Values Of Decay Constants Research Articles

Long-term impact of fertilizers on soil organic carbon pools and sequestration rates in maize–wheat–cowpea cropping system

We assessed the impact of long-term manuring and fertilization on changes in different SOC fractions over ten years period (1994–2003) in a Typic Haplustept under intensive cropping with maize ( Zea mays L.) — wheat ( Triticum aestivum L.) — cowpea ( Vigna unguiculata) in semi-arid, sub-tropical India. The application of graded doses of NPK from 50% (130 kg N, 35 kg P and 41.5 kg K ha − 1 ) to 150% (390 kg N, 105 kg P and 124 kg K ha − 1 ) in the cropping system significantly enhanced SOC, particulate organic C (POC) and KMnO 4 oxidizable C (KMnO 4–C) fractions in soil. The increase in these C fractions was greater when farmyard manure (FYM) was applied conjointly with 100% NPK (260 kg N, 70 kg P and 83 kg K ha − 1 ). This treatment showed highest amount of SOC (58.3 Mg C ha − 1 in 1994 and 72.1 Mg C ha − 1 in 2003), POC (5.30 Mg C ha − 1 in 1994 and 6.33 Mg C ha − 1 in 2003) and KMnO 4-C (10.05 Mg C ha − 1 in 1994 and 11.2 Mg C ha − 1 in 2003) in 0–45 cm soil depth. The C sequestration rate in SOC calculated over ten year period (1994–2003) was highest with 100% NPK + FYM (997 kg C ha − 1 yr − 1 ) followed by the 150% NPK (553 kg C ha − 1 yr − 1 ). It was estimated that 17.1 to 34.0% of the gross C input over ten year period contributed towards the increase in SOC content, while C sequestration efficiency (CSE) in POC (varied between 1.28 and 2.58%) was lower than KMnO 4-C (varied between 1.42 and 3.72%). The CSE was highest in 150% NPK treatment, while 100% NPK + FYM showed the lowest CSE. By applying the values of humification constant ( h) and decay constant ( k) in Jenkinson's equation, it is possible to predict SOC level in the year 2003 and the C inputs required to maintain the SOC level in the year 1994 ( A E) were calculated from Jenkinson's equation. The low k value in native SOC was responsible for lower requirements of C input required to maintain SOC in equilibrium. Thus increase in SOC concentration under long-term maize–wheat–cowpea cropping was due to the fact that annual C input by the system was higher than A E. In semi-arid sub-tropical India, continuous adoption of 100% NPK + FYM treatment in maize–wheat–cowpea cropping system might sequester 1.83 Tg C yr − 1 which corresponds to about 1% of the fossil fuel emissions by India.

Litter Decomposition in Temperate Peatland Ecosystems: The Effect of Substrate and Site

The large accumulation of organic matter in peatlands is primarily caused by slow rates of litter decomposition. We determined rates of decomposition of major peat-forming litters of vascular plants and mosses at five sites: a poor fen in New Hampshire and a bog hummock, a poor fen, a beaver pond margin and a beaver pond in Ontario. We used the litterbag technique, retrieving triplicate litterbags six or seven times over 3‐5 years, and found that simple exponential decay and continuous-quality non-linear regression models could adequately characterize the decomposition in most cases. Within each site, the rate of decomposition at the surface was generally Typha latifolia leaves = Chamaedaphne calyculata leaves = Carex leaves > Chamaedaphne calyculata stems > hummock Sphagnum = lawn/hollow Sphagnum, with exponential decay constant (k) values generally ranging from 0.05 to 0.37 and continuous-quality model initial quality (q0) values ranging from 1.0 (arbitrarily set for Typha leaves) to 0.7 (Sphagnum). In general, surface decay rates were slowest at the bog hummock site, which had the lowest water table, and in the beaver pond, which was inundated, and fastest at the fens. The continuous-quality model site decomposition parameter (u0) ranged from 0.80 to 0.17. Analysis of original litter samples for carbon, nitrogen and proximate fractions revealed a relatively poor explanation of decomposition rates, as defined by k and q0, compared to most well-drained ecosystems. Three litters, roots of sedge and a shrub and Typha leaves, were placed at depths of 10, 30 and 60 cm at the sites. Decomposition rates decreased with depth at each site, with k means of 0.15, 0.08 and 0.05 y )1 at 10, 30 and 60 cm, respectively, and u0 of 0.25, 0.13 and 0.07. These differences are primarily related to the position of the water table at each site and to a lesser extent the cooler temperatures in the lower layers of the peat. The distinction between bog and fen was less important than the position of the water table. These results show that we can characterize decomposition rates of surface litter in northern peatlands, but given the large primary productivity below-ground in these ecosystems, and the differential rates of decomposition with depth, subsurface input and decomposition of organic matter is an important and relatively uncertain attribute.

Light-cone distribution amplitudes of axial-vector mesons

We have presented a detailed study of twist-2 and twist-3 light-cone distribution amplitudes of 1 P 1 3 and 1 P 1 1 axial-vector mesons, based on QCD conformal partial wave expansion. Applying equations of motion, the twist-three two-parton light-cone distribution amplitudes can be expressed in terms of leading-twist and twist-three three-parton light-cone distribution amplitudes. The relevant G-parity invariant and violating parameters, containing the corrections due to the SU ( 3 ) breaking effects, are evaluated from the QCD sum rule method. The results for axial-vector decay constants of 1 P 1 3 states are presented. The values of tensor decay constants and Gegenbauer moments of the leading twist distribution amplitudes for 1 P 1 1 states are updated. Using Gell-Mann–Okubo mass formula, the mixing angle for the f 8 and f 1 of 1 P 1 3 states is θ P 1 3 ∼ 38 ° , and that for h 8 and h 1 of 1 P 1 1 states is θ P 1 1 ∼ 10 ° . The detailed properties for physical states f 1 ( 1285 ) , f 1 ( 1420 ) , h 1 ( 1170 ) , and h 1 ( 1380 ) are given. Assuming the mixing angle between K 1 A and K 1 B to be θ K = 45 ° or −45°, we also give the detailed study for K 1 ( 1270 ) and K 1 ( 1400 ) . Using the conformal partial wave expansion, we obtain the models for light-cone distribution amplitudes, containing contributions up to conformal spin 9/2. It is interesting to note that some distribution amplitudes have significant asymmetric behaviors, which should be phenomenologically attractive.

Effect of Killer Impurities on Optical Properties of ZnO at Low Temperature

Optical characterizations for ZnO doped with killer impurities (Co or Fe or Ni) having doping concentrations 0.05–1.00% by weight have been carried out at 77 K. Optical properties such as excited state lifetime, trap-depth and decay constant values have been measured using the pulse excitation method. The effect of killer dopants, concentration of killer ions as well as the effect of temperature on various optical parameters values has been observed. Multi-exponential decay curves have been observed. Lifetime values are found to be in the micro- and nano-second time domain and a reverse trend is obtained with increase in concentration of killer impurities. With decreases in temperature from 300 to 77 K, lifetime shortening takes place. The effect of killer impurities is more prominent at higher concentrations. A mixed trend in decay constant values is observed with the increase proportional to the concentration of killer impurities. The values of the decay constant show a mixed effect with change in impurity concentrations. The value of the decay constant 0.76, corresponding to ZnO: Ni (0.7%) is the highest among all the doped ZnO phosphors.

A FINITE VOLUME MODEL FOR THE SOLUTION OF THE ADVECTION-DISPERSION EQUATION

ABSTRACT The present study is concerned with the modeling of conservative as well as non-conservative solute transport in ground water. The model is based on an operator split approach which uses an Eulerian frame work with finite volume method for the advective transport and fully implicit central difference method for the dispersive transport. This formulation helps in accurately simulating both highly advective and dispersive transport cases with less restriction on the grid size and time step. The numerical solution is compared with exact as well as the approximate analytical solution and the maximum error as percentage of peak concentration is presented for different values of decay constant at varying distances. It is found that finite volume method provides accurate solutions of both conservative and non-conservative solutes for both advection and dispersion dominated situations.

Fast photoluminescence decay processes of doped ZnS phosphors at low temperature

Singly and doubly doped ZnS phosphors have been synthesized in the laboratory. The crystal structure has been determined by X-ray diffraction (XRD) studies. Laser-induced photoluminescence has been observed in ZnS-doped phosphors when these were excited by the pulsed UV N 2 laser radiation at liquid nitrogen temperature (77 K). The temperature dependence of lifetimes, trap-depths and decay constant values were investigated for quencher impurities doped ZnS:Mn phosphors. The lifetimes of the orange emission from 4T 1– 6A 1 transition of Mn 2+ ions has been found to decrease at liquid nitrogen temperature. Due to downconversion phenomenon fast phosphorescence /fluorescence emission in the visible region is recorded in milliseconds time domain for ZnS:Mn while in case of ZnS:Mn, X (X=Fe, Co and Ni) phosphors lifetime reduces to nanoseconds time domain. A thermally activated carrier-transfer model has been proposed to explain the observed abnormal temperature behaviour of the lifetimes in ZnS:Mn, X (X=Fe, Co and Ni) phosphors. The high efficiency and fast recombination times observed in doped ZnS phosphors make these materials very attractive for optoelectronic applications.

Differential responses of litter decomposition to increased soil nutrients and water between two contrasting grassland plant species of Inner Mongolia, China

Soil chemistry and physical conditions are the key factors controlling litter decomposition. We studied the effects of increased soil nitrogen (N), phosphorus (P), and water on the decomposition rates and associated nutrient dynamics of two dominant grassland plant species (i.e. Allium bidentatum Fisch. ex Prokh. & Ikonn.-Gal. and Stipa krylovii Roshev.) with contrasting life forms and tissue chemistry in a typical steppe of Inner Mongolia, China. The treatments included addition of urea at the rates equivalent to 0, 8, 16, and 32 gN/m 2, and additions of mixed urea and triple superphosphate at the rates equivalent to 0, 8 gN/4 gP, 16 gN/8 gP, and 32 gN/16 gP/m 2, with and without water added. We found marked differences between the two species in the rates, as well as in the responses to water and addition rates of N and P, of litter decomposition. Additions of N alone or in mixture with P stimulated the rate of litter decomposition in both species. Adding water significantly increased the values of decay constant, k, in A. bidentatum, but not in S. krylovii. N and P concentrations in litters of A. bidentatum and S. krylovii all increased corresponding to increases in the rates of N or mixed N and P additions. Our results clearly indicate that the decomposition of high quality litter is more likely to be limited by soil moisture regimes, while that of low quality litter is more sensitive to nutrient availability. Our findings suggest that plant species with different litter qualities should be taken into consideration when we are to model the carbon cycle and nutrient dynamics in grassland ecosystems and that A. bidentatum is expected to contribute more than S. krylovii to the carbon cycle and nutrient dynamics of the semi-arid grasslands of Inner Mongolia.

Meteorite Phosphates Show Constant 176 Lu Decay Rate Since 4557 Million Years Ago

The use of radioactive decay of 176Lu to 176Hf to study the evolution of the Earth requires a precise and accurate value for the 176Lu decay constant. Recent determinations of this decay constant by age comparison to the more precisely calibrated U-Pb isotopic system produced internally consistent but discrepant values between terrestrial minerals and meteorites. New highly radiogenic Lu-Hf data for phosphate minerals from Richardton (ordinary chondrite) and Acapulco (primitive achondrite) yield decay constant values of 1.864 x 10(-11) +/- 0.016 x 10(-11) and 1.832 x 10(-11) +/- 0.029 x 10(-11) year(-1), respectively, identical to the value determined from terrestrial minerals.

Detection efficiency of fission tracks in apatite related to mica external detectors by the spike irradiation technique

Detection efficiency of fission tracks in non-annealed and annealed Durango apatite crystals related to mica external detectors for fission track dating was estimated experimentally using the spike irradiation technique [Suzuki, 2002a. Abstracts of 21st International Conference on Nuclear Tracks in Solids, p. 22]. The relation of the fission track density between apatite samples and mica external detectors is an important parameter for the determination of fission track ages using an absolute approach especially for crystalline minerals. Spike irradiation of uranium-235-induced fission fragments was carried out using a high uranium content glass, GE1497, fixed firmly on the sample surface. Experimental works were carried out for sections parallel and perpendicular to the crystallographic c -axis of apatite. The detection efficiency of fission tracks in non-annealed apatite related to the mica external detectors was estimated to be 0.90 for the prism face and 0.99 for the basal face. The fission track age of Durango apatite averaged for the prism and basal faces was estimated to be 30.6 ( ± 2.5 ) Ma, which is concordant with reference values reported previously, using the detection efficiency data with a B 0 value of the CN5 monitor glass and a U-238 spontaneous decay constant value of 8.46 × 10 - 17 a - 1 . The results also indicate that the B 0 age calibration method can be used effectively for the absolute evaluation of fission track ages of apatite.

Difference between the triton beta decay constants in atomic and molecular tritium measured by the helium isotope method

The results are given for an experiment on measuring the difference between the values of triton beta decay constant in atomic and molecular tritium, Δλam=λa−λm. In order to determine Δλam, the growth rates of the relative content of radiogenic helium-3 in samples with atomic and molecular tritium have been compared. The value of Δλam=(4.6±0.8)×10−12 s−1 has been obtained, which corresponds to a relative change of the decay constant by ∼0.26%. Using the value of Δλam measured, the following value of the half-life of atomic tritium has been derived: (T1/2)a=(12.264±0.018) years.

Couplings between pion and charmed mesons

We compute the couplings $DD^*\pi$,$D_1D^*\pi$,$D^*D^*\pi$, $D_1 D_1\pi$ using QCD sum rules. These couplings are important inputs in the meson exchange model calculations used to estimate the amount of $J/\psi$ absorption due to pions and rho mesons in heavy ion collisions. Our sum rules are constructed at the first order in the pion momentum $p_\mu$, which give the couplings that are not trivially related to the soft-pion theorem. Our calculated couplings, which somewhat depend upon the values of the heavy meson decay constants, are $g_{DD^*\pi}=8.2 \pm 0.1$, $g_{D_1 D^* \pi} = 15.8 \pm 2 {\rm GeV}$, $g_{D^* D^* \pi}= 0.3 \pm 0.03$ and $g_{D_1 D_1 \pi}= 0.17 \pm 0.04$.

A Selective Voltammetric Method to Follow the Hydrolytic Degradation of Nitrendipine and Nisoldipine

The development and application of a differential pulse voltammetric procedure for the hydrolytic degradation kinetic study of two well-known 1,4-dihydropyridine type drugs, nitrendipine and nisoldipine are presented. The DPV procedure exhibited an adequate selectivity, repeatability and reproducibility with CV lower than 2%. The recoveries were higher than 98% with CV of 1.63% and 1.87% for nitrendipine and nisoldipine, respectively. Hydrolysis of each drug was carried out in ethanol/Britton-Robinson buffer (30/70) at different pHs and at controlled temperature of 40, 60 and 80 °C. A significant degradation was observed at alkaline pH (>pH 8) following a first order kinetic for both drugs. At pH 12 the decay constant values of 4.85×10−2 h−1 for nitrendipine and 3.18×10−2 h−1 for nisoldipine were obtained. Also, activation energies of 18 kcal/mol and 16 kcal/mol for nitrendipine and nisoldipine, respectively, were calculated. Furthermore, for the nitrendipine hydrolytic, degradation test in different solutions for parenteral use were studied. All the tested vehicles significantly increased the degradation of the drug, with the composition of solutions being the most relevant factor rather than the pH.

Kinetic studies on veratryl alcohol transformation by horseradish peroxidase.

A number of peroxidases, such as lignin peroxidase and manganese peroxidase have proved to be useful for industrial applications. Some studies on the effects of temperature and pH stability have been carried out. It is known that veratryl alcohol increases their stability in the range 28-50 degrees C and is oxidized, leading to veratryl aldehyde formation. Similar results with horseradish peroxidase (HRP) in the presence of cofactors were found, but the oxidation of veratryl alcohol in the absence of cofactors was extremely labile at acid pH and inactivated in a few minutes. Considering the growing industrial application of HRP, knowledge of its stability and denaturation kinetics is required. In this study, horseradish peroxidase pool (HRP-VI) and its isoenzymes HRP-VIII (acid) and HRP-IX (basic) have been shown to catalyze the oxidation of veratryl alcohol to veratryl aldehyde in the presence of hydrogen peroxide at pH 5.8 in the 35-45 degrees C range and in the absence of any cofactors. Heat and pH denaturation experiments in the presence and absence of veratryl alcohol incubation were conducted with HRP-VI and HRP-IX isoenzymes. HRP-IX was the most active isoenzyme acting on veratryl alcohol but HRP-VI was the most stable for the temperature range tested. At 35 degrees C the HRP pool presented decay constant (Kd) values of 5.5 x 10(-2) h(-1) and 1.4 10(-2) h(-1) in the absence and presence of veratryl alcohol, respectively, with an effective ratio of 3.9. These results present a new feature of peroxidases that opens one more interesting application of HRP to industrial processes.

A method for intercalibration of U-Th-Pb and 40Ar- 39Ar ages in the Phanerozoic

The increasing analytical precision of 40Ar- 39Ar geochronological data and its use in studies that combine U-Pb and 40Ar- 39Ar data has necessitated derivation of a means to intercalibrate ages between the two isotopic systems. The primary determinants inhibiting accurate cross calibration are uncertainty in decay constant values and uncertainty in 40Ar∗/ 40K (usually presented as apparent age) for 40Ar- 39Ar standards, notably those derived from the Fish Canyon Tuff. By utilizing a monazite- and biotite bearing Oligocene ash flow tuff (MAC-83) as the primary standard material, precise U-Th-Pb and 40Ar- 39Ar ages can be derived. Because both isotopic systems should reflect closure during the instantaneous eruption event, the 24.21 ± 0.10 Ma 207Pb/ 235U age should match the age resulting from 40Ar- 39Ar biotite analysis. This forced equivalence will partly offset the effects of decay constant uncertainty. Furthermore, by co-irradiating Fish Canyon Tuff sanidine with MAC-83 biotite, the apparent age for Fish Canyon Tuff sanidine is back-calculated to 27.98 ± 0.15 Ma, relative to the MAC-83 207Pb/ 235U age. Hence, intercalibration between the two isotopic systems in a relative sense can be accomplished, allowing for a direct and valid comparison of ages. It is also shown that forcing equivalence of the two isotopic systems minimizes the effect of decay constant uncertainty for samples of Phanerozoic age.

Transient and steady‐state conduction in ethyl cellulose (EC)–poly(methyl methacrylate) (PMMA) blends

Transient discharging currents and steady-state conduction in solution-grown ethyl cellulose (EC)–poly(methyl methacrylate) (PMMA) blends measured as a function of temperature (30–80 °C) and field strength (10–100 kV cm−1) are reported. Transient currents are found to follow the Curie–VonSchweidler law, characterized by different slopes in short- and long-time regions, having different decay constant values lying between 0.75–0.99, and 1.68–1.95. The corresponding activation energies are found to increase with time of measurement of discharge current. Isochronal characteristics (ie current versus temperature plots at constant times) constructed from the data seem to reveal a broad peak observed at 60 °C. The dependence of dark current at different temperatures (30–80 °C) in a metal (1)–EC–PMMA blend–metal (1)/(2) system on the applied voltage in the range 10–100 kV cm−1 has also been studied; the current is found to be strongly temperature dependent. Dipole polarization and space charge resulting from trapping of injected charge carriers in energetically distributed traps and induced dipoles created because of the piling up of charge carriers at the phase boundary of the heterogeneous components of the blend are considered to account for the observed transient currents. The results of current–voltage measurement on blends are interpreted to show that the low-field steady-state conduction is ohmic in nature, and in high fields the charge carriers are generated by field-assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material by a hopping process between the localized states by a Jonscher–Ansari Poole–Frenkel mechanism. The modified P–F barrier is calculated to be 1.89 × 10−19 J (1.18 eV), 1.92 × 10−19 J (1.20 eV) and 1.95 × 10−19 J (1.22 eV) for P1, P2 and P3 blends, respectively. © 2000 Society of Chemical Industry

Spectral Hardness Decay with Respect to Fluence in BATSE Gamma‐Ray Bursts

We have analyzed the evolution of the spectral hardness parameter Epk as a function of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts with the trend reported by Liang & Kargatis (1996) which found that Epk decays exponentially with respect to photon fluence. We also fit these pulses with a slight modification of this trend, where Epk decays linearly with energy fluence. In both cases, we found the set of 41 pulses to be consistent with the trend. For the latter trend, which we believe to be more physical, the distribution of the decay constant is roughly log-normal, with a mean of 1.75 +/- 0.07 and a FWHM of 1.0 +/- 0.1. Regarding an earlier reported invariance in the decay constant among different pulses in a single burst, we found probabilities of 0.49 to 0.84 (depending on the test used) that such invariance would occur by coincidence, most likely due to the narrow distribution of decay constant values among pulses.

Primary photophysical properties of 4H-1-benzopyran-4-thione in cyclodextrin complexes

The influence of cyclodextrins (CDs) on the photophysics of 4H-1-benzopyran-4-thione (BPT) has been studied in solution and in the solid state by steady-state absorption, emission and circular dichroism as well as by time-resolved diffuse reflectance laser flash photolysis. The spectral changes and induced circular dichroism indicate the formation of the cyclodextrin complexes of BPT. The very low fluorescence quantum yield from the S 2 state for this complex, similar to that measured for BPT alone in water, suggests that there is an interaction between water and guest molecules in the CD complexes leading to shortening of the S 2 state lifetime. The Albery model was used to analyse the phosphorescence of the BPT·β-CD solid complex. The values obtained for the average rate constants, , are similar to values of the triplet state decay constant of the thioketone in inert solvents at infinite dilution, k 0 . Quenching by oxygen does not play an important role when thioketones are included within cyclodextrins in the solid state.

Analog simulations of Josephson junction in a microwave field. Devil's staircase, fractal dimension, and decay constants

The RSJ model of the Josephson junction in the presence of a microwave field is studied using an analog computer, with special attention to the behavior of this system near or at the critical line, where the set of substeps forms a complete devil's staircase on theI-V characteristic. A value of fractal dimensionD=0.868±0.002 is determined from 240 substeps between the winding numbersW=0 andW=1. Four values of decay constants are determined. The results agree very well with the prediction obtained from the one-dimensional circle map. A self-similarity graph is shown confirming that the staircase is very near the critical line. Results confirm the universal and global character ofD and decay constants on the critical line, as was suggested by Jensen et al.

Formula omitted] and K/Ar dating of the bishop and fish canyon tuffs: Calibration ages for fission-track dating standards

Ambiguous values of the 238U spontaneous fission decay constant and complexities of absolute neutron dosimetry underline the dependency of fission-track dating upon age standards. New K/Ar and 40 Ar 39 Ar step-heating data are presented for two putative standards: the Bishop Tuff, California and the Fish Canyon Tuff, Colorado. Measured K/Ar ages of 0.741 ± 0.014 Ma for Bishop Tuff sanidine and 27.4 ± 0.4 Ma for the Fish Canyon Tuff (mean of concordant results on biotite, sanidine, hornblende and plagioclase) show good agreement with previous results. 40 Ar 39 Ar plateaus for Bishop Tuff sanidine (plateau age 0.734 ±0.024 Ma) and Fish Canyon Tuff biotite (plateau age 27.8 ± 0.2 Ma) suggest minimal thermal disturbance since deposition of the tuffs, supporting the underlying assumption of equality of their fission-track and argon ages.

A model for augmentation of hepatocyte response to pulsatile glucagon stimuli.

We have reported that in the physiological concentration range pulsatile glucagon delivery (6 pulses in 90 min) is a more effective stimulus of rat hepatocyte glucose production than is continuous infusion of the same amount of hormone (pulsatile EC50 = 186 +/- 41 pg/ml, continuous EC50 = 884 +/- 190 pg/ml). At supraphysiological glucagon concentrations, however, the maximal response to continuous glucagon infusion exceeds the response to pulses (241 +/- 14 vs. 140 +/- 11 mumol X G-1 X 90 min-1). In an effort to explain these observations we derived a model for the 90-min hepatocyte responses to pulsatile and continuous glucagon delivery based on the waveform of the hepatocyte response to a transient glucagon stimulus. The model demonstrated that the time constant for response decay was an important determinant of the relative efficacy of the two patterns of hormone delivery. For the observed decay constant value of 0.132 +/- 0.02 min-1 the model predicted the following dose-response parameters: pulsatile EC50 = 131 pg/ml, Rmax = 119 mumol X G-1 X 90 min-1, continuous EC50 = 656 pg/ml, Rmax = 272 mumol X G-1 X 90 min-1. The ability of a model based only on the kinetics of a single pulse to simulate the observed dose-response relationship suggests that pulsatile stimulation is intrinsically more effective than continuous hormonal stimulation.