Learning the optimal power flow:Environment design matters

To solve the optimal power flow(OPF)problem,reinforcement learning(RL)emerges as a promising new approach.However,the RL-OPF literature is strongly divided regarding the exact formulation of the OPF problem as an RL environment.In this work,we collect and implement diverse environment design decisions from the literature regarding training data,observation space,episode definition,and reward function choice.In an experimental analysis,we show the significant impact of these environment design options on RL-OPF training performance.Further,we derive some first recommendations regarding the choice of these design decisions.The created environment framework is fully open-source and can serve as a benchmark for future research in the RL-OPF field.

Two-photon emission from a superlattice-based superconducting light-emitting structure

Superconductor-semiconductor hybrid devices can bridge the gap between solid-state-based and photonics-based quantum systems,enabling new hybrid computing schemes,offering increased scalability and robustness.One example for a hybrid device is the superconducting light-emitting diode(SLED).SLEDs have been theoretically shown to emit polarization-entangled photon pairs by utilizing radiative recombination of Cooper pairs.However,the twophoton nature of the emission has not been shown experimentally before.We demonstrate two-photon emission in a GaAs/AlGaAs SLED.Measured electroluminescence spectra reveal unique two-photon superconducting features below the critical temperature(Tc),while temperature-dependent photon-pair correlation experiments(g(2)(τ,T))demonstrate temperature-dependent time coincidences below Tc between photons emitted from the SLED.Our results pave the way for compact and efficient superconducting quantum light sources and open new directions in light-matter interaction studies.

The stability of carbon from a maize-derived hydrochar as a function of fractionation and hydrothermal carbonization temperature in a Podzol

Hydrochar(HC)produced by the hydrothermal carbonization(HTC)of typically wet biomass is generally considered to be less effective for carbon(C)sequestration in soils compared to biochar(BC)by pyrolysis,due to a higher content of more easily decomposable C.Although the recalcitrance of HC is suggested to improve with increasing HTC production temperature,the way it interacts and becomes associated with soil organic matter(SOM)fractions of different stabilities against decomposition,may also influence its effectiveness for C sequestration in soils.In that respect,this study aimed to verify the potential of HCs from maize silage produced at different HTC temperatures(190,210 and 230℃)for C sequestration in a HC-amended sandy loam Podzol.To do this,we conducted a pot trial experiment and traced the fate of HC-derived C(HC-C)within different SOM fractions,namely the free-and occluded particulate organic matter(POMF and POMO,respectively)fractions and that comprising organic matter(OM)bound to clays(OMCl).Approx.1 year after applying 5%of the different HTC temperature HCs to the soil,the SOM fractions were isolated by density fractionation for each HC treatment(HC190,HC210 and HC230)and the control(absent of HC).All fractions and the HCs were analyzed for organic C(OC)content and isotopic signatures(δ^(13)C).From the δ^(13)C signatures,the amount of HC-C and native soil organic carbon(SOC)within each fraction was calculated.Increased C contents and decreased H/C and O/C ratios were observed with increasing HTC production temperatures,which sug-gests a lower stability for the low temperature HC.After ca.1 year,a loss of~20-23%of the bulk soil TOC was found in the HC-amended soils.The POMF fraction of the HC-amended soils showed losses of 68-81%HC-C and 52-72%native SOC,which may be due to a positive priming effect caused by HC addition.The POM_(O) and OM_(Cl) fractions of the HC-amended soils contained more OC than the control,indicating the integration of HC-C together with SOM within these more stable fractions,while the effect of HTC production temperature on the level of decomposition of the resultant HCs was negligible.In all HC treatments,the OM_(Cl) fraction comprised the least amount of HC-C,thus showing the weakest response to C amendment.In conclusion,long(er)-term research on the C net balance that accounts for the observed priming-induced TOC losses and the HC-C enrichment in more stable fractions is required to verify the potential of the different HCs for the purpose of C sequestration in soils.

An investigation of the effects of hydrochar application rate on soil amelioration and plant growth in three diverse soils

The hydrothermal carbonization(HTC)of biogas digestate alters the raw materials inherent characteristics to produce a carbon(C)-rich hydrochar(HC),with an improved suitability for soil amelioration.Numerous studies report conflicting impacts of various HC application rates on soil properties and plant growth.In this study,the influence of HC application rate on soil improvement and plant growth aspects was investigated in three diverse soils(Chernozem,Podzol,and Gleysol).Pot trials were conducted in which all soils were amended with 5,10,20 and 30%(w/w)HC in quintuplicate,with two controls of pure soil(with and without plants,respectively)also included.Prior to potting,soil samples were collected from all HC-amended soils and controls and analyzed for soil pH,plant available nutrients(PO4-P and K),and microbial activity using standard laboratory and statistical methods.Immediately after potting,a 6-week seed germination experiment using Chinese cabbage was conducted to determine germination success,followed by a plant growth experiment of equal duration and plant species to determine biomass success.At the end of the study(after a total plant growth period of 12 weeks),each pot was sampled and comparatively analyzed for the same soil properties as at the beginning of the study.Soil pH shifted toward the pH of the HC(6.6)in all soils over the course of the study,but was most expressed in the 20%and 30%application rates,confirming the well-documented liming effect of HC.The addition of HC increased the PO4-P and K contents,particularly with 20%and 30%HC amendments.These results are proposedly due to the large labile C fraction of the HC,which is easily degradable by microorganisms.The rapid decomposition of this C fraction prompted the quick release of the HCs inherently high PO4-P and K content into the soil,and in turn,further stimulated microbial activity,until this fraction was essentially depleted.HC addition did not inhibit seed germination at any rate,presumably due to a lack of phytotoxic compounds in the HC from aging and microbial processes,and furthermore,showed no significant impact(positive or negative)on plant growth in any soil,despite improved soil conditions.In conclusion,although less pronounced,soil improvements were still achievable and maintainable at lower application rates(5%and 10%),whereas higher rates did not ensure greater benefits for plant growth.While the addition of high rates of HC did not detrimentally effect soil quality or plant growth,it could lead to leaching if the nutrient supply exceeds plant requirements and the soil’s nutrient retention capacity.Therefore,this study validates the previous study in the effectiveness of the biogas digestate HC for soil amelioration and suggests that smaller regularly repeated HC applications may be recommendable for soil improvement.

Observing charge separation in nanoantennas via ultrafast point-projection electron microscopy

Observing the motion of electrons on their natural nanometer length and femtosecond time scales is a fundamental goal of and an open challenge for contemporary ultrafast science1–5.At present,optical techniques and electron microscopy mostly provide either ultrahigh temporal or spatial resolution,and microscopy techniques with combined space-time resolution require further development6–11.In this study,we create an ultrafast electron source via plasmon nanofocusing on a sharp gold taper and implement this source in an ultrafast point-projection electron microscope.This source is used in an optical pump—electron probe experiment to study ultrafast photoemissions from a nanometer-sized plasmonic antenna12–15.We probe the real space motion of the photoemitted electrons with a 20-nm spatial resolution and a 25-fs time resolution and reveal the deflection of probe electrons by residual holes in the metal.This is a step toward time-resolved microscopy of electronic motion in nanostructures.

Spatial and spectral mode mapping of a dielectric nanodot by broadband interferometric homodyne scanning near-field spectroscopy

We investigate the optical properties of nanostructures of antimony sulfide(Sb2S3),a direct-bandgap semiconductor material that has recently sparked considerable interest as a thin film solar cell absorber.Fabrication from a nanoparticle ink solution and two-and three-dimensional nanostructuring with pattern sizes down to 50 nm have recently been demonstrated.Insight into the yet unknown nanoscopic optical properties of these nanostructures is highly desired for their future applications in nanophotonics.We implement a spectrally broadband scattering-type near-field optical spectroscopy technique to study individual Sb2S3 nanodots with a 20-nm spatial resolution,covering the range from 700 to 900 nm.We show that in this below-bandgap range,the Sb2S3 nanostructures act as high-refractive-index,low-loss waveguides with mode profiles close to those of idealized cylindrical waveguides,despite a considerable structural disorder.In combination with their high above-bandgap absorption,this makes them promising candidates for applications as dielectric metamaterials,specifically for ultrafast photoswitching.

Long-lived electron emission reveals localized plasmon modes in disordered nanosponge antennas

We report long-lived,highly spatially localized plasmon states on the surface of nanoporous gold nanoparticles—nanosponges—with high excitation efficiency.It is well known that disorder on the nanometer scale,particularly in two-dimensional systems,can lead to plasmon localization and large field enhancements,which can,in turn,be used to enhance nonlinear optical effects and to study and exploit quantum optical processes.Here,we introduce promising,three-dimensional model systems for light capture and plasmon localization as gold nanosponges that are formed by the dewetting of gold/silver bilayers and dealloying.We study light-induced electron emission from single nanosponges,a nonlinear process with exponents of n≈5...7,using ultrashort laser pulse excitation to achieve femtosecond time resolution.The long-lived electron emission process proves,in combination with optical extinction measurements and finite-difference time-domain calculations,the existence of localized modes with lifetimes of more than 20 fs.These electrons couple efficiently to the dipole antenna mode of each individual nanosponge,which in turn couples to the far-field.Thus,individual gold nanosponges are cheap and robust disordered nanoantennas with strong local resonances,and an ensemble of nanosponges constitutes a meta material with a strong polarization independent,nonlinear response over a wide frequency range.

Revealing true coupling strengths in two-dimensional spectroscopy with sparsity-based signal recovery

Two-dimensional(2D)spectroscopy is used to study the interactions between energy levels in both the field of optics and nuclear magnetic resonance(NMR).Conventionally,the strength of interaction between two levels is inferred from the value of their common off-diagonal peak in the 2D spectrum,which is termed the cross peak.However,stronger diagonal peaks often have long tails that extend into the locations of the cross peaks and alter their values.Here,we introduce a method for retrieving the true interaction strengths by using sparse signal recovery techniques and apply our method in 2D Raman spectroscopy experiments.

Electronic fingerprint mechanism of NO_(x) sensor based on single-material SnP_(3) logical junction

An extraordinary sensing ability of the SnP3-based single-material logical junction for harmful NO_(x)gases was explored in the present work through a set of first-principles electronic structure calculations.As a sensing platform,a metal-semiconductor-metal lateral junction composed of a single material was designed based on the metallic/semiconducting characteristics of trilayer/monolayer SnP_(3).Lacking a Schottky barrier at the electrode-channel interface,the gas-specific charge transfer between the SnP_(3) layer and gas molecules was precisely detected based on the current-voltage characteristics.NO_(x)gases with strong adsorption strength and charge transfer amount on the SnP_(3)substrate were shown to be particularly well detected in this manner,in terms of either the absolute magnitude of the current or negative differential resistance(NDR)at a reasonably small bias voltage as a sensing signal.This work will provide a new pathway to design a Schottky barrier-free metal-semiconductor junction for highly sensitive sensor applications.