diff --git a/README.md b/README.md
index 3cc7e85..b2eca9d 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,9 @@
-# MUDA-based Solid Simulatoion Tutorial
-This is a tutorial for Solid Simulations using [MUDA](https://github.com/MuGdxy/muda) (a CUDA programming paradigm).
+# MUDA-based Solid Simulation Tutorial
+This is a tutorial for elastodynamic contact simulation using [MUDA](https://github.com/MuGdxy/muda) (a [CUDA](https://developer.nvidia.com/cuda-toolkit) programming paradigm).
 
-The basic architecture of the simulators follows [@liminchen](https://github.com/liminchen)'s Numpy version [Solid-Sim-Tutorial](https://github.com/phys-sim-book/solid-sim-tutorial).
+The basic architecture of the simulators follows [@liminchen](https://github.com/liminchen)'s Numpy version [solid-sim-tutorial](https://github.com/phys-sim-book/solid-sim-tutorial).
 
-The tutorial (written by a beginner of simulation) aims at helping beginners learn how to write simple CUDA codes for efficient solid simulation on the GPU.
+The tutorial (written by a beginner of simulation) aims at helping beginners learn how to write simple CUDA codes for efficient solid simulations on the GPU. An introductory section for the first example of this tutorial can be found at [https://phys-sim-book.github.io/lec4.6-gpu_accel.html](https://phys-sim-book.github.io/lec4.6-gpu_accel.html).
 
 ## Usage
 1. Clone the repository
diff --git a/simulators/8_self_friction/src/FrictionEnergy.cu b/simulators/8_self_friction/src/FrictionEnergy.cu
index 60c2932..8ca5f3a 100644
--- a/simulators/8_self_friction/src/FrictionEnergy.cu
+++ b/simulators/8_self_friction/src/FrictionEnergy.cu
@@ -11,7 +11,7 @@ template <typename T, int dim>
 struct FrictionEnergy<T, dim>::Impl
 {
     DeviceBuffer<T> device_v;
-    DeviceBuffer<T> device_mu_lambda，device_mu_lambda_self，device_r_self;
+    DeviceBuffer<T> device_mu_lambda, device_mu_lambda_self, device_r_self;
     DeviceBuffer<T> device_grad;
     DeviceBuffer<int> device_bp, device_be;
     DeviceBuffer<Eigen::Matrix<T, 2, 1>> device_n_self;