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We examined the effects of biochar and urease inhibitors/nitrification inhibitors on nitrification process, ammonia and N2O emission in subtropical soil, and determined the best combination of biochar with nitrification and urease inhibitors. This work could provide a theoretical basis for the mitigation of the negative environmental risk caused by reactive nitrogen gas in the application of nitrogen fertilizer. A indoor aerobic culture test was conducted with seven treatments [ urea+biochar (NB ), urea+nitrification inhibitor (N + NI), urea+urease inhibitor (N+UI), urea+nitrification inhibitor+urease inhibitor (N+NIUI), urea+nitrification inhibitor+biochar (NB+NI), urea+urease inhibitor+biochar (NB+UI), urea+nitrification inhibitor+urease inhibitor+biochar (NB+NIUI) ] and urea (N) as the control. The dynamics of soil inorganic nitrogen content, N2O emission and the volatility of ammonia volatilization were observed under combined application of biochar with urease inhibitor (NBPT) /nitrification inhibitor (DMPP). The results showed that: 1) Compared to the control (5.11 mg N · kg-1 · d-1) during the incubation period, NB treatment significantly increased the rate constant of nitrification by 33.9%, and N+NI treatment significantly reduced the nitrification rate constant by 22.9%. NB treatment significantly increased the abundance of ammonia oxidizing bacteria (AOB) by 56.0%. 2) Compared with N treatment, N+NI and NB+NI treatments significantly enhanced the cumulative emission of NH3 by 49%. The N + UI treatment reduced the cumulative loss of NH3. The inhibition effect of NB+UI treatment was more significant. 3) The emission rate of N2O was highest in the first 10 days after fertilization. The N2O emission under NB treatment was the earliest, and that of N treatment was the highest (5.87 µg · kg-1 · h-1). The combined application of DMPP and NBPT performed the best in reducing soil N2O emission. We estimated global warming potential (GWP) of the direct N2O and indirect N2O (NH3) emissions. Compared with N treatments, N+NI and NB+NI treatments increased the GWP by 34.8% and 40.9%, respectively. While the NB and NB+UI treatments significantly reduced the GWP by 45.9% and 60.5%, the combination of biochar and urease inhibitor had the best effect on reduction of GWP of soil active nitrogen emissions. [ABSTRACT FROM AUTHOR]

We have used a new millimeter-resolution MRI-based model of the human body to calculate the electromagnetic absorption in the head and neck for three experimental Yagi antennas suggested for the handheld transceivers of a proposed 6-GHz personal communication network (PCN) system. The SAR distributions are obtained with a resolution of 1.974 x 1.974 x 1.5 mm for the transceivers that are held against the ears and tilted forward by 33 [degrees]. The finite-difference time-domain technique is used to calculate the EM fields and SAR's for the transceiver, antenna, and head and neck coupled region that is divided into 158 x 84 x 188 or nearly 2.5 million cells. The highlights of the numerical calculations are verified by means of a head-shaped experimental model made of tissue-equivalent materials simulating the electrical properties ([[Epsilon].sub.r], [Sigma]) of skull, brain, muscle, eyes, and ears developed for use at 6 GHz. Because of the proximity to the antenna, the highest SAR's are obtained for the upper part of the ear. For a planned radiated power of 0.6 W, the peak SAR's averaged over any 1 g of tissue defined as a tissue volume in the shape of a cube are on the order of 0.5-1.0 W/kg for two of the proposed antennas and considerably higher (2.06 W/kg) for the third antenna using a narrower off-axis reflector. Low SAR's for the first two antennas are likely due to the shielding provided by the relatively wider strip reflector plates used for these antennas.

The finite-difference time-domain (FDTD) and frequency dependent finite difference time-domain [(FD).sup.2]TD methods have been previously used to calculate internal electric (E) fields and induced currents for exposure of the anatomically based model of the human body to electromagnetic pulses (EMPs) and continuous wave (CW) sinusoids. The limitation of these methods is that a complete, computer resource intensive, simulation must be done for each different waveform of interest. This paper describes a simple and efficient technique based on convolution theory which provides the response of the body to any incident waveform (EMP or CW) from a single simulation with an incident impulse waveform. This allows the impulse response to be stored, and the response of the body to any desired waveform to be efficiently computed on a small computer or PC.

This paper describes the use of the previously formulated Frequency-Dependent Finite-Difference Time-Domain ((FD) squared TD) method for analysis of an anatomically based heterogeneous man model exposed to ultra-wide-band electromagnetic pulse sources. The human tissues' electrical permittivities, Epsilon(super *)(sub i) (Omega), are described by Debye equations with two relaxation constants, and the equation D(t) = Epsilon(super *) (Omega)E(t) is converted to a finite-difference equation along with the Maxwell's equations used by the standard FDTD method. Using a single run with a broad-band pulse excitation, the (FD) squared TD method is used to calculate mass normalized rates of energy deposition (specific absorption rates or SAR's) and induced currents in the man model over a broad band of frequencies. Time-domain coupling of a representative ultrashort pulse of subnanosecond rise time and nanosecond pulse duration to the human body is also examined.

A weakness of the finite-difference time-domain (FDTD) method is that dispersion of the dielectric properties of the scattering/absorbing body is often ignored and frequency-independent properties are generally taken. While this is not a disadvantage for CW or narrow-band irradiation, the results thus obtained may be highly erroneous for short pulses where ultrawide bandwidths are involved. In some recent publications, procedures based on a convolution integral describing D(t) in terms of E(t) are given for media for which the complex permittivity Epsilon(super *)(Omega) may be described by a single-order Debye relaxation equation or a modified version thereof. Procedures are, however, needed for general dispersive media for which Epsilon(super *)(Omega) and mu(super *)(Omega) may be expressible in terms of rational functions, or for human tissues where multiterm Debye relaxation equations must generally be used. We describe a new differential equation approach, which can be used for general dispersive media. In this method D(t) is expressed in terms of E(t) by means of a differential equation involving D, E, and their time derivatives. The method is illustrated by means of one- and three-dimensional examples of media for which Epsilon(super *)(Omega) is given by a multiterm Debye equation, and for an approximate two-thirds muscle-equivalent model of the human body.