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$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90]{8607fig1.ps} \end{figure}$ Figure 1: [O/Fe] abundance ratio versus oxygen abundance [O/H]. The dashed and dotted lines are drawn for convenience.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig2.ps} \end{figure}$ Figure 2: Sulfur to iron abundance ratio, [S/Fe], versus sulfur abundance relative to solar, [S/H]. The lines are drawn for convenience.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig3.ps} \end{figure}$ Figure 3: Oxygen abundance relative to solar, [O/H], versus silicon abundance [Si/H]. Dotted line is for [O/H] = [Si/H].
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig4.ps} \end{figure}$ Figure 4: [N/O] abundance ratio versus neutral hydrogen column density log N(H I). The vertical dotted line indicates the standard definition of DLA systems (log N(H I) > 20.3).
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In the text

$\begin{figure} \par\includegraphics[width=6.5cm,angle=-90,clip]{8607fig5.ps} \end{figure}$ Figure 5: Histogram of [N/O] abundance ratios for the 13 systems with definite measurements in our sample.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig6.ps} \end{figure}$ Figure 6: Nitrogen to oxygen abundance ratio, [N/O], versus nitrogen abundance [N/H]. [X/H] = (X/H) - (X/H) $_{\odot }$ .
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In the text

$\begin{figure} \par\includegraphics[width=7cm,angle=-90,clip]{8607fig7a.ps} \includegraphics[width=7cm,angle=-90,clip]{8607fig7b.ps} \end{figure}$ Figure 7: Upper panel: nitrogen to oxygen abundance ratio, [N/O], versus oxygen abundance [O/H]. [X/H] = (X/H)-(X/H) $_{\odot }$ . The range for the local primary plateau is indicated as two horizontal dashed lines at [N/O] = -0.57 and -0.74. The other dashed line indicates the expected position in case of secondary production: the line is the extrapolation at low [N/O] values of local measurements. Lower panel: same as above using the absolute abundances (X/H) = log N(X) - log N(H) with X = O or N. The dots and crosses indicate local measurements from dwarf-irregular galaxy HII regions (crosses; van Zee & Haynes 2006), HII regions in spiral galaxies (crosses; van Zee et al. 1998), metal-poor emission line galaxies (dots; Nava et al. 2006), HII regions in BCD galaxies (dots; Izotov & Thuan 2004) and emission-line galaxies from SDSS (dots; Izotov et al. 2006).
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=0,clip]{8607fig8a.ps} \inc... ....ps} \includegraphics[width=7.5cm,angle=0,clip]{8607fig8d.ps}\par \end{figure}$ Figure 8: N I and O I absorption lines in the DLA systems: Q 0102-190, z = 2.926; Q 0112-306, z = 2.418; Q 0841+129, z = 2.476 and Q 0913+072, z = 2.618 from top to bottom, respectively. Model fits are overplotted.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=0,clip]{8607fig9a.ps} \inc... ....ps} \includegraphics[width=7.5cm,angle=0,clip]{8607fig9d.ps}\par \end{figure}$ Figure 9: N I and O I absorption lines in the DLA systems: Q 1108-077, z = 3.608; Q 1337+113, z = 2.508; Q 1337+113, z = 2.796 and Q 1340-136, z = 3.118 from top to bottom, respectively. Model fits are overplotted.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,angle=0,clip]{8607fig10a.ps}\vsp... ...m} \includegraphics[width=7.6cm,angle=0,clip]{8607fig10d.ps}\par \end{figure}$ Figure 10: N I and O I absorption lines in the DLA systems: Q 1409+095, z = 2.456; Q 1409+095, z = 2.668; Q 2059-360, z = 3.083 and Q 2332-094, z = 3.057 from top to bottom, respectively. Model fits are overplotted.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90]{8607fig1.ps} \end{figure}$	Figure 1: [O/Fe] abundance ratio versus oxygen abundance [O/H]. The dashed and dotted lines are drawn for convenience.
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig2.ps} \end{figure}$	Figure 2: Sulfur to iron abundance ratio, [S/Fe], versus sulfur abundance relative to solar, [S/H]. The lines are drawn for convenience.
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig3.ps} \end{figure}$	Figure 3: Oxygen abundance relative to solar, [O/H], versus silicon abundance [Si/H]. Dotted line is for [O/H] = [Si/H].
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig4.ps} \end{figure}$	Figure 4: [N/O] abundance ratio versus neutral hydrogen column density log N(H I). The vertical dotted line indicates the standard definition of DLA systems (log N(H I) > 20.3).
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$\begin{figure} \par\includegraphics[width=6.5cm,angle=-90,clip]{8607fig5.ps} \end{figure}$	Figure 5: Histogram of [N/O] abundance ratios for the 13 systems with definite measurements in our sample.
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=-90,clip]{8607fig6.ps} \end{figure}$	Figure 6: Nitrogen to oxygen abundance ratio, [N/O], versus nitrogen abundance [N/H]. [X/H] = (X/H) - (X/H) $_{\odot }$ .
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=0,clip]{8607fig8a.ps} \inc... ....ps} \includegraphics[width=7.5cm,angle=0,clip]{8607fig8d.ps}\par \end{figure}$	Figure 8: N I and O I absorption lines in the DLA systems: Q 0102-190, z = 2.926; Q 0112-306, z = 2.418; Q 0841+129, z = 2.476 and Q 0913+072, z = 2.618 from top to bottom, respectively. Model fits are overplotted.
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$\begin{figure} \par\includegraphics[width=7.5cm,angle=0,clip]{8607fig9a.ps} \inc... ....ps} \includegraphics[width=7.5cm,angle=0,clip]{8607fig9d.ps}\par \end{figure}$	Figure 9: N I and O I absorption lines in the DLA systems: Q 1108-077, z = 3.608; Q 1337+113, z = 2.508; Q 1337+113, z = 2.796 and Q 1340-136, z = 3.118 from top to bottom, respectively. Model fits are overplotted.
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$\begin{figure} \par\includegraphics[width=7.6cm,angle=0,clip]{8607fig10a.ps}\vsp... ...m} \includegraphics[width=7.6cm,angle=0,clip]{8607fig10d.ps}\par \end{figure}$	Figure 10: N I and O I absorption lines in the DLA systems: Q 1409+095, z = 2.456; Q 1409+095, z = 2.668; Q 2059-360, z = 3.083 and Q 2332-094, z = 3.057 from top to bottom, respectively. Model fits are overplotted.
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