The design of artificial molecular machines often takes inspiration from macroscopic machines. However, the parallels between the two systems are often only superficial, because most molecular ...machines are governed by quantum processes. Previously, rotary molecular motors powered by light and chemical energy have been developed. In electrically driven motors, tunnelling electrons from the tip of a scanning tunnelling microscope have been used to drive the rotation of a simple rotor in a single direction and to move a four-wheeled molecule across a surface. Here, we show that a stand-alone molecular motor adsorbed on a gold surface can be made to rotate in a clockwise or anticlockwise direction by selective inelastic electron tunnelling through different subunits of the motor. Our motor is composed of a tripodal stator for vertical positioning, a five-arm rotor for controlled rotations, and a ruthenium atomic ball bearing connecting the static and rotational parts. The directional rotation arises from sawtooth-like rotational potentials, which are solely determined by the internal molecular structure and are independent of the surface adsorption site.
A range of artificial molecular systems has been created that can exhibit controlled linear and rotational motion. In the further development of such systems, a key step is the addition of ...communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching when applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated when in a hexagonal rotor network on a Cu(111) surface by applying biases above 1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degeneracy of the ground-state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors can occur, resulting in the rotator arms pointing in different directions. Analysis reveals that the rotator arm directions are not random, but are coordinated to minimize energy via crosstalk among the rotors through dipolar interactions.
An extensive redistribution of spin density in TBrPP-Co molecules adsorbed on a Cu(111) surface is investigated by monitoring Kondo resonances at different locations on single molecules. Remarkably, ...the width of the Kondo resonance is found to be much larger on the organic ligands than on the central cobalt atom-reflecting enhanced spin-electron interactions on molecular orbitals. This unusual effect is explained by means of first-principles and numerical renormalization-group calculations highlighting the possibility to engineer spin polarization by exploiting interfacial charge transfer.
We present a comparison of the measured cosmic ray (CR) muon fluxes from two identical portable low‐cost detectors at different geolocations and their sensitivity to space weather events in real ...time. The first detector is installed at Mount Wilson Observatory, CA, USA (geomagnetic cutoff rigidity Rc ∼ 4.88 GV), and the second detector is running on the downtown campus of Georgia State University in Atlanta, GA, USA (Rc ∼ 3.65 GV). The variation of the detected muon fluxes is compared to the changes in the interplanetary solar wind parameters at the L1 Lagrange point and geomagnetic indexes. In particular, we have investigated the muon flux behavior during three major interplanetary shock events and geomagnetic disturbances that occurred during July and August of 2022. To validate the interpretation of the measured muon signals, we compare the muon fluxes to the measurement from the Oulu neutron monitor (NM, Rc ∼ 0.8 GV). The results of this analysis show that the muon detector installed at Mount Wilson Observatory demonstrates a stronger correlation with a high‐latitude NM. Both detectors typically observe a muon flux decrease during the arrival of interplanetary shocks and geomagnetic storms. Interestingly, the decrease could be observed several hours before the onset of the first considered interplanetary shocks at L1 at 2022‐07‐23 02:28:00 UT driven by the high‐speed Coronal Mass Ejection and related geomagnetic storm at 2022‐07‐23 03:59:00 UT. This effort represents an initial step toward establishing a global network of portable low‐cost CR muon detectors for monitoring the sensitivity of muon flux changes to space and terrestrial weather parameters.
Plain Language Summary
A pair of identical, low‐cost, and portable cosmic ray (CR) muon detectors is set up over 3,500 km apart for an exploratory study of monitoring space and terrestrial weather in real time at a global scale. One detector is installed on Mount Wilson, California and the other is in downtown Atlanta, Georgia. To validate the interpretation of the measured muon signals, the muon fluxes are compared to the well‐known neutron flux measurement from the Oulu neutron station in Finland. The results of this analysis show that the CR flux from both muon detectors typically decreases during geomagnetic storm events and that the muon detector installed on Mount Wilson is significantly correlated with the Oulu neutron monitor. Although this is yet an initial effort of building a global network of CR muon detectors for monitoring the space and earth weather in real time, the study provides evidence that muon network detection efficiency can be sufficient for a diagnostic of the major geoeffective space weather events.
Key Points
A global network of portable muon detectors is under development for monitoring the dynamic changes of the space and terrestrial weather
A comparison of the measured cosmic ray (CR) muon fluxes from two identical detectors at different geolocations in real‐time is carried out
A correlation study between the muon data and the neutron measurement at Oulu CR station in Finland is presented in this paper
Process of enhancing testing-capacity regarding COVID-19 is a topic of interest. This task of enhancing is constrained by socio-economic background of a country either in favorable or unfavorable ...ways. In this paper, we investigate timing of enhancing testing-capacity as an optimal problem, where the enhancement is quantified via number of tests as an instant measure and recovered portion as a long-term measure. The proposed work is structured analogous to an optimal machine replacement model based on a non-linear integral equation. Overall model is partially identifiable and compatible parameter estimations are carried out for a specific case study covering an early stage scenario. In addition, scenario development criteria on demand and effort for enhancing testing-capacity are introduced for predictions. In one numerical experiment, it is observed that frequency of enhancing testing-capacity starts decreasing after two increments indicating a favorable direction amidst effort constraints.
•Enhancing testing-capacity of COVID-19 is a process that needs monitoring.•Timing for enhanced testing can be modeled as an optimal replacement model.•Parameter estimation under different scenarios paves the way for process planning.
A collection of oscillatory basis functions generated via an integral equation is investigated here. This is a new approach in the harmonic analysis as we are able to interpret phenomena with damping ...and amplifying oscillations other than classical Fourier-like periodic waves. The proposed technique is tested with a data set of dengue incidence, where different types of influences prevail. An intermediate transform supported by the Laplace transform is available. It facilitates parameter estimation and strengthens the extraction of hidden influencing accumulations. This mechanistic work can be extended as a tool in signal processing that encounters oscillatory and accumulated effects.
Internal photoemission (IP) correlates with processes in which carriers are photoexcited and transferred from one material to another. This characteristic allows characterizing the properties of the ...heterostructure, for example, the band parameters of a material and the interface between two materials. IP also involves the generation and collection of photocarriers, which leads to applications in the photodetectors. This review discusses the generic IP processes based on heterojunction structures, characterizing p -type band structure and the band offset at the heterointerface, and infrared photodetection including a novel concept of photoresponse extension based on an energy transfer mechanism between hot and cold carriers.
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