<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20001102//EN" "svg-20001102.dtd">
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 800 400"
 xmlns:xlink="http://www.w3.org/1999/xlink">
<desc>Produced by GNUPLOT 4.0 patchlevel 0 </desc>

<defs>


	<circle id='gpDot' r='1'/>
	<path id='gpPt0' style='stroke-width:0.222' d='M-1,0 h2 M0,-1 v2'/>
	<path id='gpPt1' style='stroke-width:0.222' d='M-1,-1 L1,1 M1,-1 L-1,1'/>
	<path id='gpPt2' style='stroke-width:0.222' d='M-1,0 L1,0 M0,-1 L0,1 M-1,-1 L1,1 M-1,1 L1,-1'/>
	<rect id='gpPt3' style='stroke-width:0.222' x='-1' y='-1' width='2' height='2'/>
	<use xlink:href='#gpPt3' id='gpPt4' style='fill:currentColor; stroke:none'/>
	<circle id='gpPt5' style='stroke-width:0.222' cx='0' cy='0' r='1'/>
	<use xlink:href='#gpPt5' id='gpPt6' style='fill:currentColor; stroke:none'/>
	<path id='gpPt7' style='stroke-width:0.222' d='M0,-1.33 L-1.33,0.67 L1.33,0.67 z'/>
	<use xlink:href='#gpPt7' id='gpPt8' style='fill:currentColor; stroke:none'/>
	<use xlink:href='#gpPt7' id='gpPt9' transform='rotate(180)'/>
	<use xlink:href='#gpPt9' id='gpPt10' style='fill:currentColor; stroke:none'/>
	<use xlink:href='#gpPt3' id='gpPt11' transform='rotate(45)'/>
	<use xlink:href='#gpPt11' id='gpPt12' style='fill:currentColor; stroke:none'/>
</defs>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,337 L782,337 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,337 L75,337 M782,337 L791,337 '></path>
	<g transform="translate(67,341)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:end">
		<text> 0</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,255 L782,255 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,255 L75,255 M782,255 L791,255 '></path>
	<g transform="translate(67,259)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:end">
		<text> 0.5</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,173 L782,173 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,173 L75,173 M782,173 L791,173 '></path>
	<g transform="translate(67,177)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:end">
		<text> 1</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,91 L782,91 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,91 L75,91 M782,91 L791,91 '></path>
	<g transform="translate(67,95)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:end">
		<text> 1.5</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,9 L782,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,9 L75,9 M782,9 L791,9 '></path>
	<g transform="translate(67,13)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:end">
		<text> 2</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M84,337 L84,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,337 L84,346 M84,9 L84,0 '></path>
	<g transform="translate(84,368)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text> 2000</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M259,337 L259,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M259,337 L259,346 M259,9 L259,0 '></path>
	<g transform="translate(259,368)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text> 2002</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M433,337 L433,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M433,337 L433,346 M433,9 L433,0 '></path>
	<g transform="translate(433,368)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text> 2004</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M608,337 L608,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M608,337 L608,346 M608,9 L608,0 '></path>
	<g transform="translate(608,368)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text> 2006</text>
	</g>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:0.20">
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:0.20">
	<path d='M782,337 L782,9 '></path>
</g>
<g style="fill:none; color:gray; stroke:currentColor; stroke-width:1.00">
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M782,337 L782,346 M782,9 L782,0 '></path>
	<g transform="translate(782,368)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text> 2008</text>
	</g>
	<path d='M84,337 L782,337 L782,9 L84,9 L84,337 '></path>
	<g transform="translate(22,173) rotate(-90)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text>Number of references</text>
	</g>
	<g transform="translate(433,395)" style="stroke:none; fill:black; font-family:sans-serif; font-size:12.00; text-anchor:middle">
		<text>Year of publication</text>
	</g>
</g>
<g style="fill:none; color:red; stroke:currentColor; stroke-width:1.00">
	<path d='M302,337 L389,337 L302,337 M389,337 L389,9 L477,9 L477,337 L389,337 M477,337 L564,337 
		L477,337 '></path>
</g>
<g style="fill:none; color:black; stroke:currentColor; stroke-width:1.00">
	<path d='M84,337 L782,337 L782,9 L84,9 L84,337 '></path>
</g>
</svg>

