Function Of Flux Density Research Articles

Photosynthetic and Production of Urochloa ruziziensis Inoculated with Azospirillum brasilense under Drought

Aims: The objective of this study was to evaluate the photosynthetic activity and production of Urochloa ruziziensis when inoculated with Azospirillum brasilense in the presence and absence of drought.
 Study Design: Randomized block design and factorial 2x2.
 Methodology: The first factor was the presence or absence of seed inoculation with A. brasilense strains AbV5 + AbV6; the second factor was the presence or absence of drought. The variables evaluated were: relative water content (RWC), soil gravimetric moisture, net assimilation rate of CO2, response in function of active photon flux density, apparent quantum efficiency, light compensation point, absolute integrity of membrane, damage to membranes, dry mass aborted leaves, and total dry mass of aerial part.
 Results: Results demonstrate that plants maintained in drought presented a reduction in all evaluated variables. Under conditions of drought the use of A. brasilense promoted smaller variations in RWC, net assimilation rate of CO2, apparent quantum efficiency, light compensation point, absolute integrity of membrane, and damage to membranes; no variations were observed for dry mass, aborted leaves or total dry mass of aerial part.
 Conclusion: The inoculation of U. ruziziensis seeds with A. brasilense mitigates drought damage in plant physiology, but it does not mitigate leaf losses or plant productivity.

Leaf gas exchange variation under summer drought in Tunisian cork oak from geographically central and marginal populations

A global understanding of the ability of cork oak populations to cope with and adapt to summer drought stress is crucial for assessments of the future of cork oak forests as a major ecosystem in the Mediterranean. We examined the effect of summer drought on photosynthetic capacity in three Quercus suber (L.) populations that are native to different ecological conditions. Djebal Chahid (JCH) and Kef Errand (KER) originated from the driest sites and Feija (FEJ) from the wettest site. FEJ is the central area; however, JCH and KER are from geographically marginal sites of the species distribution range in Tunisia. The photosynthetic performance was monitored by measuring the leaf gas exchange and chlorophyll fluorescence parameters. The FEJ population leaves showed the lowest light-saturated rates of assimilation (Amax). However, the photosynthetic response curves as a function of photon flux density for leaves of different populations showed that the light compensation point was higher in FEJ compared to KER and JCH. The apparent quantum yield (Φ) was not significantly different between all the studied populations. The specific leaf area and chlorophyll content were similar in leaves of the studied populations, whilst assimilation seemed to be limited by stomatal factors. Our finding confirms previous studies showing a large population-level differentiation in cork oak with population from dry sites exhibiting a higher tolerance. This is useful to the forestry decision-makers to develop appropriate strategies to restore and protect forest ecosystems.

Experimental exploration of the upper measuring limit of pressure gauges for ITER by variation of instrumental parameters

Hot cathode ionization gauges are intended to be the only in-situ diagnostic for neutral gas pressures in the vacuum vessel of ITER. The development bases on the well established ASDEX pressure gauge. The upper measuring limit for ITER is required to be at least 20 Pa in hydrogen at a magnetic flux density of up to 8 T. The objective of the presented study is to find parameter and design settings that allow to satisfy this specification. At the same time, the sensitivity shall be high and only weakly dependent on the magnetic field strength. Gauge parameters, specifically the electron emission current, the electrode potentials and the transparency of the acceleration grid, were varied consecutively to assess their impact on the calibration characteristics. The ratio of ion to electron current as a function of pressure and magnetic flux density was obtained for each parameter set.A monotonic progression of the signal in dependence of the pressure was proven even up to 30 Pa. This was achieved by a low grid transparency and high electric field strength at the cathode. While the former leads to a lower sensitivity, which is unfavorable for measurements in the low pressure range, this can be compensated by a higher electron current.

The Solar Photospheric Continuum Brightness as a Function of Mean Magnetic Flux Density. I. The Role of the Magnetic Structure Size Distribution

Abstract Solar irradiance models indicate that irradiance variations are dominated by changes in the disk-coverage of magnetic structures, whose brightness is thought to be determined by their size and average magnetic flux density. Recent results suggest that the brightness of small-scale magnetic structures also depends on the mean magnetic flux of the extended region surrounding them due to reduced convective vigor. Low spatial resolution, however, may limit the ability to distinguish the role of magnetic structure size distributions from that of the mean magnetic flux. Using high-resolution 3D MHD simulations, we investigate the brightness of magnetic structures embedded in regions characterized by different mean magnetic flux. In agreement with previous results, we find reduced brightness with increasing mean magnetic flux when comparing the pixel-by-pixel continuum brightness versus magnetic field strength. Evaluating equivalently sized magnetic structures, however, we find no significant dependence of the magnetic structure brightness on the mean magnetic flux of the region in which they are embedded. Rather, we find that simulations with larger mean magnetic flux generate larger, and therefore darker, magnetic structures whose contributions result in an overall darkening of the region. The differences in magnetic structure size distributions alone can explain the reduced brightness of regions with larger mean magnetic flux. This implies that, for the range of mean magnetic flux of the simulations, convective suppression plays at most a secondary role in determining radiative output of magnetized regions. Quantifying the role of convective transport over a wider range of mean magnetic flux is the subject of the second paper in this series.

PALFA Single-pulse Pipeline: New Pulsars, Rotating Radio Transients, and a Candidate Fast Radio Burst

Abstract We present a new single-pulse pipeline for the PALFA survey to efficiently identify single radio pulses from pulsars, rotating radio transients (RRATs), and fast radio bursts (FRBs). We conducted a sensitivity analysis of this new pipeline in which many single pulses were injected into PALFA data and run through the pipeline. We find that for single pulse widths <5 ms, the sensitivity of our new pipeline is at most a factor of ∼2 less sensitive than theoretically predicted. For pulse widths >10 ms, as the DM decreases, the degradation in sensitivity gets worse and can increase up to a factor of ∼4.5. Using this pipeline, we have discovered seven pulsars and two RRATs, and identified three candidate RRATs and one candidate FRB. The confirmed pulsars and RRATs have DMs ranging from 133 to 386 pc cm−3 and flux densities ranging from 20 to 160 mJy. The pulsar periods range from 0.4 to 2.1 s. We report on candidate FRB 141113, which is likely astrophysical and extragalactic, having DM ≃ 400 pc cm−3, which is over the Galactic maximum along this line of sight by ∼100–200 pc cm−3. We consider implications for the FRB population and show via simulations that if FRB 141113 is real and extragalactic, the slope α of the distribution of integral source counts as a function of flux density (N(>S) ∝ S −α ) is 1.4 ± 0.5 (95% confidence range). However, this conclusion is dependent on assumptions that require verification.

The XXL Survey

We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30.4 square degrees, with rms <150 μJy beam−1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μJy beam−1, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μJy beam−1. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 ×rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey’s incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).

Leaf gas exchanges responses of atemoya scion grafted onto Annona rootstocks

We examined the hypothesis that leaf gas exchange of scion is affected by different rootstocks in wood plants. We investigated daily courses of gas exchange and photosynthetic potential using the CO2 assimilation rates as a function of photosynthetic photon flux density, and then assessed CO2 response curves in atemoya scion (Annona × atemoya Mabb.) grafted onto araticum-de-terra-fria [A. emarginata (Schltdl.) H. Rainer var. terra-fria]: ATF, araticum-mirim [A. emarginata (Schltdl.) H. Rainer var. mirim]: ATM, biriba [A. mucosa (Bail.) H. Rainer]: ATB, atemoya (autograft): ATA, and in ungrafted atemoya plants: CTR. Throughout the entire evaluation period, the net assimilation rate (Anet) and stomatal conductance (gs) of CTR plants remained practically constant, being lower than those of grafted plants between 08:00 a.m. and 12:00 a.m., regardless of the rootstock used. Moreover, ATM plants proved to be more efficient in keeping the stomata open, even during the hottest hours of the day, improving Anet and carboxylation use efficiency. However, this occurred at the lowest maximum carboxylation rate of ribulose-1,5-bisphosphate (Vcmax). Overall, ATF plants presented a low light saturation point and photosynthetic electron transport rates, though increased maximum quantum yield of photosynthesis was observed. Thus, we accept our hypothesis and conclude that grafting might affect the photosynthetic metabolism of the atemoya hybrid, regardless of the combination used, which promotes enhanced Anet and low Vcmax and light saturation points.

A newly developed media for magnetic abrasive finishing process: Material removal behavior and finishing performance

Magnetic abrasive finishing (MAF) is one of the most important final machining processes, and the performances of finishing media play an important role in the finishing effects and efficiency. In this study, a new magnetic finishing media with semi-solid state was presented and prepared, and finishing setup for the inner or outer rotary surface was developed. In order to determine the optimum angle between N pole and S pole, simulation was performed using ANSYS Maxwell 14.0. Mathematical modelling of the material removal ratio (MRR) was built as a function of magnetic pressure and velocity based on Archard wear model, and the developed model predicted the MRR as a function of magnetic flux density, mass ratio, rotational speed of magnetic poles, rotational speed of cam, and diameter of abrasive particles and ferromagnetic particles. The material removal coefficient of the predicted model was determined. The model was validated by experiment, and the relative error between the experiment value and the theoretical value was 4.51%. Finishing experiments of main parameters on surface roughness Ra and MRR were examined. Experimental results indicate that the percentage change % ΔRa in surface roughness Ra and the material removal amount increase with the increase of the rotational speed, the mesh number of the abrasive particles, and the mass ratio of base polymer, ferromagnetic phase and abrasive phase. For the 6061 aluminum alloy tube, the maximum improvement in surface roughness Ra is 96.67%, and the maximum MRR is 1.916 mg/s.

Dynamics of vortex line density and heat transfer processes in superfluid helium

Three dynamics equations for vortex line density are analyzed. It is shown that the Vinen equation gives the values of vortex tangle development time in the case of a constant counterflow more accurately than other alternative equations. Within the system of equations of superfluid turbulence hydrodynamics, obtained using a phenomenological approach, helium boiling times as a function of heat flux density are found, using alternative dynamics equations of vortex tangle density. Unlike the experiments in which different dependences of boiling time tboil on the heat flux density Q (tboil ∝ Qn, −4 ≤ n ≤ −2) are observed, in this case we get only a power-law dependence with an exponent of n = −4. We obtain a velocity distribution of the normal component along the channel, and the temperature dependence of the time near the heater. We conduct a comparison against the numerical and experimental results that were previously obtained in literature.

Experimental research of a two-phase nitrogen natural circulation loop

Two-phase heat and mass transfer in nitrogen has been experimentally investigated in a natural circulation loop. The experiments were realized in steady-state conditions near atmospheric pressure with a 10 mm inner diameter vertical copper tube, uniformly heated over roughly 1 m in length. The vapor and total mass flow rates and the wall temperature were measured as a function of the tube heat flux density. The investigated ranges-limits are 40 g/s, 25% and 30 kW/m2 for the total mass flow rate, the vapor quality and the heat flux density respectively. Transition from single phase natural convection to nucleate boiling flow is evidenced by wall temperature measurements at five different locations along the heated tube. The measurements are compared to the numerical computations of the total mass flow rate that is simulated by a set of conservation equations based on a simple separated flow model. The model catches most of the features of the mass flow rate evolution as a function of the heat flux density. In addition, the wall temperature measurements are used to determine the heat transfer coefficients that are compared with known correlations in both single phase natural convection and boiling flow. A majority of the data falls within ±20% of the predicted values given by the correlations.

An Improved Statistical Point-source Foreground Model for the Epoch of Reionization

Abstract We present a sophisticated statistical point-source foreground model for low-frequency radio Epoch of Reionization (EoR) experiments using the 21 cm neutral hydrogen emission line. Motivated by our understanding of the low-frequency radio sky, we enhance the realism of two model components compared with existing models: the source count distributions as a function of flux density and spatial position (source clustering), extending current formalisms for the foreground covariance of 2D power-spectral modes in 21 cm EoR experiments. The former we generalize to an arbitrarily broken power law, and the latter to an arbitrary isotropically correlated field. This paper presents expressions for the modified covariance under these extensions, and shows that for a more realistic source spatial distribution, extra covariance arises in the EoR window that was previously unaccounted for. Failure to include this contribution can yield bias in the final power-spectrum and under-estimate uncertainties, potentially leading to a false detection of signal. The extent of this effect is uncertain, owing to ignorance of physical model parameters, but we show that it is dependent on the relative abundance of faint sources, to the effect that our extension will become more important for future deep surveys. Finally, we show that under some parameter choices, ignoring source clustering can lead to false detections on large scales, due to both the induced bias and an artificial reduction in the estimated measurement uncertainty.

A novel phenomenological model for dynamic behavior of magnetorheological elastomers in tension–compression mode

Tension–compression operation in MR elastomers (MREs) offers both the most compact design and superior stiffness in many vertical load-bearing applications, such as MRE bearing isolators in bridges and buildings, suspension systems and engine mounts in cars, and vibration control equipment. It suffers, however, from lack of good computational models to predict device performance, and as a result shear-mode MREs are widely used in the industry, despite their low stiffness and load-bearing capacity. We start with a comprehensive review of modeling of MREs and their dynamic characteristics, showing previous studies have mostly focused on dynamic behavior of MREs in shear mode, though the MRE strength and MR effect are greatly decreased at high strain amplitudes, due to increasing distance between the magnetic particles. Moreover, the characteristic parameters of the current models assume either frequency, or strain, or magnetic field are constant; hence, new model parameters must be recalculated for new loading conditions. This is an experimentally time consuming and computationally expensive task, and no models capture the full dynamic behavior of the MREs at all loading conditions. In this study, we present an experimental setup to test MREs in a coupled tension–compression mode, as well as a novel phenomenological model which fully predicts the stress–strain material behavior as a function of magnetic flux density, loading frequency and strain. We use a training set of experiments to find the experimentally derived model parameters, from which can predict by interpolation the MRE behavior in a relatively large continuous range of frequency, strain and magnetic field. We also challenge the model to make extrapolating predictions and compare to additional experiments outside the training experimental data set with good agreement. Further development of this model would allow design and control of engineering structures equipped with tension–compression MREs and all the advantages they offer.

Canopy Net Photosynthesis Rate of a Mongolian Oak (<i>Quercus mongolica</i>) Forest Estimated by Field Experimental Data

The canopy net photosynthesis rate of Mongolian oak (Quercus mongolica) tree species that are dominant in East Asia and Korea is estimated with empirical models derived from field experimental data obtained from the Nam-San site in Seoul, Korea for the growing period from early May to late October in 2010. The empirical models include the attenuation function of photosynthetic photon flux density (PPFD) (r2 = 0.98-0.99, p r2 = 0.99, p level within canopy significantly varies diurnally and seasonally due to the seasonal variation of the total plant area index (TPAI = leaf area index + wood silhouette area index) and the light shielding effect of light path-length through the canopy in association with the variation of solar elevation angle. Consequently, a remarkable seasonal variation of the total canopy net photosynthesis rate of Q. mongolica forest stand is found for its growing period. The PPFD exceeding 1000 μmol m-2·s-1 is found to cause the decrease of net photosynthesis rate due to the thermal stress in the early (May) and late (September) growing period. During the whole growing season, the estimated total canopy net photosynthesis rate is found to be about 3.3 kg CO2 m-2.

Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

We investigate the 1/f noise properties of epitaxial graphene devices at low temperatures as a function of temperature, current and magnetic flux density. At low currents, an exponential decay of the 1/f noise power spectral density with increasing temperature is observed that indicates mesoscopic conductance fluctuations as the origin of 1/f noise at temperatures below 50 K. At higher currents, deviations from the typical quadratic current dependence and the exponential temperature dependence occur as a result of nonequilibrium conditions due to current heating. By applying the theory of Kubakaddi [S. S. Kubakaddi, Phys. Rev. B 79, 075417 (2009)], a model describing the 1/f noise power spectral density of nonequilibrium mesoscopic conductance fluctuations in epitaxial graphene is developed and used to determine the energy loss rate per carrier. In the regime of Shubnikov-de Haas oscillations a strong increase of 1/f noise is observed, which we attribute to an additional conductance fluctuation mechanism due to localized states in quantizing magnetic fields. When the device enters the regime of quantized Hall resistance, the 1/f noise vanishes. It reappears if the current is increased and the quantum Hall breakdown sets in.

Layerwise theory in modeling of magnetorheological laminated beams and identification of magnetorheological fluid

In recent years, structures integrated with magnetorheological (MR) fluid have been considered for their tunable dynamic characteristics. Shear modulus of MR layer in composite structure is dramatically lower than the elastic layers, leading to high shear deformation inside the MR layer, thus classical theories are not accurate enough to predict the dynamic behavior of such structures. In present study a layerwise displacement theory has been utilized to predict a more accurate deformation for MR-composite beam and equation of motions derived using finite element model (FEM). ASTM E756-98 was employed to evaluate the complex shear modulus of MR fluid. By experimental test a practical formulation for complex shear modulus of MR fluid was extracted. In this formulation shear modulus of MR fluid was presented as function of magnetic flux density and also driving frequency. Based on switched-stiffness vibration control concept a control algorithm was designed and effect of this control strategy on force and free vibration was examined.

Estimating light environment in forests with a new thresholding method for hemispherical photography

Light environment estimates derived from hemispherical photography are known to be affected by variations in sky illumination. During photo acquisition, rapid changes in sky illumination can occur and will result in changes in detected canopy gap size and frequency. Any resulting problems in image consistency will become more serious with increased time lags between setting the reference exposure and hemispherical photograph acquisition. We showed that if the camera exposure setting was kept constant during photo acquisition, the estimated diffuse transmittance would be greatly influenced by sky illumination change. We developed a new pixel thresholding method that calculated the optimal threshold value for the separation of sky and plant pixels as a function of the above-canopy photosynthetic photon flux density (PPFD). We tested the performance of our method for estimating transmittance against two established methods that assume exposure to be held constant to two stops higher than the reference exposure. Our method compensates for changes in sky illumination, producing a smaller pixel threshold value when sky illumination decreases and a larger pixel threshold value when photographs are taken under increased sky illumination. The new method achieved accurate and reproducible results, even in situations where under- or over-exposure was caused by changes in sky illumination during photo acquisition.

Effect of EDTA-assisted copper uptake on photosynthetic activity and biomass production of sweet Sorghum

Sweet sorghum (Sorghum bicolor L. Moench cv. Rona) is a widely grown sugar crop that is used for bioenergy production. Since sorghum shows increased sensitivity to nutrient deficiency, the objective of this study was to reach an appropriate Cu level in plant tissues using various concentrations of Cu and ethylenediaminetetraacetic acid (EDTA) in order to enhance the photosynthetic activity and biomass production of plants. Copper accumulation increased in the root and stem of plants irrigated for 12 weeks with 0.1 μM CuCl2 both in the presence and absence of 300 μM EDTA and as a consequence, the plant-available Cu concentration in the soil extracts was lower at harvest. Although the copper content of leaves slightly increased, the transport of Fe and Mn, the microelements participating in light reactions of photosynthesis was negatively affected. In spite of this, 0.1 μM CuCl2 alone and with 200 or 300 μM EDTA enhanced the maximal CO2 assimilation rate (Amax) as a function of photon flux density (PPFD) and increased soluble sugar content in all plant parts. The dry mass of plants especially that of stems increased very significantly after 0.1 μM CuCl2 + 300 μM EDTA treatment. These results show that non-toxic concentration of copper in combination with suitable concentration of EDTA can enhance photosynthesis, biomass production, sugar content and the total copper accumulation in the shoot of sweet sorghum plants.

Hybrid simplified spherical harmonics with diffusion equation for light propagation in tissues

Aiming at the limitations of the simplified spherical harmonics approximation (SPN) and diffusion equation (DE) in describing the light propagation in tissues, a hybrid simplified spherical harmonics with diffusion equation (HSDE) based diffuse light transport model is proposed. In the HSDE model, the living body is first segmented into several major organs, and then the organs are divided into high scattering tissues and other tissues. DE and SPN are employed to describe the light propagation in these two kinds of tissues respectively, which are finally coupled using the established boundary coupling condition. The HSDE model makes full use of the advantages of SPN and DE, and abandons their disadvantages, so that it can provide a perfect balance between accuracy and computation time. Using the finite element method, the HSDE is solved for light flux density map on body surface. The accuracy and efficiency of the HSDE are validated with both regular geometries and digital mouse model based simulations. Corresponding results reveal that a comparable accuracy and much less computation time are achieved compared with the SPN model as well as a much better accuracy compared with the DE one.

C ii] emission from galactic nuclei in the presence of X-rays

The luminosity of [C II] is used to probe the star formation rate in galaxies, but the correlation breaks down in some active galactic nuclei (AGNs). Models of the [C II] emission from galactic nuclei do not include the influence of X-rays on the carbon ionization balance, which may be a factor in reducing the [C II] luminosity. We calculate the [C II] luminosity in galactic nuclei under the influence of bright sources of X-rays. We solve the balance equation of the ionization states of carbon as a function of X-ray flux, electron, atomic hydrogen, and molecular hydrogen density. These are input to models of [CII] emission from the interstellar medium (ISM) in galactic nuclei. We also solve the distribution of the ionization states of oxygen and nitrogen in highly ionized regions. We find that the dense warm ionized medium (WIM) and dense photon dominated regions (PDRs) dominate the [C II] emission when no X-rays are present. The X-rays in galactic nuclei can affect strongly the C$^+$ abundance in the WIM converting some fraction to C$^{2+}$ and higher ionization states and thus reducing its [C II] luminosity. For an X-ray luminosity > 10$^{43}$ erg/s the [C II] luminosity can be suppressed by a factor of a few, and for very strong sources, >10$^{44}$ erg/s, such as found for many AGNs by an order of magnitude. Comparison of the model with extragalactic sources shows that the [C II] to far-infrared ratio declines for an X-ray luminosity >10$^{43}$ erg/s, in reasonable agreement with our model.

Angle-resolved photoelectron spectra of layers of finite thickness

The procedure for calculating X-ray photoelectron spectra in wide ranges of energy losses and viewing angles is developed. The spectra of semi-infinite samples and finite-thickness layers are studied. The angular and energy spectra are analyzed via a solution to the problem for the function of photoelectron emission flux density by means of the invariant embedding method. The energy spectrum is represented in the form of a number of inelastic collisions. The results of exact numerical solution of the problem of multiple photoelectron scattering in solids using the straight-line and small-angle approximations, experimental data, and results of Monte Carlo simulation are compared. Errors in calculations using the straight-line approximation and the advantages of models for describing the spectra in the framework of the small-angle approximation are revealed.