into the reaction with great details regarding adsorbate geometries,electronic structures,and elementary-step energies,but also expedites the material discovery with descriptor-based catalyst design,core of which is the establishment of thermo/kinetic scaling relations.In this review,we present firstly the mechanistic understanding of ammonia synthesis and transition state scaling relations developed on pure transition-metal catalysts.We then summarize catalysts design strategies guided by alloy,size,and magnetic effects with the goal of breaking the limitations set by scaling relations to achieve better catalytic performance.Finally,future opportunities and challenges associated with computation design of optimal catalysts for ammonia synthesis are outlined.

Study of spin sum rules (and the strong coupling constant at large distances)

We present recent results from Jefferson Lab on sum rules related to the spin structure of the nucleon. We then discuss how the Bjorken sum rule with its connection to the Gerasimov-Drell-Hearn sum, allows us to conveniently define an effective coupling for the strong force at all distances.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Fundamental knowledge of structure-activity correlations for heterogeneous single-atom catalysts(SACs)is essential in guiding catalytic design.While linear scaling relations are powerful for predicting the performance of traditionalmetal catalysts,they appear to fail with the involvement of SACs.Comparing the catalytic CO oxidation activity of different atomically dispersed metals(3d,4d,and 5d)in conjunction with computational modeling enabled us to establish multiple scaling relations between the activity and simply calculated descriptors.