fix sciencedirect links

Author: nvaytet

docs/user-guide/tof/wfm.ipynb

@@ -8,7 +8,7 @@
     "# Wavelength frame multiplication\n",
     "\n",
     "Wavelength frame multiplication (WFM) is a technique commonly used at long-pulse facilities to improve the resolution of the results measured at the neutron detectors.\n",
-    "See for example the article by [Schmakat et al. (2020)](https://www.sciencedirect.com/science/article/pii/S0168900220308640) for a description of how WFM works.\n",
+    "See for example the article by [Schmakat et al. (2020)](https://doi.org/10.1016/j.nima.2020.164467) for a description of how WFM works.\n",
     "\n",
     "In this notebook, we show how to use `essreduce`'s `time_of_flight` module to compute an accurate a time-of-flight coordinate,\n",
     "from which a wavelength can be computed."
@@ -41,7 +41,7 @@
     "We begin by defining the chopper settings for our beamline.\n",
     "In principle, the chopper setting could simply be read from a NeXus file.\n",
     "\n",
-    "For this example, we create choppers modeled on the [V20 ESS beamline at HZB](https://www.sciencedirect.com/science/article/pii/S0168900216309597).\n",
+    "For this example, we create choppers modeled on the [V20 ESS beamline at HZB](https://doi.org/10.1016/j.nima.2016.09.034).\n",
     "It consists of 5 choppers:\n",
     "\n",
     "- 2 WFM choppers\n",

src/ess/reduce/time_of_flight/toa_to_tof.py

@@ -82,6 +82,7 @@ def compute_tof_lookup_table(
     """
     Compute a lookup table for time-of-flight as a function of distance and
     time-of-arrival.
+
     Parameters
     ----------
     simulation:
@@ -342,6 +343,7 @@ def time_of_flight_data(
     """
     Convert the time-of-arrival data to time-of-flight data using a lookup table.
     The output data will have a time-of-flight coordinate.
+
     Parameters
     ----------
     da: