The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter1, 2, 3, 4, 5. The strong time-periodic potential of intense laser light can be ...used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states, which are essential in realizing new photo-induced quantum phases6, 7, 8. Similarly, dressing of free-electron states near the surface of a solid generates Volkov states, which are used to study nonlinear optics in atoms and semiconductors9. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use time- and angle-resolved photoemission spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.
A mild and fully catalytic aryl-aryl cross coupling
gold-catalysed C-H activation has been achieved by merging gold and photoredox catalysis. The procedure is free of stoichiometric oxidants and ...additives, which were previously required in gold-catalysed C-H activation reactions. Exploiting dual gold and photoredox catalysis confers regioselectivity
the crucial gold-catalysed C-H activation step, which is not present in the unselective photocatalysis-only counterpart.
Forecasting the state of health and remaining useful life of Li-ion batteries is an unsolved challenge that limits technologies such as consumer electronics and electric vehicles. Here, we build an ...accurate battery forecasting system by combining electrochemical impedance spectroscopy (EIS)-a real-time, non-invasive and information-rich measurement that is hitherto underused in battery diagnosis-with Gaussian process machine learning. Over 20,000 EIS spectra of commercial Li-ion batteries are collected at different states of health, states of charge and temperatures-the largest dataset to our knowledge of its kind. Our Gaussian process model takes the entire spectrum as input, without further feature engineering, and automatically determines which spectral features predict degradation. Our model accurately predicts the remaining useful life, even without complete knowledge of past operating conditions of the battery. Our results demonstrate the value of EIS signals in battery management systems.
High silica (>70 wt.% SiO2) granites (HSGs) are important carriers of highly incompatible elements, thus, understanding their origin is relevant to understanding how the composition of the ...continental crust evolves. We examined a large-scale geochemical study of plutons in the Peninsular Ranges Batholith in southern California (USA) to better understand the petrogenetic relationships between HSGs and the batholith. Using highly incompatible and compatible elements, we show that HSGs represent residual liquids within a felsic (69–72 wt.% SiO2) magmatic crystal mush at crystal fractions of 50–60% and residual liquid fractions of 40–50%. Trace element systematics show that separation of the HSG liquid from the crystal mush is inefficient, such that no more than 70–80% of the HSG is fully extracted and the remaining greater than 20–30% remains trapped in cumulate mush. We find little evidence of more efficient liquid–crystal segregation, which suggests that compaction-induced segregation may be too slow to be important on a large scale. Instead, the terminal porosity of 20–30% coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension (∼0.74), which may indicate that crystal settling – perhaps in the form of hindered settling – drives segregation of viscous silicic melts and crystals. Unlike compaction, settling operates on timescales of 1–10 ky, fast enough to generate large volumes of HSG and complementary cumulates with trapped melt before magma chambers freeze. Many felsic plutons may thus be cumulates, but because of trapped melt, they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent. The approach here, using a combination of highly incompatible and compatible elements, provides a way of identifying and quantifying trapped melt fractions. Finally, we show that HSGs appear to form only in the shallow crust (<10 km) and rarely in the middle to lower crust. Where HSGs are common, mafic magmas are common too, suggesting a genetic relationship between the two. If HSGs derive by crystal fractionation of basaltic parents, they represent at most 5% of the original mass of parental magma, but because they form almost exclusively at low pressures, they may be over-represented in shallowly exhumed batholiths. Why HSGs form primarily in the upper crust is unclear.
•High silica granites are residual liquids after crystallization from a felsic parental magma.•Some felsic plutons are cumulates, but are geochemically similar to magmas because of trapped melt.•The terminal amount of trapped melt in felsic cumulates is no less than 20–30%.•Terminal trapped melt fraction corresponds to critical packing density.•Felsic cumulates formed by crystal settling not compaction.
Sensory processing is dependent upon behavioral state. In mice, locomotion is accompanied by changes in cortical state and enhanced visual responses. Although recent studies have begun to elucidate ...intrinsic cortical mechanisms underlying this effect, the neural circuits that initially couple locomotion to cortical processing are unknown. The mesencephalic locomotor region (MLR) has been shown to be capable of initiating running and is associated with the ascending reticular activating system. Here, we find that optogenetic stimulation of the MLR in awake, head-fixed mice can induce both locomotion and increases in the gain of cortical responses. MLR stimulation below the threshold for overt movement similarly changed cortical processing, revealing that MLR’s effects on cortex are dissociable from locomotion. Likewise, stimulation of MLR projections to the basal forebrain also enhanced cortical responses, suggesting a pathway linking the MLR to cortex. These studies demonstrate that the MLR regulates cortical state in parallel with locomotion.
•Locomotion induces changes in cortical state and visual processing in mice•Optogenetic stimulation of mesencephalic locomotor region (MLR) initiates locomotion•Subthreshold stimulation of MLR induces cortical changes in the absence of locomotion•The MLR projection to basal forebrain provides a circuit to link locomotion to cortex
Running has previously been shown to induce changes in visual cortical processing in the mouse. In this study, Lee et al. identify the neural circuit in the mesencephalic locomotor region that initially couples locomotion with cortical changes.
We analyse the relationship between geopolitical risk and asset prices and show that geopolitical risk is distinct from existing measures of economic, financial, and political risk and that the ...response of precious metals to geopolitical risk differs considerably from that of other assets. Precious metals are hedges against geopolitical risk in general and geopolitical threats (as opposed to acts) in particular. Conversely, stocks and bonds respond negatively to geopolitical risk and geopolitical threats. For extreme geopolitical risks, only gold and silver display consistent safe haven properties. Our results show that holding precious metals within a diversified portfolio lowers the impact of geopolitical risk.
It has become almost paradigmatic in the coral reef literature that fishing-induced reductions of parrotfish abundance cause benthic phase shifts from coral to macroalgal dominance. This study ...examined the alternatives of top-down control of the benthos by parrotfish density and bottom-up control of parrotfish density by the benthos at four Philippine islands in a long-term (7.5–30 years) “natural experiment”. No-take marine reserves (NTMRs) demonstrated that fishing reduced parrotfish density significantly at two islands (Sumilon, Mantigue), but not significantly at two other islands (Apo, Selinog). There was no evidence that cover of hard coral decreased, nor macroalgal cover increased, in fished areas relative to NTMRs, no evidence that parrotfish density affected hard coral cover significantly, and thus no evidence of top-down, fishing-induced benthic phase shifts at all four islands. There was, however, compelling evidence that benthos (cover of dead substrata and hard coral) exerted strong bottom-up control on parrotfish density. This bottom-up control was demonstrated most clearly by major environmental disturbances (e.g. typhoons, coral bleaching) that changed benthic habitat and, subsequently, parrotfish density. As hard coral cover declined (and cover of dead substratum increased), parrotfish density increased and vice versa. This response occurred in both major parrotfish feeding guilds (scrapers and excavators). This long-term study on heavily fished coral reefs suggests that the benthos drives the parrotfish, not the other way around. The paradigm of fishing-induced benthic phase shifts may not apply to all coral reefs at all times. Multiple drivers of benthic change on coral reefs should always be considered.
This paper investigates a symbiotic unmanned aerial vehicle (UAV)-assisted intelligent reflecting surface (IRS) radio system, where the UAV is leveraged to help the IRS reflect its own signals to the ...base station, and meanwhile enhance the UAV transmission by passive beamforming at the IRS. First, we consider the weighted sum bit error rate (BER) minimization problem among all IRSs by jointly optimizing the UAV trajectory, IRS phase shift matrix, and IRS scheduling, subject to the minimum primary rate requirements. To tackle this complicated problem, a relaxation-based algorithm is proposed. We prove that the converged relaxation scheduling variables are binary, which means that no reconstruct strategy is needed, and thus the UAV rate constraints are automatically satisfied. Second, we consider the fairness BER optimization problem. We find that the relaxation-based method cannot solve this fairness BER problem since the minimum primary rate requirements may not be satisfied by the binary reconstruction operation. To address this issue, we first transform the binary constraints into a series of equivalent equality constraints. Then, a penalty-based algorithm is proposed to obtain a suboptimal solution. Numerical results are provided to evaluate the performance of the proposed designs under different setups, as compared with benchmarks.
In this letter, we investigate the downlink performance of massive multiple-input multiple-output (MIMO) systems where the base station is equipped with one-bit analog-to-digital/digital-to-analog ...converters (ADC/DACs). We assume that the base station employs the linear minimum mean-squared-error channel estimator and treats the channel estimate as the true channel to precode the data symbols. We derive an expression for the downlink achievable rate for matched-filter precoding. A detailed analysis of the resulting power efficiency is pursued using our expression of the achievable rate. Numerical results are presented to verify our analysis. In particular, it is shown that, compared with conventional massive MIMO systems, the performance loss in one-bit massive MIMO systems can be compensated for by deploying approximately 2.5 times more antennas at the BS.
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