Explore the vast range of titles available.

The advent of ultrafast laser science offers the unique opportunity to combine Floquet engineering with extreme time resolution, further pushing the optical control of matter into the petahertz domain. However, what is the shortest driving pulse for which Floquet states can be realised remains an unsolved matter, thus limiting the application of Floquet theory to pulses composed by many optical cycles. Here we ionized Ne atoms with few-femtosecond pulses of selected time duration and show that a Floquet state can be observed already with a driving field that lasts for only 10 cycles. For shorter pulses, down to 2 cycles, the finite lifetime of the driven state can still be explained using an analytical model based on Floquet theory. By demonstrating that the amplitude and number of Floquet-like sidebands in the photoelectron spectrum can be controlled not only with the driving laser pulse intensity and frequency, but also by its duration, our results add a new lever to the toolbox of Floquet engineering. Floquet engineering aims at inducing new properties in materials with light. Here the authors have used pulses of variable durations, to investigate its applicability in the femtosecond domain. Surprisingly, they found that it holds to the few-cycle limit.

Dryland, which mainly retains rain-fed agriculture, is the main type of farmland in China and widely distributed in the northern regions. Rainfall scarcity limits the development of maize at the seedling stage, which adversely affects the increase in maize yields in this region. A planting method that allows variable sowing depths based on the uneven distribution of soil moisture was proposed in this study. This site-specific planting method which fully utilizes available soil water is able to overcome the above problem. The framework of variable depth seeding suitable for this region was constructed: Within the depth range of 5.5 to 8.5 cm in the soil, maize seeds should be sown to a position with a relative soil moisture of 70%. For some drylands without such moisture conditions, seeds can be placed at the position with the highest relative soil moisture in this depth range. Taking the conventional planting method as the control group, the performance of the variable depth planting method in improving maize seedling growth was evaluated. The results showed that the proposed planting method not only increased the emergence rate and the seedling uniformity by 9.31% and 25.29%, respectively, but also raised the mean leaf number and the mean plant height in the same growth period, having a remarkable effect in improving the maize seedling traits. This planting method is easy to be embedded into precision control systems of the maize planter, and will promote the application of soil moisture-based planting technology and thus increase the yield per hectare of maize.

Isolated attosecond pulse (IAP) generation usually involves the use of short-medium gas cells operated at high pressures. In contrast, long-medium schemes at low pressures are commonly perceived as inherently unsuitable for IAP generation due to the nonlinear phenomena that challenge favourable phase-matching conditions. Here we provide clear experimental evidence on the generation of isolated extreme-ultraviolet attosecond pulses in a semi-infinite gas cell, demonstrating the use of extended-medium geometries for effective production of IAPs. To gain a deeper understanding we develop a simulation method for high-order harmonic generation (HHG), which combines nonlinear propagation with macroscopic HHG solving the 3D time-dependent Schrödinger equation at the single-atom level. Our simulations reveal that the nonlinear spatio-temporal reshaping of the driving field, observed in the experiment as a bright plasma channel, acts as a self-regulating mechanism boosting the phase-matching conditions for the generation of IAPs.

Employees’ innovative behavior is a vital source for promoting the sustainable survival and development of enterprises. Innovation is a complicated and high-risk mental process, where in each stage employees’ innovative attitude and behavior will be affected by the varying behaviors of their direct leaders. Therefore, exploring the intricate relationship between leadership behavior and employees’ innovative behavior is necessary. Based on social exchange theory, this study builds a cross-level moderation model to investigate the impact of ethical leadership on employees’ innovative behavior and the mediating role of organization-based self-esteem and the moderating role of flexible human resource management. On the basis of a questionnaire survey of 146 supervisors and 365 subordinates in the mainland of China, the empirical results show that: (a) Ethical leadership positively affects employees’ innovative behavior significantly; (b) Organization-based self-esteem has a partial mediating relationship between ethical leadership and employees’ innovative behavior; and (c) flexible human resource management plays a positive moderating role in the relationship between organization-based self-esteem and employees’ innovative behavior, and it also positively moderates the mediating effect of organization-based self-esteem on the relationship between ethical leadership and employees’ innovative behavior. The findings reveal the internal mechanism and boundary condition of ethical leadership influencing employees’ innovative behavior, which provide a reference for enterprises to encourage employees to innovate, and have important practical significance for employees to actively pursue innovative activities in the workplace.

The exposure of molecules to attosecond extreme-ultraviolet (XUV) pulses offers a unique opportunity to study the early stages of coupled electron–nuclear dynamics in which the role played by the different degrees of freedom is beyond standard chemical intuition. We investigate, both experimentally and theoretically, the first steps of charge-transfer processes initiated by prompt ionization in prototype donor– π –acceptor molecules, namely nitroanilines. Time-resolved measurement of this process is performed by combining attosecond XUV-pump/few-femtosecond infrared-probe spectroscopy with advanced many-body quantum chemistry calculations. We show that a concerted nuclear and electronic motion drives electron transfer from the donor group on a sub-10-fs timescale. This is followed by a sub-30-fs relaxation process due to the probing of the continuously spreading nuclear wave packet in the excited electronic states of the molecular cation. These findings shed light on the role played by electron–nuclear coupling in donor– π –acceptor systems in response to photoionization. The first steps of charge transfer in molecules after their interaction with light occur on an ultrafast timescale. Now, by combining attosecond pump/few-femtosecond probe spectroscopy with quantum chemistry calculations, it has been shown that a concerted nuclear and electronic motion drives electron transfer in donor– π –acceptor molecules on a sub-10-fs timescale.

The advent of ultrafast laser science offers the unique opportunity to combine Floquet engineering with extreme time resolution, further pushing the optical control of matter into the petahertz domain. However, what is the shortest driving pulse for which Floquet states can be realised remains an unsolved matter, thus limiting the application of Floquet theory to pulses composed by many optical cycles. Here we ionized Ne atoms with few-femtosecond pulses of selected time duration and show that a Floquet state can be established already within 10 cycles of the driving field. For shorter pulses, down to 2 cycles, the finite lifetime of the driven state can still be explained using an analytical model based on Floquet theory. By demonstrating that the population of the Floquet sidebands can be controlled not only with the driving laser pulse intensity and frequency, but also by its duration, our results add a new lever to the toolbox of Floquet engineering.

The electronic energy levels of cyclo(Glycine-Phenylalanine), cyclo(Tryptophan-Tyrosine) and cyclo(Tryptophan-Tryptophan) dipeptides are investigated with a joint experimental and theoretical approach. Experimentally, valence photoelectron spectra in the gas phase are measured using VUV radiation. Theoretically, we first obtain low-energy conformers through an automated conformer-rotamer ensemble sampling scheme based on tight-binding simulations. Then, different first principles computational schemes are considered to simulate the spectra: Hartree-Fock (HF), density functional theory (DFT) within the B3LYP approximation, the quasi--particle GW correction, and the quantum-chemistry CCSD method. Theory allows to assign the main features of the spectra. A discussion on the role of electronic correlation is provided, by comparing computationally cheaper DFT scheme (and GW) results with the accurate CCSD method.

Natural photosynthesis proceeded by sequential water splitting and CO 2 reduction reactions is an efficient strategy for CO 2 conversion. Here, mimicking photosynthesis to boost CO 2 -to-CO conversion is achieved by using plasmonic Bi as an electron-proton-transfer mediator. Electroreduction of H 2 O with a Bi electrode simultaneously produces O 2 and hydrogen-stored Bi (Bi-H x ). The obtained Bi-H x is subsequently used to generate electron-proton pairs under light irradiation to reduce CO 2 to CO; meanwhile, Bi-H x recovers to Bi, completing the catalytic cycle. This two-step strategy avoids O 2 separation and enables a CO production efficiency of 283.8 μmol g −1 h −1 without sacrificial reagents and cocatalysts, which is 9 times that on pristine Bi in H 2 gas. Theoretical/experimental studies confirm that such excellent activity is attributed to the formed Bi-H x intermediate that improves charge separation and reduces reaction barriers in CO 2 reduction. Using a single catalyst to mimic the two-step photosynthesis for CO 2 conversion remains a challenge. Here, the authors report a simple Bi catalyst that can act as an electron-proton-transfer mediator to spatially and temporally separate H2 O splitting and CO 2 reduction reactions in CO 2 -to-CO conversion process.

A bstract We present an efficient method to shorten the analytic integration-by-parts (IBP) reduction coefficients of multi-loop Feynman integrals. For our approach, we develop an improved version of Leinartas’ multivariate partial fraction algorithm, and provide a modern implementation based on the computer algebra system Singular. Furthermore, we observe that for an integral basis with uniform transcendental (UT) weights, the denominators of IBP reduction coefficients with respect to the UT basis are either symbol letters or polynomials purely in the spacetime dimension D . With a UT basis, the partial fraction algorithm is more efficient both with respect to its performance and the size reduction. We show that in complicated examples with existence of a UT basis, the IBP reduction coefficients size can be reduced by a factor of as large as ∼ 100. We observe that our algorithm also works well for settings without a UT basis.