Radiation Yield Research Articles

The impact of UV variability on the abundance of bright galaxies at z ≥ 9

ABSTRACT JWST observations have revealed a population of galaxies bright enough that potentially challenge standard galaxy formation models in the Λ cold dark matter (ΛCDM) cosmology. Using a minimal empirical framework, we investigate the influence of variability on the rest-frame ultra-violet (UV) luminosity function of galaxies at z ≥ 9. Our study differentiates between the median UV radiation yield and the variability of UV luminosities of galaxies at a fixed dark matter halo mass. We primarily focus on the latter effect, which depends on halo assembly and galaxy formation processes and can significantly increase the abundance of UV-bright galaxies due to the upscatter of galaxies in lower-mass haloes. We find that a relatively low level of variability, σUV ≈ 0.75 mag, matches the observational constraints at z ≈ 9. However, increasingly larger σUV is necessary when moving to higher redshifts, reaching $\sigma _{\rm UV} \approx 2.0\, (2.5)\, {\rm mag}$ at z ≈ 12 (16). This implied variability is consistent with expectations of physical processes in high-redshift galaxies such as bursty star formation and dust clearance during strong feedback cycles. Photometric constraints from JWST at z ≳ 9 therefore can be reconciled with a standard ΛCDM-based galaxy formation model calibrated at lower redshifts without the need for adjustments to the median UV radiation yield.

Single-Exciton Photoluminescence in a GaN Monolayer inside an AlN Nanocolumn.

GaN/AlN heterostructures with thicknesses of one monolayer (ML) are currently considered to be the most promising material for creating UVC light-emitting devices. A unique functional property of these atomically thin quantum wells (QWs) is their ability to maintain stable excitons, resulting in a particularly high radiation yield at room temperature. However, the intrinsic properties of these excitons are substantially masked by the inhomogeneous broadening caused, in particular, by fluctuations in the QWs' thicknesses. In this work, to reduce this effect, we fabricated cylindrical nanocolumns of 50 to 5000 nm in diameter using GaN/AlN single QW heterostructures grown via molecular beam epitaxy while using photolithography with a combination of wet and reactive ion etching. Photoluminescence measurements in an ultrasmall QW region enclosed in a nanocolumn revealed that narrow lines of individual excitons were localized on potential fluctuations attributed to 2-3-monolayer-high GaN clusters, which appear in QWs with an average thickness of 1 ML. The kinetics of luminescence with increasing temperature is determined via the change in the population of localized exciton states. At low temperatures, spin-forbidden dark excitons with lifetimes of ~40 ns predominate, while at temperatures elevated above 120 K, the overlying bright exciton states with much faster recombination dynamics determine the emission.

Increase in the Yield of X-rays and Terahertz Radiation from a Thin Foil Irradiated by Femtosecond Laser Pulses

Increase in the Yield of X-rays and Terahertz Radiation from a Thin Foil Irradiated by Femtosecond Laser Pulses

Significance of Plant Canopy Maintenance in Crop Yield

The yield of any crop depends on the capacity of a plant canopy to intercept and efficiently use the sunlight, which is dependent on canopy architecture of a plant viz., leaf size, shape and angle, number of leaves and branches, and a crop geometry viz., row orientation, row spacing, plant geometry, plant density, etc. The amount and distribution of leaf area in a crop canopy determine the way, by which, the photosynthetic active radiation is intercepted and consequently it influences the canopy photosynthesis and yield. The balance between the source and sink significantly contributes towards the higher accumulation of photosybthates Cropping geometry of a plant/crop affects the radiation use efficiency, intercepted photosynthetic active radiation (IPAR) and thereby the biological and economical yield of a crop. Optimum plant population stand and its density and a planting pattern with adequate spatial arrangement are important cultural factors that increase radiation interception and yield production.

Nanopolymer optically transparent structures, systems and devices

Search and analysis of results of theoretical and experimental studies on literature and patent sources in fields of optical and optical-electronic instrumentation are carried out. Current state and development trends of transparent polymer compositions containing nanoscale fillers, which open up new prospects for optical and optical-electronic instrumentation, are considered. Obtained data and recommendations on improvement and creation of new optically transparent nanocomposites are generalized, and can be used not only for connecting components of optical systems, but also for products in scintillation technology, lighting engineering, photovoltaics, and in many other fields of science and technology. Examples of some currently existing polymer and nanopolymer optical systems are considered, including an organosilicon composition for connecting optical elements, a plastic scintillator with nanostructured phosphors with improved time characteristics and light output values, an LED with multilayered scatterer with a variable index of refraction and an improved yield of radiation, optical compositions with a high refractive index on high transparency silicones for connection with optical elements in light-emitting devices or for lighting devices with a remote phosphor, as well as new materials and methods for dispersing nanoparticles. Given examples clearly show that complexity of the structures and micro dimensions of modern optical and optoelectronic products for their successful implementation and widespread adoption require new easy-to-use and not expensive optically transparent nanomaterials and technologies for their manufacture.

DETERMINING GAMMA SOURCE IN URANIUM MOLYBDENUM OF FUEL IN G.A SIWABESSY MULTI PURPOSE REACTOR

Nuclear fission reactions produce a lot of radionuclides that release energy, one of which is in the form of gamma radiation. Gamma radiation is produced by various types of radionuclides, and nuclear reactor fuel will produce different values of gamma intensity. Uranium Molybdenum (U7Mo-Al) is the type of nuclear fuel for future research reactors that possesses many advantages. For the application of molybdenum-based fuel, it is necessary to determine the resulting gamma radiation. The purpose is to determine the gamma radiation produced from molybdenum-based fuel with various densities. This study begins with the determination of the mass composition of the reactor component, calculations with ORIGEN2.1, and data output analysis. The U7Mo-Al density was varied, namely 2.96 gU/cm3, 3.85 gU/cm3, 4.44 gU/cm3, 5.43 gU/cm3, 6.91 gU/cm3, and 8.29 gU/cm3. The gamma radiation yield of U7Mo-Al is lower than that of uranium silicide (U3Si2) with the same density of 2.96 gU/cm3. The result will add to the justification for the superiority of U7Mo-Al compared to U3Si2/Al. For U7Mo-Al with densities of 3.85 gU/cm3, 4.44 gU/cm3, 5.43 gU/cm3, 6.91 gU/cm3, and 8.29 gU/cm3, the one that produced the lowest gamma radiation intensity is 3.85 gU/cm3 while the highest is 8.29 gU/cm3. This explains that the intensity of the gamma radiation produced is directly proportional to the fuel density. The low intensity of gamma radiation in molybdenum-based fuel can be used as a suggestion in shielding design to ensure the operational safety of reactors.

K-shell radiation and bright spot characteristics of high-energy-density Fe-Cr-Ni plasmas influenced by X-pinch load geometry

K-shell radiation is diagnostically advantageous for the study of high-energy-density plasmas. The current work investigates the influence of load geometry on K-shell x-rays in Z-pinch plasmas produced on the 1-MA Zebra generator. Stainless steel (Fe: 69%, Cr: 20%, Ni: 9%) X-pinch wire loads are fielded with an interwire angle of 31° (small-angle) or 62.5° (large-angle), respectively and studied using various x-ray diode, imaging, and spectroscopic diagnostics. The large-angle geometry produced large, individual x-ray-emitting bright spots (> 3 keV) at the wire cross-point averaging areas ≥ 1 mm2, with noteworthy soft x-ray (> 0.75 keV) bursts and radiation yields ≤ 14.6 kJ. The small-angle geometry produced multiple x-ray-emitting bright spots extending the pinch axis with smaller average sizes (≤ 0.5 mm2), consistent with stronger current, increased radiation yield (≥ 15.5 kJ), and notable hard x-ray (> 9 keV) bursts, which peak with largest cumulative bright spot size. Spectroscopic analysis is performed with non-LTE collisional-radiative modeling, indicating a cold, nonthermal plasma region radiating from neutral to Ne-like ions, a hot, thermal region radiating from Fe and Cr He- and Li-like ions, and an intermediate region radiating Kα satellites from Li-like to O-like ions. Modeling of the nonthermal and satellite features imply a fractional hot electron abundance ∼0.1% and ∼0.5% for large- and small-angle geometries, respectively. Relative intensity analysis is performed on Heα and Kα lines, revealing intensity ratios that deviate from the original wire composition. Optical depth estimates allude to optically thick, thermal K-shell plasmas with densities consistent with non-LTE modeling.

Cavity-enhanced zero-phonon emission from an ensemble of G centers in a silicon-on-insulator microring

We report the incorporation of an ensemble of G centers in silicon-on-insulator (SOI) microrings using ion implantation and conventional nanofabrication. The coupling between the emitters and the resonant modes of the microrings is studied using continuous-wave and time-resolved microphotoluminescence (PL) experiments. We observe the resonant modes of the microrings on PL spectra, on the wide spectral range that is covered by G center emission. By finely tuning the size of the microrings, we match their zero-phonon line at 1278 nm with a resonant mode of quality factor around 3000 and volume 7.2 (λ/n)3. The zero-phonon line intensity is enhanced by a factor of 5, both in continuous-wave and time-resolved measurements. This is attributed to the Purcell enhancement of zero-phonon spontaneous emission into the resonant mode and quantitatively understood considering the distribution of the G center dipoles. Despite the enhancement of the zero-phonon emission, we do not observe any sizeable decrease in the average lifetime of the G centers, which points at a low radiative yield (<10%). We reveal the detrimental impact of parasitic defects in heavily implanted silicon and discuss the perspectives for quantum electrodynamics experiments with individual color centers in lightly implanted SOI rings. Our results provide key information for the development of deterministic single-photon sources for integrated quantum photonics.

Influence of planting density and development stage on photosynthetically absorbed radiation, biomass and artemisinin yield of Artemisia annua L. ‘Apollon’

Influence of planting density and development stage on photosynthetically absorbed radiation, biomass and artemisinin yield of <i>Artemisia annua</i> L. ‘Apollon’

Simulation of the irradiance and yield calculation of bifacial PV systems in the USA and Germany by combining ray tracing and view factor model

Compared to conventional photovoltaic (PV), there are more influencing factors in bifacial photovoltaics to be considered to calculate incoming irradiance and energy yield. Accurate models to investigate the influences of the elevation, the albedo of the ground, the shading conditions between the PV rows and many other rear-side related factors are required. This paper combines the ray tracing (RT) and view factor (VF) models to calculate the irradiance with a subsequent electrical yield calculation using the one-diode model. To verify the results of the developed open-source simulation program BifacialSimu, accurate data from a plant in Golden, USA (single-axis tracked) and a commercially operated plant in Germany (fixed-tilt) are used. Through comparisons to the actual data, it can be concluded that a combination of RT and VF models seems to be valid for longer simulation periods with several months since the relative errors balance out. The RT-only simulation accurately reproduces the precise hourly radiation and electrical yield pattern. Still, a continuous positive deviation was found, which does not even out over long periods and is thus less accurate than the VF/RT combination. A simulation for a single month with RT can take several hours. Thus, the best simulation mode results according to user requirements.

Neutron Capture and Transmission Measurements of 54Fe at the RPI LINAC

54Fe radiative capture cross section and transmission measurements were conducted at the Rensselaer Polytechnic Institute (RPI) Gaerttner Linear Accelerator (LINAC) Center using an enriched 54Fe sample in the keV energy region. 54Fe is a constituent of natural iron, which is present in a large variety of nuclear grade materials. Therefore, it is important to have an accurate understanding of the cross sections of 54Fe, which can be measured experimentally. In the time-of-flight measurements conducted at the LINAC, an array of four C6D6 detectors surrounded the sample and radiative capture data were collected using a digital data acquisition system. Additionally, a Li-glass detector was used to collect transmission data using an analog data acquisition system. The radiative capture yield of the 54Fe measurements were normalized to saturated resonances observed in Au and Ta to obtain an absolute capture yield. The preliminary capture yield and preliminary transmission obtained can be compared to evaluations and existing experimental data. Some disagreements were observed in prominent d-wave capture resonances observed in 54Fe in the low-keV neutron energy region. Both sets of experimental data along with pre-existing datasets will greatly enhance RPI’s ability to perform resonance evaluation for 54Fe up to roughly 1 MeV.

The Yield of Cherenkov and Scintillation Radiation Generated by the 2.7 MeV Electron Beam in Plate PMMA Samples

In this paper, we have investigated characteristics of ultraviolet and visible radiation generated by the 2.7 MeV electrons. It is shown that the Cherenkov radiation (ChR) intensity predominates over scintillations including wavelength shifting and cathodoluminescence quenching in pure poly(methylmethacrylate) (PMMA) for such electron energy. To separate ChR and scintillations, we measured emission spectra and orientation dependence of the PMMA samples and compared with GEANT4 model taking into account only ChR mechanism.

Analysis of the relationship between yield in cereals and remotely sensed fAPAR in the framework of monitoring drought impacts in Europe

Abstract. This study focuses on the relationship between satellite-measured fraction of absorbed photosynthetically active radiation (fAPAR) and crop yield cereals in Europe. Different features of the relationship between annual yield and multiple time series of fAPAR, collected during different periods of the year, were investigated. The two key outcomes of the analysis are the identification of the period: (i) from March to October as the one having the highest positive correlation between fAPAR and yield and (ii) from February to May as the period characterised by most of the estimated negative correlation. While both periods align well with the commonly assumed dynamic of the growing season, spatial differences are also observed across Europe. On the one hand, the Mediterranean regions report the highest correlation values (r&gt;0.8) and the longest continuous periods with positive statistically significant results (up to 7 months), covering most of the growing season. On the other hand, the central European region is characterised by the most limited positive correlation values, with only 2 months or less showing statistically significant results. While marked differences in the overall capability to capture the full dynamic of yield are observed across Europe, fAPAR anomalies seem capable of discriminating low-yield years from the rest in most of the cases.

Helical CT versus intermittent CT fluoroscopic guidance for musculoskeletal needle biopsies: impact on radiation exposure, procedure time, diagnostic yield, and adverse events.

Image-guided percutaneous needle biopsies are essential in the workup of musculoskeletal (MSK) lesions. While helical CT (HCT) is well established, intermittent CT fluoroscopy (iCTF) is an increasingly used alternative. The purpose of this study is to establish whether differences in subject radiation exposure, procedure time, yield, or adverse events exist between HCT and iCTF guidance. This retrospective cohort study included consecutive MSK needle biopsies performed on a single-CT scanner over a 12-month period at a tertiary academic center. Subject demographics, radiation dose, and outcomes were abstracted from the medical record. Comparisons between the two cohorts were performed using Student's t-test for continuous data and using Fisher's exact test for categorical data and a two-tailed p value less than 0.05 was considered significant. Two hundred sixteen adults (115 (53.2%) females) with a mean age of 58.8 ± 18.4years, underwent 216 biopsies (109 (50.5%) HCT guided, 107 (49.5%) iCTF guided) between June 2017 and June 2018. Dose-length product (DLP) and volume CT dose index (CTDIvol) were significantly higher for the HCT cohort (HCT 698.9 ± 400.8 mGycm vs iCTF 312.8 ± 170.8 mGycm; p < 0.005 and HCT 19.1mGy ± 8.8 vs iCTF 6.9mGy ± 1.5, p < 0.001). No significant difference in diagnostic yield, procedure time, or adverse event rate was identified. For CT-guided MSK needle biopsies, iCTF decreases subject radiation dose compared to HCT without negatively affecting outcomes. iCTF should be strongly considered by radiologists performing MSK biopsies given the reduced patient radiation exposure.

Abstract 10257: Diagnostic Yield of Screening and Associated Factors for Transthyretin Cardiac Amyloidosis in Severe Aortic Stenosis

Introduction: Transthyretin cardiac amyloidosis (ATTR-CA) has been associated with severe aortic stenosis (AS), with some studies finding up to 20% of patients who undergo transcatheter aortic replacement (TAVR) have ATTR-CA. New therapies for ATTR-CA have brought significant interest in identifying patients at high risk for this disease. The purpose of this study was to prospectively evaluate the yield of universal testing for ATTR-CA in older patients with severe AS. Methods: All patients ≥ 70 years with severe, native, and degenerative AS seen in valve clinic for evaluation of TAVR were referred for technetium-99m pyrophosphate cardiac scintigraphy (PYP scan). Diagnosis was made via a combination of planar grade, heart to contralateral lung ratio, and single positron emission computed tomography/computed tomography. Patients with a positive PYP scan were referred for appropriate laboratory testing to rule out AL amyloidosis. Clinical and echocardiographic factors were correlated with the PYP result. Results: Over a 12-month period, 787 patients with severe AS were screened of which 543 met the inclusion criteria. Of these patients, 298 underwent a PYP scan with 232 not undergoing the scan for logistical and scheduling issues during the pandemic. The positivity rate was 4.3% (13/298). Patients with a positive PYP scan had higher rates of carpal tunnel syndrome (54% vs 14%, p &lt;0.001), abnormal global longitudinal strain (&gt; -18%) (100% vs 69%, p=0.044), low stroke volume index (≤35 ml/m 2 ) (92% vs 42%, p&lt;0.001), thick intraventricular septum ≥ 1.1 cm (100% vs 79%, p=0.07), and abnormal left ventricular mass index (83% vs 46%, p=0.010). Conclusions: The prevalence of ATTR-CA in severe AS is lower than cited in previous studies, likely due to the expanded indication for TAVR. A multiparametric diagnostic algorithm or risk score for ATTR-CA in AS could enhance the yield of screening, reduce cost and unnecessary radiation, and result in more rapid treatment of amyloidosis.

Excited-State Modification of Phenylimidazole-Based Cyclometalated Ir(III) Complexes through Secondary Bulky Aryl Substitution and Inductive Modification Enhances the Blue Emission Efficiency in Phosphorescent OLEDs

To elucidate the key parameters governing the emission properties of phenylimidazole (pim)-based Ir(III) emitters, including their electronic structure and the bulky aryl substitution effect, a series of pim-based iridium(III) complexes (Ir(Rpim-X)3, Rpim-X = 1-R-2-(X-phenyl)-1H-imidazole) bearing secondary pendants of increasing bulkiness [R = methyl (Me), phenyl (Ph), terphenyl (TPh), or 4-isopropyl terphenyl (ITPh)] and three different primary pim ligands (X = F, F2, and CN) were designed and synthesized. Based on photophysical and electrochemical analyses, it was found that the excited state properties are highly dependent on the bulkiness of the secondary substituent and the inductive nature of the primary pim ligand. The incorporation of bulky TPh/ITPh substituents in the second coordination sphere significantly enhanced the emission efficiencies in the solid state (ΦPL = 72.1-84.9%) compared to those of the methyl- or phenyl-substituted Ir(III) complexes (ΦPL = 30.4% for Ir(Mepim)3 and 63.7% for Ir(Phpim)3). Further modification of the secondary aryl substituent (Ir(TPhpim)3 → Ir(ITPhpim)3) through the incorporation of an isopropyl group and F substitution on the primary pim ligand (Ir(TPh/ITPhpim)3 → Ir(TPh/ITPhpim-F/F2)3) resulted in a slight decrease in the LUMO and a significant decrease in the HOMO energy levels, respectively; these energy level adjustments consequently amplified emission blue shifts, thereby enabling efficient blue electroluminescence in phosphorescent organic light-emitting diodes. Theoretical calculations revealed that the excited-state properties of pim-based Ir(III) complexes can be modulated by the nature of the peripheral substituent and the presence of an EWG substituent. Among the fabricated blue-emitting TPh/ITPh-substituted Ir(III) complexes, Ir(ITPhpim-F)3, Ir(TPhpim-F2)3, and Ir(ITPhpim-F2)3 were tested as blue-emitting dopants for blue phosphorescent OLEDs owing to their high solid radiative quantum yields (ΦPL = 75.9-84.9%). The Ir(ITPhpim-F)3-doped multilayer device displayed the best performance with a maximum external quantum efficiency of 21.0%, a maximum current efficiency of 43.6 cd/A, and CIE coordinates of 0.18 and 0.31.

A Geant4 Simulation on the Application of Multi-layer Graphene as a Detector Material in High-energy Physics

The excellent properties of graphene, such as its high thermal conductivity, high electrical conductivity, and high electron density, make it an ideal candidate as a detector material in high-energy physics applications. In this work, we demonstrate the feasibility of multi-layer graphene (MLG) as a detector material in a high-energy environment. The Geant4 software package was used to estimate the energy of the deposited electrons within various thicknesses of MLG, ranging from 3 to 20 nm. The efficiency of the MLG as a detector material was further analyzed from the scattering angle and the yield of the secondary particles produced from the electron interaction with the material. The incident electron’s kinetic energy used herein ranged between 30 keV and 1 GeV, at a particle fluence of 1×107 e/cm2. The results show that the deposited energy was relatively low for the interaction with 1 MeV electrons, and dramatically increased as the thickness increases beyond 15 nm. This result was further supported by the highest yield of gamma radiation recorded by the interaction with a kinetic energy larger than 1 MeV, for thickness larger than 15 nm. The results suggest that the MLG works best as a charged particle detector in low energy ranges, while for high energy ranges, a thickness over 15 nm is suggested. The findings demonstrate that a MLG with a thickness larger than 15 nm could potentially be used as a detector material in high-energy conditions.

Enhancement of red exciplex efficiency: A study of environmental heavy metal effect

By changing the coordinating metal in the electron accepting materials, we systematically studied the heavy metal effect on the performance of the exciplex with m-MTDATA as an electron donor. It is found that the environmental heavy metal effect of Lutetium could enhance the photoluminescence and electroluminescence intensity of red exciplex two times by decreasing its decay time and increasing its radiative efficiency. This shortened decay time could enhance the exciplex intensity by preventing it from phonon quenching effect under high temperature (300 K). As a result, high external quantum efficiency of 3% of pure red exciplex based OLED was achieved. While the paramagnetic metal Gadolinium might decrease the radiative quantum yields of both singlet and triplet exciplexes.

Sowing density rather than row spacing influences chia radiation use and yield

AbstractChia (Salvia hispanica L.) production worldwide has been encouraged due to its high essential fatty acid content that is effective for reducing cardiovascular affections. However, few studies have assessed the sowing density and row spacing to maximize chia grain yield (GY) and found controversial results. None of them reported effects on radiation interception and use efficiency that could help to clarify the controversial results. The objective of this study was to determine the effects of sowing density and row spacing on radiation interception and radiation use efficiency (RUE) of chia and their effects on chia growth and yield. Two field trials were conducted in Salta, Argentina, during 2017 and 2018, combining two factors: sowing density (5, 9, 13, 17, and 21 plants m−2) and row spacing (0.26 and 0.52 m). Photosynthetically active radiation (PAR) interception (PARi), RUE, biomass and GY components were measured. There was a clear effect of sowing density on the main growth and yield attributes, whereas there were no effects of row spacing. Sowing density had a greater impact on PARi than row spacing. Increasing sowing density increased PARi and RUE through earlier time of maximum PARi, accumulating more PAR producing more biomass and GY. Grain yield, which increased by 73 kg ha−1 per unit increase in plant density, was closely associated with biomass, grain number, and verticillaster number (VN), and negatively associated with 1,000‐grain weight (TGW). Summarizing sowing density rather than row spacing had a greater impact on growth and yield attributes of chia.

Nitrogen rates and plant density interactions enhance radiation interception, yield, and nitrogen use efficiencies of maize

The contributions of the different leaf layers to maize yields identified as middle leaf > lower leaf > upper leaf, where the vertical photosynthetically active radiation (PAR) in the canopy gradually decreases. We hypothesized that the allocation of more PAR and nitrogen (N) to the highest contributing leaves will would be beneficial for higher yields and N use efficiencies. The N application rate and plant density effectively regulated the canopy light and N distribution. We evaluated the interactive effects of N rate and plant density on the agronomic and ecophysiological characteristics of leaves at different orientations in a 2019/2020 field experiment. In this study, an N application rate of 180 kg ha–1 coupled with a plant density of 82,500 plants ha–1 achieved the highest yield and N recovery efficiency (NRE). In contrast to the traditional farming practices in northern China, the density was increased and N rate was reduced. Densification from 52,500 to 82,500 plants ha–1 increased the population leaf area index (LAI) by 37.1% and total photosynthetically active radiation (TPAR) by 29.2%; however, excessive density (from 82,500 to 97,500 plants ha–1) drastically reduced the proportion of TPAR by 28.0% in the lower leaves. With increased density, the leaf areas and angles of the upper leaves decreased much more than those of the other leaves, which allowed the middle and lower leaves to access more light, which manifested a smaller extinction coefficient for light (KL). A high yield (>1,000 kg ha–1) of maize could be achieved simultaneously with higher NRE; however, it was negatively correlated with internal N use efficiency (IEN). Higher N concentrations and lower total performance index (PItotal) in the lower leaves may be an important rationale for the reduction of IEN in high-yielding maize. Additionally, decreased N rate without yield reduction under higher densities was primarily attributed to the more uniform vertical N distribution [a smaller extinction coefficient for N (KN)]. These results suggest that the N fertilizer rate can be moderately reduced without a reduction in maize yield under high plant densities in northern China.