Spectral Photon Flux Research Articles

Estimation of time course in phytochrome photostationary state under artificial light for controlling plant growth.

A model to estimate the time course of a phytochrome photostationary state (PSS) under an arbitrary light environment was developed. It is the solution of differential equations that use conversion rates between active and inactive forms of previously reported phytochromes. The model estimated that 90% of the PSS changes were completed using approximately 3.4 mmol m-2 of integrated end-of-day far-red light irradiation, and 99% of the changes were completed with approximately 6.9 mmol m-2 irradiation. Although these values were affected by the spectral photon flux density of the far-red light. They were consistent with previous results that examined dose requirements of far-red irradiation. The rate at which the PSS changes approached equilibrium was maximized under a red light, followed by far-red, green, and blue light. This estimation method could be used to control phytochrome responses for horticulture via artificial lighting.

Incorporating the effect of the photon spectrum on biomass accumulation of lettuce using a dynamic growth model.

Cultivation studies in specialty crop optimization utilize models to estimate the fresh and dry mass yield. However, the spectral distribution and photon flux density affect plant photosynthetic rate and morphology, which is usually not incorporated in plant growth models. In this study, using data for indoor-grown lettuce (Lactuca sativa) cultivated under different light spectra, a mathematical model that incorporates these effects is presented. Different experimental cases are used to obtain a modified quantum use efficiency coefficient that varies with the spectral distribution. Several models for this coefficient are fitted using experimental data. Comparing the accuracy of these models, a simple first- or second-order linear model for light-use efficiency coefficient has about 6 to 8 percent uncertainty, while a fourth-order model has a 2 percent average error in prediction. In addition, normalizing overall spectral distribution leads to a more accurate prediction of the investigated parameter. A novel mathematical model based on normalized spectral irradiance integrated over wavelength for photosynthetically active radiation (PAR) wavebands and the far-red waveband is presented in this study. It accurately predicts lettuce dry mass grown indoors under different light spectra.

Photolysis of Gas-Phase Atmospherically Relevant Monoterpene-Derived Organic Nitrates.

Organic nitrates (ONs) can impact spatial distribution of reactive nitrogen species and ozone formation in the atmosphere. While photolysis of ONs is known to result in the release of NO2 back to the atmosphere, the photolysis rate constants and mechanisms of monoterpene-derived ONs (MT-ONs) have not been well constrained. We investigated the gas-phase photolysis of three synthetic ONs derived from α-pinene, β-pinene, and d-limonene through chamber experiments. The measured photolysis rate constants ranged from (0.55 ± 0.10) × 10-5 to (2.3 ± 0.80) × 10-5 s-1 under chamber black lights. When extrapolated to solar spectral photon flux at a solar zenith angle of 28.14° in summer, the photolysis rate constants were in the range of (4.1 ± 1.4) × 10-5 to (14 ± 6.7) × 10-5 s-1 (corresponding to lifetimes of 2.0 ± 0.96 to 6.8 ± 2.4 h) and (1.7 ± 0.60) × 10-5 to (8.3 ± 4.0) ×10-5 s-1 (3.3 ± 1.6 to 17 ± 6.0 h lifetimes) by using wavelength-dependent and average quantum yields, respectively. Photolysis mechanisms were proposed based on major products detected during photolysis. A zero-dimensional box model was further employed to simulate the photolysis of α-pinene-derived ON under ambient conditions. We found that more than 99% of α-pinene-derived ON can be converted to inorganic nitrogen within 12 h of irradiation and ozone was formed correspondingly. Together, these findings show that photolysis is an important atmospheric sink for MT-ONs and highlight their role in NOx recycling and ozone chemistry.

Alternation of temporally overlapped red and blue light under continuous irradiation affected yield, antioxidant capacity and nutritional quality of purple-leaf lettuce

The responses of yield, nutritional quality and antioxidant capacity of hydroponic purple-lettuce were investigated in a plant factory to different alternations of temporally overlapped red (R) and blue (B) light under continuous irradiation in which spectral photon flux density distribution changed with various combinations of R and B LEDs on a 24-h cycle. Two constant simultaneous rend and bleu (R-B) light treatments including one normal photoperiod (RB, 16/8 h, 225 μmol·m−2·s−1) and one continuous light (RB’, 24/0 h, 150 μmol·m−2·s−1) as well as three alternating temporally overlapped light treatments (B to R-B and then R, each part lasts the same time) with alternating frequencies of one time (T1), two times (T2) and four times (T4) respectively in 24 h were set up with the same daily light integral (DLI). The lettuce plants were exposed to the irradiation patterns for 14 days. In all treatments, plants received the same quantum number of red or blue light and the same daily light integral (12.96 μmol·m−2). In comparison with normal photoperiod (RB), the results showed that lettuce plants gained greater shoot fresh and dry weight under RB’ and T1 both on the 7 and 14 days after treatment, which depended on leaf area and biomass allocation. Among alternating light treatments, the shoot fresh weight of lettuce decreased with the increase of alternating frequencies. Lettuce plants under alternating temporally overlapped treatments had significantly higher MDA, H2O2 and O2− contents as well as higher SOD and CAT activities than that under RB and RB’. Alternating light treatments also induced phenols accumulation, and particularly lettuce under T2 had significantly higher anthocyanin, flavonoid and total phenol contents than RB. However, prolongation of light period under the same DLI condition might promote nitrate accumulation in lettuce while had no positive effects on starch and soluble sugar contents. Therefore, alternating temporally overlapped red and blue light under continuous irradiation could improve the antioxidant capacity of lettuce to a certain extent, and the responses of lettuce antioxidant system to alternating light exposure might depend on the duration and alternating frequency of two monochromatic light qualities.

Cultivation of cos lettuce using blue LED and quantum dot wavelength conversion sheets

The aims of this study were to cultivate cos lettuce (Lactuca sativa L. cv. Cos Lettuce) using quantum dot (QD) sheets for wave conversion and to clarify the advantages and disadvantages of this technique for plant cultivation with artificial lighting. Blue LED light was wavelength-converted to green (G-QD) or red (R-QD) light by QD sheets and used for cultivating cos lettuce. Then, lighting with spectral photon flux density distributions similar to those of G-QD and R-QD was designed using green or red LED and blue LED (G-LED and R-LED), respectively, and used for cultivating cos lettuce. Plant growth at 14 days after treatment revealed that the shoot fresh weight was greater under G-QD compared with G-LED, perhaps because the amount of integrated light reception was greater in G-QD owing to the difference in the photosynthetic photon flux density's spatial distribution. Plants showed similar growth levels and morphologies under R-QD and R-LED lights. Plant growth is affected by the light environment, such as spectral photon flux density distributions and its vector field, regardless of the light source. However, the prototype QD sheets used in the present study had low conversion efficiencies and wide directivity angles. If QD products are developed that utilize the advantages of high monochromaticity and long life for plant cultivation at low costs, then they may become widely used.

Excitation Properties of Photopigments and Their Possible Dependence on the Host Star

Abstract Photosynthesis is a plausible pathway for the sustenance of a substantial biosphere on an exoplanet. In fact, it is also anticipated to create distinctive biosignatures detectable by next-generation telescopes. In this work, we explore the excitation features of photopigments that harvest electromagnetic radiation by constructing a simple quantum-mechanical model. Our analysis suggests that the primary Earth-based photopigments for photosynthesis may not function efficiently at wavelengths >1.1 μm. In the context of (hypothetical) extrasolar photopigments, we calculate the potential number of conjugated π-electrons (N ⋆) in the relevant molecules, which can participate in the absorption of photons. By hypothesizing that the absorption maxima of photopigments are close to the peak spectral photon flux of the host star, we utilize the model to estimate N ⋆. As per our formalism, N ⋆ is modulated by the stellar temperature, and is conceivably higher (lower) for planets orbiting stars cooler (hotter) than the Sun; exoplanets around late-type M-dwarfs might require an N ⋆ twice that of the Earth. We conclude the analysis with a brief exposition of how our model could be empirically tested by future observations.

Study on X-ray Emission Using Ultrashort Pulsed Lasers in Materials Processing.

The interaction of ultrashort pulsed laser radiation with intensities of 1013 W cm−2 and above with materials often results in an unexpected high X-ray photon flux. It has been shown so far, on the one hand, that X-ray photon emissions increase proportionally with higher laser power and the accumulated X-ray dose rates can cause serious health risks for the laser operators. On the other hand, there is clear evidence that little variations of the operational conditions can considerably affect the spectral X-ray photon flux and X-ray emissions dose. In order to enhance the knowledge in this field, four ultrashort pulse laser systems for providing different complementary beam characteristics were employed in this study on laser-induced X-ray emissions, including peak intensities between 8 × 1012 W∙cm−2 < I0 < 5.2 × 1016 W∙cm−2, up to 72.2 W average laser power as well as burst/bi-burst processing mode. By the example of AISI 304 stainless steel, it was verified that X-ray emission dose rates as high as > 45 mSv h−1 can be produced when low-intensity ultrashort pulses irradiate at a small 1 µm intra-line pulse distance during laser beam scanning and megahertz pulse repetition frequencies. For burst and bi-burst pulses, the second intra-burst pulse was found to significantly enhance the X-ray emission potentially induced by laser pulse and plasma interaction.

Blue Light Monochromatic Irradiation for 12 Hours in Lighting Pattern with Combinations of Blue and Red Light Elongates Young Cos Lettuce Leaves and Promotes Growth under High Daily Light Integral

Cos lettuce was grown under different spectral photon flux density distribution (SPFD) change patterns with blue- and/or red light-emitting diode (LED) irradiation with a 24-hour cycle. Twelve treatments were designed with a combination of four relative SPFD (RSPFD) change patterns and three photosynthetic photon flux density (PPFD) levels. The RSPFD change patterns were as follows: BR/BR, simultaneous blue- and red-light irradiation (BR) for 24 h; R/BR, red-light monochromatic irradiation (R) for 12 h followed by 12 hours of BR; B/BR, blue-light monochromatic irradiation (B) for 12 hours followed by 12 hours of BR; and B/R, 12 hours of B followed by 12 hours of R. Each RSPFD change pattern was conducted at three daily average photosynthetic photon flux densities (PPFDave) of 50, 100, and 200 µmol·m−2·s−1. The RSPFD change patterns that included B (B/BR and B/R) resulted in elongated leaves. A low ratio of active phytochrome to total phytochrome under B was considered the reason for leaf elongation. Shoot dry weight was significantly greater under the RSPFD change patterns that included B when the PPFDave was 200 µmol·m−2·s−1. The leaf elongation caused by B would have increased the amount of light received and thereby promoted growth. However, excessive leaf elongation caused the plants to fall, and growth was not promoted under the RSPFD change patterns that included B when the PPFDave was 50 µmol·m−2·s−1. Thus, 12-hour B promoted growth under conditions in which leaf elongation leads to increases in the amount of light received.

Effects of Artificially Reproduced Fluctuations in Sunlight Spectral Distribution on the Net Photosynthetic Rate of Cucumber Leaves.

The effects of photosynthetic photon flux density (PPFD) fluctuations in sunlight have already been investigated; however, the spectral photon flux density distribution (SPD) has hardly been considered. Here, sunlight SPD fluctuations recorded for 200 min in October in Tokyo, Japan were artificially reproduced using an LED-artificial sunlight source system. The net photosynthetic rate (Pn) of cucumber leaves under reproduced sunlight was measured and compared with the Pn estimated from a steady-state PPFD–Pn curve for the same leaves. The measured and estimated Pn agreed except when the PPFD was low, where the measured Pn was lower than the estimated Pn. The ratio of measured Pn to estimated Pn was 0.94–0.95 for PPFD ranges of 300–700 μmol m–2 s–1, while the value was 0.98–0.99 for 900–1,300 μmol m–2 s–1, and the overall ratio was 0.97. This 3% reduction in the measured Pn compared with the Pn estimated from a steady-state PPFD–Pn curve was significantly smaller than the approximately 20–30% reduction reported in previous experimental and simulation studies. This result suggests that the loss of integral net photosynthetic gain under fluctuating sunlight can vary among days with different fluctuation patterns or may be non-significant when fluctuations in both PPFD and relative SPD of sunlight are taken into consideration.

Time-varying Photosynthetic Photon Flux Density and Relative Spectral Photon Flux Density Distribution to Improve Plant Growth and Morphology in Plant Factories with Artificial Lighting

In contrast to fluorescent lamps and high-power sodium lamps, the use of light-emitting diode (LED) lamps enables the control of not only photosynthetic photon flux density (PPFD) at the plant level, but also the relative spectral photon flux density distribution (RSPD) of light because of the variety, even at different times of day, of producible light emitted by LEDs of different types. Effects of the spectral photon flux density on plant growth and morphology have been investigated using several types of LEDs and plant species. However, few studies on lighting methods with time-varying PPFD or RSPD have been published to date. In this paper, we summarize the effects of time-varying PPFD on the net photosynthetic rate (Pn) and those of time-varying RSPD on plant growth and morphology. Detailed modeling studies have been conducted on the reactions of the photosynthetic pathway under time-varying PPFD at a cycle of milliseconds to seconds. The results of these modeling studies and actual measurements of Pn under pulsed light clearly indicate that pulsed light is not advantageous to improve Pn. Although the integrated PPFD of blue and red light was unchanged, the growth of leaf lettuce was promoted by asynchronous irradiation with blue light and red light compared with growth under simultaneous irradiation. We think that blue-light monochromatic irradiation promotes leaf elongation through leaf expansion as a primary factor in the enhancement of plant growth. In addition, changes in leaf photosynthetic capacity caused by blue-light monochromatic irradiation may be involved in plant growth promotion. An increasing number of studies have investigated the effects of time-varying RSPD on plants. However, the mechanisms underlying these effects remain to be elucidated.

Micropropagation of sea grape (Coccoloba uvifera (L.) L.)

A method for micropropagation of Coccoloba uvifera (L.) L. has been developed through bud proliferation from surface-sterilized nodal explants collected from a 9 yr old mature tree. Ninety six percent of the explants exhibited bud development on agar-gelled Murashige and Skoog's (MS) medium supplemented with 3.0 mg L−1 6-benzylaminopurine (BAP) if incubated at 26 ± 2 °C, under 40–50 µmol m−2s−1 spectral photon flux density (SPFD) light intensity for 16/8 h light/dark photoperiod and 55–60% relative humidity. The cloned buds multiplied (12 ± 1.30 shoots per inoculum), and grew on MS medium + 1.0 mg L−1 BAP + 0.5 mg L−1 of α-Naphthalene acetic acid (NAA) and additives, 50 mg L−1 ascorbic acid, 25 mg L−1 each of adenine sulphate, citric acid and arginine. Higher concentrations of auxins in the culture medium induced callus formation. The additives improved quality of shoots as these prevented deformation of shoots. The shoots rooted (7.2 roots per shoot) on half-strength MS medium with 2.5 mg L−1 NAA. Ex vitro rooting was achieved by treating the basal parts of the in vitro shoots with 400 mg L−1 NAA (14.6 roots per shoot) and subsequent planting in pots filled with 1:1:1 mixture of soilrite® (soil conditioning mixture), cocopeat and garden soil. The cloned plantlets were acclimatized in greenhouse; 93.8% of these were survived. This tissue culture method can be applied for large scale production and sustainable conservation of C. uvifera, a vulnerable species for agroforestry of the coastal regions for windbreak and soil reclamations.

How does a collapsing star look?

Time evolution of an optical image of a pressureless star under gravitational collapse is studied in the geometric optics approximation. The star surface is assumed to emit radiation obeying Lambert's cosine law but with an arbitrary spectral intensity in the comoving frame. We develop a formalism for predicting observable quantities by photon counting and by radiometry, in particular, spectral photon flux and spectral radiant flux. Then, this method is applied to the two cases: One is monochromatic radiation, and the other is blackbody radiation. The two kinds of spectral flux are calculated numerically for each case. It is reconfirmed that the redshift factor remains finite and the star becomes gradually invisible due to decay of the photon flux. We also develop an approximate method to present analytic formulas that describe the late time behavior. A possible connection of our study to observation of high-energy neutrinos is briefly discussed.

Why is chlorophyll b only used in light-harvesting systems?

Chlorophylls (Chl) are important pigments in plants that are used to absorb photons and release electrons. There are several types of Chls but terrestrial plants only possess two of these: Chls a and b. The two pigments form light-harvesting Chl a/b-binding protein complexes (LHC), which absorb most of the light. The peak wavelengths of the absorption spectra of Chls a and b differ by c. 20 nm, and the ratio between them (the a/b ratio) is an important determinant of the light absorption efficiency of photosynthesis (i.e., the antenna size). Here, we investigated why Chl b is used in LHCs rather than other light-absorbing pigments that can be used for photosynthesis by considering the solar radiation spectrum under field conditions. We found that direct and diffuse solar radiation (PARdir and PARdiff, respectively) have different spectral distributions, showing maximum spectral photon flux densities (SPFD) at c. 680 and 460 nm, respectively, during the daytime. The spectral absorbance spectra of Chls a and b functioned complementary to each other, and the absorbance peaks of Chl b were nested within those of Chl a. The absorption peak in the short wavelength region of Chl b in the proteinaceous environment occurred at c. 460 nm, making it suitable for absorbing the PARdiff, but not suitable for avoiding the high spectral irradiance (SIR) waveband of PARdir. In contrast, Chl a effectively avoided the high SPFD and/or high SIR waveband. The absorption spectra of photosynthetic complexes were negatively correlated with SPFD spectra, but LHCs with low a/b ratios were more positively correlated with SIR spectra. These findings indicate that the spectra of the photosynthetic pigments and constructed photosystems and antenna proteins significantly align with the terrestrial solar spectra to allow the safe and efficient use of solar radiation.

The absolutely characterized nitrogen vacancy center-based single-photon source – measurement uncertainty of photon flux and angular emission properties

Recently, a single-photon source based on the nitrogen vacancy center in a nanodiamond with a traceable spectral photon flux was realized [1]. In this article, we report on the determination of the measurement uncertainty of the spectral photon flux (about 4 %) and discuss its different components. Furthermore, the angular distribution of the emission of an NV center in a nanodiamond located in the vicinity of a dielectric boundary is calculated based on the model of Lukosz and Kunz. The agreement between the angular distribution calculation and the first-ever measurement of the angle-dependent emission in nanodiamond NV centers is satisfactory.

Experimental realization of an absolute single-photon source based on a single nitrogen vacancy center in a nanodiamond

We report on the experimental realization of an absolute single-photon source based on a single nitrogen vacancy (NV) center in a nanodiamond at room temperature and on the calculation of its absolute spectral photon flux from experimental data. The single-photon source was calibrated with respect to its photon flux and its spectral photon rate density. The photon flux was measured with a low-noise silicon photodiode traceable to the primary standard for optical flux, taking into account the absolute spectral power distribution using a calibrated spectroradiometer. The optical radiant flux is adjustable from 55 fW, which is almost the lowest detection limit for the silicon photodiode, and 75 fW, which is the saturation power of the NV center. These fluxes correspond to total photon flux rates between 190,000 photons per second and 260,000 photons per second, respectively. The single-photon emission purity is indicated by a g(2)(0) value, which is between 0.10 and 0.23, depending on the excitation power. To our knowledge, this is the first single-photon source absolutely calibrated with respect to its absolute optical radiant flux and spectral power distribution, traceable to the corresponding national standards via an unbroken traceability chain. The prospects for its application, e.g., for the detection efficiency calibration of single-photon detectors as well as for use as a standard photon source in the low photon flux regime, are promising.

Interaction between the spectral photon flux density distributions of light during growth and for measurements in net photosynthetic rates of cucumber leaves.

The net photosynthetic rate of a leaf becomes acclimated to the plant's environment during growth. These rates are often measured, evaluated and compared among leaves of plants grown under different light conditions. In this study, we compared net photosynthetic rates of cucumber leaves grown under white light-emitting diode (LED) light without and with supplemental far-red (FR) LED light (W- and WFR-leaves, respectively) under three different measuring light (ML) conditions: their respective growth light (GL), artificial sunlight (AS) and blue and red (BR) light. The difference in the measured photosynthetic rates between W- and WFR-leaves was greater under BR than under GL and AS. In other words, an interaction between supplemental FR light during growth and the spectral photon flux density distribution (SPD) of ML affected the measured net photosynthetic rates. We showed that the comparison and evaluation of leaf photosynthetic rates and characteristics can be biased depending on the SPD of ML, especially for plants grown under different photon flux densities in the FR waveband. We also investigated the mechanism of the interaction. We confirmed that the distribution of excitation energy between the two photosystems (PSs) changed in response to the SPD of GL, and that this change resulted in the interaction, as suggested in previous reports. However, changes in PS stoichiometry could not completely explain the adjustment in excitation energy distribution observed in this study, suggesting that other mechanisms may be involved in the interaction.

Effects of temporally shifted irradiation of blue and red LED light on cos lettuce growth and morphology

This study examined the growth and morphology of cos lettuce (Lactuca sativa L.) to ascertain the effects of irradiation patterns with combinations of blue and red LED light, with spectral photon flux density changing with a period of 24h. In experiment 1, plants were grown under irradiation patterns in which plants were irradiated with blue and red LED lights at a PPFD of 90μmolm−2s−1 for 14h per day respectively. The red LED light irradiation starting time was simultaneous to or delayed 1, 4, or 7h from the blue LED light irradiation starting time. Results showed that the shoot fresh weight of plants grown under irradiation patterns with red LED light irradiation being delayed 4 or 7h from blue LED light irradiation was significantly greater than that under irradiation patterns with blue and red LED light irradiation starting simultaneously. This result showed that the growth of plants can be promoted merely by temporally shifting the irradiation hours of blue and red LED lights. We then conducted experiments to assess the mechanism of the observed growth-promoting effect from viewpoints of the diurnal PPFD change and duration of blue and red light monochromatic irradiation. The results of these experiments revealed that the diurnal PPFD change contributed to the growth-promoting effect and that blue and/or red light monochromatic irradiation increased the total leaf area of plants.

On the nature of the photocurrent in secondary-emission multipliers of atomic-beam tubes

The physical cause for origination of the photocurrent in secondary-emission multipliers (SEMs) after long-term studies in the operation mode used for stabilization of parameters of atomic-beam tubes is considered. A general expression for the spectral photon flux penetrating through the channel connecting the ionizer with the SEM due to reflections in the channel and impinging on the surface of the first dynode of the SEM is obtained. Estimates of three versions of simplification of the general expression for the spectral photon flux are performed for several δ, i.e., average values of fine irregularities (in μm) characterizing the surface roughness of the channel, including a specified class of the channel treatment quality, and radiation angles of incidence on the channel surface θ. The expression that is the closest to correct determination of the illumination function of the surface of the first SEM dynode by a absolute black body source, which is described by the Wien equation at radiation wavelengths λ ≤ 2 μm, is determined.

Sunlight multiband Photon Flux Density detection based on PFD calculation model.

The sunlight provides essential light and temperature for photosynthesis in protected cultivation. Sunlight is one of the important plant living environment factors in facility agriculture. Most of the existing light detecting equipment are used to detect the whole band of Photosynthetic Available Radiatio (PAR), which is unable to meet the demand of modern photosynthesis research. In order to solve the problem, a function model between single-band spectral Photon Flux Density (PFD) and solar altitude was established through experiments. Based on the model, a sunlight multiband PFD detecting device was designed, which was using a PAR sensor as the detecting node and microcontroller as the core part. This device can detect the PFD of different bands in PAR by using a single sensor. Meanwhile, detecting band can be set by using keyboard according to the characteristic of spectrum absorption of different plants. The secure digital memory card (SD card) was used in the device to store data. Results of the field test showed that determination coefficients of the device testing red and blue PFD with standard value were 0.986 and 0.993 respectively. The device with little relative error and high reliability could be applied in facility light detecting. Keywords: photosynthetic available radiatio (PAR), photon flux density (PFD), solar altitude, detection, model DOI: 10.3965/j.ijabe.20150802.1293

The Relationship between the Power-Law Indices of the Temporal Properties on Energy and the Spectral Lag and Photon Flux of Gamma-Ray Burst Pulses

Abstract Previous studies have shown that the dependence of the pulse temporal properties (pulse width, pulse rise width, pulse decay width, and pulse peak time) on energy is a power-law function. In this work we demonstrate that the power-law indices of the pulse width, pulse rise width, pulse decay width, and pulse peak time on energy are correlated with the spectral lag and the relative spectral lag, $ \bigtriangleup t_{31}/w_{3}$ (where $ \bigtriangleup t_{31}$ and $ w_{3}$ are the spectral lag between BATSE channels 1 and 3 and the pulse width of BATSE channel 3, respectively), using a sample including 102 well-separated long-duration gamma-ray burst pulses. In addition, the correlations of the power-law indices with the relative spectral lags are much more tighter than those with the spectral lags. We further find that the power-law indices are also correlated with the pulse photon flux. The possible origins of these correlations are also discussed. We argue that the kinematic effect can explain the correlated properties.