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Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs
摘要： We report ultrafast optical measurements of the Dirac line-node semimetal ZrSiS and the Weyl semimetal NbAs, using mid-infrared pump photons from 86 meV to 500 meV to directly excite Dirac and Weyl fermions within the linearly dispersing bands. In NbAs, the photoexcited Weyl fermions initially form a non-thermal distribution, signi?ed by a brief spike in the differential re?ectivity whose sign is controlled by the relative energy of the pump and probe photons. In ZrSiS, electron-electron scattering rapidly thermalizes the electrons, and the spike is not observed. Subsequently, hot carriers in both materials cool within a few picoseconds. This cooling, as seen in the two materials’ differential re?ectivity, differs in sign, shape, and timescale. Nonetheless, we ?nd that it may be described in a simple model of thermal electrons, without free parameters. The electronic cooling in ZrSiS is particularly fast, which may make the material useful for optoelectronic applications.
关键词： ultrafast optical measurements,electronic cooling,photoexcitation,Dirac line-node semimetal,thermalization,Weyl semimetal
更新于2025-09-23 15:21:01
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Atmospheric response to the 20 March 2015 solar eclipse along the whole aerosol column by lidar measurements
摘要： Lidar measurements at 355, 532, and 1064 nm have been performed at Lecce (40.3°N, 18.1°E), in south-eastern Italy, to investigate for the first time the impact of the 20 March 2015 solar eclipse on both the planetary boundary layer (PBL) height and the aerosol optical and microphysical properties along the whole aerosol column. The partial solar eclipse lasted from 08:30 up to 10:47 UTC and reached the full phase at 09:37 UTC. The maximum percentage obscuration of the solar disk was 43.6%. The eclipse cooling effect was responsible at the full phase time (tF) for the downward solar irradiance decrease at the top of the atmosphere, at the surface, and within the atmosphere of 429.2 ± 0.6, 373 ± 25, and 56 ± 26 W m-2, respectively. The turbulent kinetic energy, the potential temperature flux, the sensible heat flux, the variance of air temperature, and the vertical wind speed at the surface revealed that the turbulence activity reached the maximum weakening at the time tF. The standard deviation (SD) technique has been applied to both the lidar range corrected signals (RCS) at 1064 nm and the linear volume depolarization ratio (δV) profiles at 355 nm to determine the time evolution of the shallow PBL height and the aloft aerosol layers. The SD technique applied to RCS and δV profiles revealed similar results within experimental uncertainties. The PBL height, which was equal to 380 ± 40 m above ground level (AGL) at the eclipse full phase (09:37 UTC), decreased up to 220 ± 20 m at 09:45 UTC because of the eclipse cooling effect, and then increased up to 320 ± 30 m at 10:17 UTC. The determined PBL height time evolution was in good agreement with the ones of the main turbulence parameters at the surface after tF. The vertical profiles of the aerosol backscatter coefficient (β), the δV at 355 nm, and the extinction-related ?ngstr?m exponent (?), calculated at the 355-1064 nm wavelength pair revealed a marked decrease of β, δV, and ? at the eclipse full phase, within the aloft aerosol layers. The abrupt β, δV, and ? decrease due to the aerosol concentration and type changes has mainly been associated with the decrease of the fine-mode particle contribution.
关键词： solar irradiance,Solar eclipse,lidar measurements,atmospheric aerosols,turbulence parameters,planetary boundary layer
更新于2025-09-23 15:21:01
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Five kHz thermometry in turbulent spray flames using chirped-probe-pulse femtosecond CARS, part II: Structure of reaction zones
摘要： Temperature was measured in turbulent spray flames of ethanol and acetone stabilized on the piloted Sydney Needle Spray Burner (SYNSBURN TM) using single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP-fs-CARS) with a repetition rate of 5 kHz. The burner features air-blast atomization of liquid injected from a needle that can be translated by a length Lr within a co-flowing air stream so that piloted spray flames ranging from dilute to dense can be studied. Part I of these investigations has reported on the CPP-fs-CARS technique and extensive details of data processing methodology. Part II is concerned with the structure of the reaction zones at different spray loadings and for different departures from blow-off. While not performed simultaneously, measurements of the size distribution of liquid fragments are also reported and discussed in conjunction with the measured temperature. Measured probability density functions of temperature show that for flames with the same liquid loading but different recess lengths, Lr, the near-field spray structure that forms upstream of x/D = 10 affects flame structure and stability further downstream. As the spray exiting the burner becomes denser, with a higher proportion of ligaments and 'irregular' shaped objects, the entrainment of hot pilot gases into the spray envelope is affected, hence changing the rates of vaporization and subsequent combustion. The reported results will also form a useful platform for validating sub-models of atomization and combustion in turbulent, dilute to dense spray flames.
关键词： Femtosecond-CARS,Temperature measurements,Turbulent spray flames
更新于2025-09-23 15:21:01
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Regionalization and Dynamic Parameterization of Quantum Yield of Photosynthesis to Improve the Ocean Primary Production Estimates From Remote Sensing
摘要： Quantum yield of photosynthesis (φ) expresses the efficiency of phytoplankton carbon fixation given certain amount of absorbed light. This photophysiological parameter is key to obtaining reliable estimates of primary production (PPsat) in the ocean based on remote sensing information. Several works have shown that φ changes temporally, vertically, and horizontally in the ocean. One of the primary factors ruling its variability is light intensity and thereby, it can be modeled as a function of Photosynthetically Available Radiation (PAR). We estimated φ utilizing long time-series collected in the North Subtropical Oligotrophic Gyres, at HOT and BATS stations (Pacific and Atlantic oceans, respectively). Subsequently the maximum quantum yield (φm) and Kφ (PAR value at half φm) were calculated. Median φm values were ～0.040 and 0.063 mol C mol photons?1 at HOT and BATS, respectively, with higher values in winter. Kφ values were ～8.0 and 10.8 mol photons m?2 d?1 for HOT and BATS, respectively. Seasonal variability in Kφ showed its peak in summer. Dynamical parameterizations for both regions are indicated by their temporal behaviors, where φm is related to temperature at BATS while Kφ to PAR, in both stations. At HOT, φm was weakly related to temperature and its median annual value was used for the whole data series. Differences in the study areas, even though both belong to Subtropical Gyres, reinforced the demand for regional parameterizations in PPsat models. Such parameterizations were finally included in a PPsat model based on phytoplankton absorption (PPsat?aphy?based), where results showed that the PPsat?aphy?based model coupled with dynamical parameterization improved PPsat estimates. Compared with PPsat estimates from the widely used VGPM, a model based on chlorophyll concentration (PPsat?chl?based), PPsat?aphy?based reduced model-measurement differences from ～62.8 to ～8.3% at HOT, along with well-matched seasonal cycle of PP (R2 = 0.76). There is not significant reduction in model-measurement differences between PPsat?chl?based and PPsat?aphy?based PP at BATS though (37.8 vs. 36.4%), but much better agreement in seasonal cycles with PPsat?aphy?based (R2 increased from 0.34 to 0.71). Our results point to improved estimation of PPsat by parameterized quantum yield along with phytoplankton absorption coefficient at the core.
关键词： quantum yield of photosynthesis,ocean color,phytoplankton primary production,in situ measurements,dynamical parameterization,marine seasonal variability
更新于2025-09-23 15:21:01
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Recent Progress in Quantitative Land Remote Sensing in China
摘要： During the past forty years, since the first book with a title mentioning quantitative and remote sensing was published [1], quantitative land remote sensing has advanced dramatically, and numerous books have been published since then [2–6] although some of them did not use quantitative land remote sensing in their titles. Quantitative land remote sensing has not been explicitly defined in the literature, but we consider it as a sub-discipline of remote sensing including the following components (see Figure 1): radiometric preprocessing, inversion, high-level product generation, and applications. Many inversion algorithms rely on physical models of radiation regimes of landscapes, which link with remotely-sensed data. Generating high-level satellite products of land surface biophysical and biochemical variables create the key bridge between remote sensing science and applications. Conducting in situ measurements for validation of inversion algorithms and satellite products is also a critical component. Application of satellite products to address scientific and societal relevant issues will ultimately decide the future of quantitative land remote sensing.
关键词： inversion algorithms,in situ measurements,land surface biophysical and biochemical variables,satellite data,quantitative land remote sensing
更新于2025-09-23 15:21:01
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Accurate measurements of line strengths and air-broadening coefficients in methane around 1.66?μm using cavity ring down spectroscopy
摘要： Accurate measurements of line strengths and air-broadening coefficients for 10 lines of 12CH4 mostly from the band (2ν2 + ν3) and 2 lines of 13CH4 from the band (2ν3) around 1.66 μm were performed using cavity ring down spectroscopy. Spectra of mixtures of 12CH4 in air with well-defined mole fractions of methane were recorded at pressures between 10 and 90 mbar at 296 K. The values of the line strength for 12CH4 lines were obtained with the uncertainty 1% and 2%, respectively. The uncertainties of the values of the air-broadening coefficient varied from 2 to 5% depending on the line. The values of the line strength and air-broadening coefficient for two methane isotopes obtained in this work were compared with the corresponding values from different experimental studies, as well as with the data given in HITRAN 2016 database.
关键词： Line intensity measurements,Cavity ring down spectroscopy,Methane,Infrared,Air-broadening coefficients
更新于2025-09-23 15:21:01
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All-carbon THz components based on laser-treated diamond
摘要： We report on fs laser structuring and graphitization of diamond and experimental characterization of its THz response. A full characterization of graphitized, conductive layer generated by laser irradiation is carried out by performing scanning-electron microscopy, Raman spectroscopy and electrical measurements. The transmittance of the laser textured diamond samples, both with the graphitic overlayer and after selective oxidizing etching, is analyzed in the (0.25 ÷ 6.0) THz spectral range. A significant selective absorption of the graphitized overlayer towards polarized THz radiation is demonstrated, which is associated to the formation of graphitic laser induced periodic surface structures. This anisotropy allows conceiving compact passive metasurfaces based on conductive/dielectric patterns on the diamond plate surface for the development of robust, lightweight and broadband THz optical components.
关键词： graphitic laser induced periodic surface structures,graphitization,electrical measurements,fs laser structuring,THz response,transmittance,THz optical components,polarized THz radiation,conductive layer,diamond,Raman spectroscopy,metasurfaces
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Investigating metal-semiconductor contacts in solar cells using magnetic field measurements
摘要： While solar cells and modules are already a mature technology in mass production, contacting schemes are constantly evolving. For example, multi busbar/multi wire contacting systems are currently being developed. During the development and the production of such technologies, it is critical to optimize and to systematically monitor their performance. In this paper, we find that different contacting fault types can be identified by inducing specific current flow patterns through the contacts of a single side of a solar cell and measuring the resultant 2D magnetic field image. Additionally, we explore the use of circuit network modelling in conjunction with these magnetic field images to gain further insights about the contacting schemes. Excellent agreement between circuit simulations and magnetic field measurements was achieved by combining different current flow patterns as demonstrated on a multi-wire contacted solar cell.
关键词： photovoltaic cells,circuit modelling,characterization,magnetic field measurements,SPICE
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Experimental Study of the Spectral and Angular Solar Irradiance
摘要： We developed an experimental set-up and procedure to measure spectral and angular solar irradiance to accurately predict and optimize solar power plant performance. The set-up is comprised of a fiber coupled spectrometer mounted to a rotational stage which allows for 360? light capture. The lightweight and flexible design enables irradiance measurements at any location. Measurements were taken in Enschede, Netherlands and in Phoenix, AZ, USA. We find a strong location, dependence of spectro-angular irradiance on the surroundings and cloud coverage which needs to be considered when modelling and optimizing location dependent solar power plant output.
关键词： spectral albedo,Bifacial solar cells,spectral and angular irradiance,solar irradiance measurements
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific) - Seogwipo-si, Korea (South) (2019.5.8-2019.5.10)] 2019 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific) - Optimal scheduling of critical peak pricing considering photovoltaic generation and electric vehicle load
摘要： For long-wavelength space-based radars, such as the P-band radar on the recently selected European Space Agency BIOMASS mission, system distortions (crosstalk and channel imbalance), Faraday rotation, and system noise all combine to degrade the measurements. A first-order analysis of these effects on the measurements of the polarimetric scattering matrix is used to derive differentiable expressions for the errors in the polarimetric backscattering coefficients in the presence of Faraday rotation. Both the amplitudes and phases of the distortion terms are shown to be important in determining the errors and their maximum values. Exact simulations confirm the accuracy and predictions of the first-order analysis. Under an assumed power-law relation between σhv and the biomass, the system distortions and noise are converted into biomass estimation errors, and it is shown that the magnitude of the deviation of the channel imbalance from unity must be 4–5 dB less than the crosstalk, or it will dominate the error in the biomass. For uncalibrated data and midrange values of biomass, the crosstalk must be less than ?24 dB if the maximum possible error in the biomass is to be within 20% of its true value. A less stringent condition applies if the amplitudes and phases of the distortion terms are considered random since errors near the maximum possible are very unlikely. For lower values of the biomass, the noise becomes increasingly important because the σhv signal-to-noise ratio is smaller.
关键词： Biomass,Faraday rotation,polarimetric measurements,system distortion,calibration,long-wavelength radar
更新于2025-09-23 15:19:57