diff --git a/R/utils.R b/R/utils.R
index 30df041..2d4b6db 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -177,8 +177,9 @@ ipdf <- function(file, ...) {
 #'   plot(1:5)
 #'   dev.off()
 #' 
+#'   pngfile <- file.path(tmpdir, "test.png")
 #'   pdf2png(pdffile)
-#'   pdf2png(pdffile, outfile="test.png")
+#'   pdf2png(pdffile, outfile=pngfile)
 #' 
 #'   testfile <- system.file("/doc/intro.pdf", package="limma")
 #'   if(file.exists(testfile)) {
diff --git a/man/pdf2png.Rd b/man/pdf2png.Rd
index 8256fae..1ea1aa9 100644
--- a/man/pdf2png.Rd
+++ b/man/pdf2png.Rd
@@ -48,8 +48,9 @@ dpi) PNG files.
   plot(1:5)
   dev.off()
 
+  pngfile <- file.path(tmpdir, "test.png")
   pdf2png(pdffile)
-  pdf2png(pdffile, outfile="test.png")
+  pdf2png(pdffile, outfile=pngfile)
 
   testfile <- system.file("/doc/intro.pdf", package="limma")
   if(file.exists(testfile)) {
diff --git a/vignettes/cascadePlot.Rmd b/vignettes/cascadePlot.Rmd
deleted file mode 100644
index 57dc5df..0000000
--- a/vignettes/cascadePlot.Rmd
+++ /dev/null
@@ -1,65 +0,0 @@
----
-title: "Cascade plot"
-author: "Jitao David Zhang"
-date: "`r Sys.Date()`"
-output: rmarkdown::html_vignette
-vignette: >
-  %\VignetteIndexEntry{Cascade plot in ribiosPlot}
-  %\VignetteEngine{knitr::rmarkdown}
-  %\VignetteEncoding{UTF-8}
----
-
-```{r setup, include = FALSE}
-knitr::opts_chunk$set(
-  collapse = TRUE,
-  comment = "#>"
-)
-```
-
-Vignettes are long form documentation commonly included in packages. Because they are part of the distribution of the package, they need to be as compact as possible. The `html_vignette` output type provides a custom style sheet (and tweaks some options) to ensure that the resulting html is as small as possible. The `html_vignette` format:
-
-- Never uses retina figures
-- Has a smaller default figure size
-- Uses a custom CSS stylesheet instead of the default Twitter Bootstrap style
-
-## Vignette Info
-
-Note the various macros within the `vignette` section of the metadata block above. These are required in order to instruct R how to build the vignette. Note that you should change the `title` field and the `\VignetteIndexEntry` to match the title of your vignette.
-
-## Styles
-
-The `html_vignette` template includes a basic CSS theme. To override this theme you can specify your own CSS in the document metadata as follows:
-
-    output: 
-      rmarkdown::html_vignette:
-        css: mystyles.css
-
-## Figures
-
-The figure sizes have been customised so that you can easily put two images side-by-side. 
-
-```{r, fig.show='hold'}
-plot(1:10)
-plot(10:1)
-```
-
-You can enable figure captions by `fig_caption: yes` in YAML:
-
-    output:
-      rmarkdown::html_vignette:
-        fig_caption: yes
-
-Then you can use the chunk option `fig.cap = "Your figure caption."` in **knitr**.
-
-## More Examples
-
-You can write math expressions, e.g. $Y = X\beta + \epsilon$, footnotes^[A footnote here.], and tables, e.g. using `knitr::kable()`.
-
-```{r, echo=FALSE, results='asis'}
-knitr::kable(head(mtcars, 10))
-```
-
-Also a quote using `>`:
-
-> "He who gives up [code] safety for [code] speed deserves neither."
-([via](https://twitter.com/hadleywickham/status/504368538874703872))