Effects of ammonium sulphate application on the rhizosphere,fine-root and needle chemistry in aPicea abies (L.) Karst. stand

Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation pattern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatments started in 1988. Current year needles, one-year-old needles and cylindrical core samples of the LFH-layer and the mineral soil layers were sampled in 1988, 1989 and 1990. Compared to the control plots, pH decreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO₄-S concentration increased significantly. Aluminium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0–10 cm depths, both in 1989 and 1990. Calcium, Mg and K concentrations also increased after treatment with ammonium sulphate. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar trend was found in the needles. Ca concentrations in fine roots were significantly lower in the NS plots in the LFH layer in 1990 and the same pattern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots. It was suggested that NS treatment resulted in displacement of Mg, Ca and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

Effects of ammonium sulphate application on the chemistry of bulk soil,rhizosphere, fine roots and fine-root distribution in a Picea abies (L.) karst. stand

The effect of ammonium sulphate application on the bulk and rhizosphere soil chemistry, elemental concentration of living fine roots (<2 mm in diameter), amounts of living and dead fine roots, root length density and specific root length density were investigated in a 28 year old Norway spruce stand in SW Sweden. The treatments started in 1988. Core samples of the LFH layer and mineral soil layers were sampled in control (C) and ammonium sulphate (NS) treatment plots in 1988, 1989 and 1990. Soil pH and NO₃-S and SO₄-S, Al, Ca, Mg, Mn and K concentrations were measured for both the bulk soil and rhizosphere soil.The pH-values of the bulk and rhizosphere soil decreased in 1989 and 1990 in NS plots compared to control plots, while the SO₄-S concentration increased. The Ca, Mg and K concentration increased in the NS treatment in almost all layers in the bulk and the rhizosphere soil. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment reduced Mg concentration in fine roots in all layers in 1990. The Al concentrations in the rhizosphere and bulk soil were higher in NS plots in all layers, except at 0–10 cm depth, both in 1989 and 1990. The Al content of living fine roots was higher in NS plots than C plots but the differences were not significant. The NS addition did not affect the P and K contents of fine roots in any soil layer, but the S concentrations of fine roots were significantly higher in NS plots in 1989 and 1990. The fine root necromass was higher in NS than in C in 1990, in the LFH layer, indicating a gradual decrease in the vitality of the fine roots. It was suggested that the NS treatment resulted in displacement of Mg and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

Control of a one-link arm by burst signal generators

 The focus of this paper is the study of stability and point-to-point movement of a one-link arm. The sagittal arm has two musculotendon actuators, two neural oscillators that generate burst signals as motoneuron inputs, and spindles and Golgi tendon organs for extrinsic reflex feedbacks. It is shown that coactivation leads to intrinsic position and velocity feedback, and that the tendons introduce intrinsic force and rate of force feedback. In addition, the integrating effects of the tendons are studied when the actuator is constructed from a large number of identical fibers that are excited by alpha signals whose arrival times at the fiber are randomly distributed. Each of the musculotendon actuators receives two input signals – a burst signal analogous to alpha inputs and a conventional analogue signal that represents fusimotor input to the spindles. The process of combining burst signals and conventional analogue signals is studied. Simulation results show that the movement of the system with burst signals as inputs has overshoot and speed similar to the system with analogue signals. Received: 30 May 1994/Accepted in revised form: 13 January 1995     

Efficacy of pesticides on the functional response on larval ectoparasitoid,Habrobracon hebetor Say (Hymenoptera: Braconidae)

Exposing to sub-lethal and low lethal doses of pesticides may cause changes in natural enemy behavioural, such as functional, response. In this study, the effects of chlorpyrifos, carbaryl, abamectin and spinosad were evaluated on the functional response of the Habrobracon hebetor to different densities of last instar larvae of Anagasta kuehniella Zeller. Young adult females of the parasitoid were exposed to LC₃₀ of chlorpyrifos, carbaryl, abamectin and spinosad that were 0.32, 4.03, 3.05 and 17.51?mg a.i./l for 24?h, respectively. Host densities of 2, 4, 8, 16, 32 and 64 were offered to treated young females for 2?h in 10-cm Petri dishes and then the parasitism data were recorded. Experiments were conducted in eight replications. Functional response type was determined using logistic regression and the parameters were appraised by non-linear regression using statistical analysis software. Functional response was type Ш in control and insecticide treatments. Searching efficiency in control, chlorpyrifos-, carbaryl-, abamectin- and spinosad-treated wasps were 0.008?±?0.002, 0.002?±?0.0009, 0.0034?±?0.0013, 0.0076?±?0.002 and 0.0073?±?0.002?h^?1and handling times were 1.38?±?0.1, 7.64?±?1.01, 3.3?±?0.315, 1.55?±?0.1 and 1.46?±?0.11?h, respectively. Chlorpyrifos and carbaryl had the highest effect on searching efficiency of H. hebetor. Spinosad and abamectin showed less adverse effect on the functional response parameters. Finally, after conducting the advanced field studies, spinosad and abamectin may be used as a compatible chemical material with biological control agent in integrated pest management programmes.     

Synthesis of novel azo compounds containing 5(4H)-oxazolone ring as potent tyrosinase inhibitors

Six new azo dyes containing of 5(4H)-oxazolone ring were prepared by diazotization of 4-aminohippuric acid and coupling with N,N-dimethylaniline, 1-naphthol and 2-naphthol and condensation with 4-fluoro benzaldehyde or 4-trifluoromethoxy benzaldehyde. The new compounds were fully characterized by spectroscopic techniques. All synthesized compounds exhibited high tyrosinase inhibitory behavior. The results of mushroom tyrosinase inhibition assays indicate that the 4-trifluoromethoxy derivatives have high degrees of inhibition and N,N-dimethylaniline derivatives are better for tyrosinase inhibition than 1-naphthol and 2-naphthol derivatives. All synthesized azo compounds (4a–4f) showed the most potent mushroom tyrosinase inhibition, comparable to that of Kojic acid and l-mimosine, as reference standard inhibitors.     

Association Between Hypertension in Healthy Participants and Zinc and Copper Status: a Population-Based Study

Biological Trace Element Research - The prevalence of hypertension (HTN) is increasing globally. It has been shown that there is an association between micronutrient deficiency and HTN. In the...     

The response of tissue-equivalent proportional counters to heavy ions

The paper presents a theoretical model for the response of a tissue-equivalent proportional counter (TEPC) irradiated with charged particles. Heavy ions and iron ions in particular constitute a significant part of radiation in space. TEPCs are used for all space shuttle and International Space Station (ISS) missions to estimate the dose and radiation quality (in terms of lineal energy) inside spacecraft. The response of the tissue-equivalent proportional counters shows distortions at the wall/cavity interface. In this paper, we present microdosimetric investigation using Monte Carlo track structure calculations to simulate the response of a TEPC to charged particles of various LET (1 MeV protons, 2.4 MeV alpha particles, 46 MeV/nucleon 20Ne, 55 MeV/nucleon 20Ne, 45 MeV/nucleon 40Ar, and 1.05 GeV/nucleon 56Fe). Data are presented for energy lost and energy absorbed in the counter cavity and wall. The model calculations are in good agreement with the results of Rademacher et al. (Radiat. Res. 149, 387-389, 1998), including the study of the interface between the wall and the sensitive region of the counter. It is shown that the anomalous response observed at large event sizes in the experiment is due to an enhanced entry of secondary electrons from the wall into the gas cavity.     

The effect of model approximations on single-collision distributions of low-energy electrons in liquid water

The development of cross sections for the inelastic interaction of low-energy electrons with condensed tissue-like media is best accomplished within the framework of the dielectric theory. In this work we investigate the degree to which various model approximations, used in the above methodology, influence electron single-collision distributions. These distributions are of major importance to Monte Carlo track structure codes, namely, the energy-loss spectrum, the inelastic inverse mean free path, and the ionization efficiency. In particular, we make quantitative assessment of the influence of (1) the optical data set, (2) the dispersion algorithm, and (3) the perturbation and exchange Born corrections. It is shown that, although the shape and position of the energy-loss spectrum remains almost fixed, its peak height may vary by up to a factor of 1.5. Discrepancies in the calculated inelastic inverse mean free path are largely within 20-30% above 100 eV; they increase drastically, though, at lower energies. Exchange and perturbation Born corrections increase gradually below 1 keV leading to a approximately 30 to 40% reduction of the inverse mean free path at 100 eV. The perturbation effect contributes more than the exchange effect to this reduction. Similar to the dispersion situation, the effect of Born corrections at lower energies is also unclear since the models examined disagree strongly below 100 eV. In comparison, the vapor data are higher than the liquid calculations by 20 to 50% as the energy decreases from 1 to 0.1 keV, respectively. The excitation contribution is the main cause of this difference, since the ionization efficiency in the liquid levels off at approximately 90%, whereas the plateau value for the vapor is approximately 70%. It is concluded that electron inelastic distributions for liquid water, although in some respects distinctively different from the vapor phase, have associated uncertainties that are comparable in magnitude to the phase differences. The situation below 100 eV is uncertain.