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        <span style="font-family:SimSun;">Hi all！</span> 
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        <span style="font-family:SimSun;"> </span> 
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        <span style="font-family:SimSun;">I met some problems when trying to add the resistivity η to the simulation
of <strong>magnetoHD/NohCylindrical(user manual 32.2.4)</strong>,</span> 
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        <span style="font-family:SimSun;"> </span> 
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        <span style="font-family:SimSun;">First, the units of resistivity troubles me. In the CGS UnitSystem,
whether setting </span><i><span style="font-family:SimSun;"> <strong>resistivity = 1 </strong></span></i><span style="font-family:SimSun;">in </span><i><span style="font-family:SimSun;">“flash.par” </span></i><span style="font-family:SimSun;">means set magnetic resistivity η=1
cm</span>^{<span style="font-family:SimSun;">2</span>}<span style="font-family:SimSun;">/s=10</span>^{<span style="font-family:SimSun;">-11 </span>}<span style="font-family:SimSun;">Ω·m and magnetic viscosity
υ</span>_{<span style="font-family:SimSun;">m</span>}<span style="font-family:SimSun;">=η·c·c/(4·pi), where c=3·10</span>^{<span style="font-family:SimSun;">10 </span>}<span style="font-family:SimSun;">cm/s?</span> 
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        <span style="font-family:SimSun;"> </span> 
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        <span style="font-family:SimSun;">Second, the calculation about resistivity troubles me. Looking through
the kernels and helpers of Diffuse Unit, I can’t find any calculation about resistivity.
Is it in the kernels and helpers of <strong>Hydro Unit</strong>? I can’t find the calculation about <strong>magnetic diffusion</strong> in the Hydro Unit. Is it needed to </span><em><span style="font-family:Times New Roman;"><strong>REQUIRE Diffuse</strong></span></em><span style="font-family:SimSun;">?</span> 
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        <span style="font-family:SimSun;"> </span> 
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        <span style="font-family:SimSun;">Finally, When I set these parameter in </span><i><span style="font-family:SimSun;">“flash.par”</span></i><span style="font-family:SimSun;"> as below and setup with </span><i><span style="font-family:Times New Roman;"><strong>+usm</strong></span></i> 
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                <i><span style="font-family:Times New Roman;"><strong>#     Units
(none, SI or CGS)</strong></span></i> 
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                <i><span style="font-family:Times New Roman;"><strong>UnitSystem        = "CGS"</strong></span></i> 
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                <i><span style="font-family:Times New Roman;"><strong>##   
Resistive MHD parameters     ##</strong></span></i> 
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                <i><span style="font-family:Times New Roman;"><strong>useDiffuse    =
.true.</strong></span></i> 
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                <i><span style="font-family:Times New Roman;"><strong> dt_diff_factor 
= 0.8</strong></span></i> 
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                <i><strong><span style="font-family:Times New Roman;">useMagneticResistivity     = .true.</span></strong></i> 
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                <i><strong><span style="font-family:Times New Roman;"><span class="ke-content-forecolor" style="color:#E53333;"> resistivity          = 0.0</span> # magnetic Resistivity</span></strong></i> 
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<p>
        mpirun stopped with the same message, even if setting a large range of <i>resistivity</i>, from 10²⁰ to 10^-40
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        <b><i>      DRIVER_ABORT:
[Hydro]: Computed dt is not positive! Aborting!</i></b> 
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        <b><i>      dtCheck=   0.0000000000000000</i></b><b></b> 
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        <br>
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        How to solve these problem? Really need someone to help!
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<p>
        Zhang
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