```ruby
class UsersController < ApplicationController
  layout "channels"

  before_filter :load_user

  def show
    respond_to do |format|
      format.html { redirect_to(channel_path(params[:username], @user.graph_user.stream)) }
      format.json { render json: {"user" => Users::User.for(user: @user, view: view_context) }}
    end
  end

  def activities
    respond_to do |format|

      # TODO: This needs to become much more efficient. Now all activities are
      # returned and sliced.
      activities = Activity::For.user(current_user.graph_user).sort(order: "DESC").slice(0..6)

      format.json { render json: activities.map { |activity| Notifications::Activity.for(activity: activity, view: view_context) } }
    end
  end

  def mark_activities_as_read
    current_user.last_read_activities_on = DateTime.now

    respond_to do |format|
      if current_user.save
        format.json { head :no_content }
      else
        format.json { render json: { :status => :unprocessable_entity } }
      end
    end
  end

  private
  def load_user
    @user = User.first(:conditions => { :username => params[:username] }) or raise_404
  end
end
```

Use @user instead of current_user
user
```ruby
class UsersController < ApplicationController
  layout "channels"

  before_filter :load_user

  def show
    respond_to do |format|
      format.html { redirect_to(channel_path(params[:username], @user.graph_user.stream)) }
      format.json { render json: {"user" => Users::User.for(user: @user, view: view_context) }}
    end
  end

  def activities
    respond_to do |format|
    # TODO: This needs to become much more efficient. Now all activities are
    # returned and sliced.
    activities = Activity::For.user(@user.graph_user).sort(order: "DESC").slice(0..6)


      format.json { render json: activities.map { |activity| Notifications::Activity.for(activity: activity, view: view_context) } }
    end
  end

  def mark_activities_as_read
    @user.last_read_activities_on = DateTime.now

    respond_to do |format|
      if current_user.save
        format.json { head :no_content }
      else
        format.json { render json: { :status => :unprocessable_entity } }
      end
    end
  end

  private
  def load_user
    @user = User.first(:conditions => { :username => params[:username] }) or raise_404
  end
end
```
assistant