concern.rb

# coding: utf-8
class Concern < ActiveRecord::Base
  belongs_to :publication
end

index.html.haml

- @publications.each do |pub|
  = pub.concerns.size
  = pub.publication_comments.size

publication.rb

# coding: utf-8
class Publication < ActiveRecord::Base
  has_many :concerns
  has_many :publication_comments
end

publication_comment.rb

# coding: utf-8
class PublicationComment < ActiveRecord::Base
  belongs_to :publication
end

publications_controller.rb

# coding: utf-8
class PublicationsController < ApplicationController
  def index
    @publications = Publication.all(:include => [:concerns, :publication_comments])
  end
end