The number of atomic or molecular collisions with a wall of a container per unit area per unit time (impingement rate) is given by:

assuming mean free path is much greater than pinhole diameter and the gas can be treated as an ideal gas.If a small area 
  
    
      
        A
      
    
    {\displaystyle A}
   on the container is punched to become a small hole, the effusive flow rate will be

where 
  
    
      
        M
      
    
    {\displaystyle M}
   is the molar mass, 
  
    
      
        
          N
          
            A
          
        
      
    
    {\displaystyle N_{A}}
   is the Avogadro constant, and 
  
    
      
        R
        =
        
          N
          
            A
          
        
        
          k
          
            B
          
        
      
    
    {\displaystyle R=N_{A}k_{B}}
   is the gas constant.
Microscopically, AAH is a well-demarcated focus of epithelial proliferation, containing cuboidal to low-columnar cells resembling club cells or type II pneumocytes. These demonstrate various degrees of cytologic atypia, including hyperchromasia, pleomorphism, prominent nucleoli. However, the atypia is not to the extent as seen in frank adenocarcinomas. Lesions of AAH are monoclonal, and they share many of the molecular aberrations (like KRAS mutations) that are associated with adenocarcinomas.Signet ring and clear cell adenocarcinoma are no longer histological subtypes, but rather cytological features that can occur in tumour cells of multiple histological subtypes, most often solid adenocarcinoma. Treatment
The treatment of adenocarcinoma of the lung depends on several factors including stage, resectability, performance status, histology and genomic alterations acquired by the individual tumor. As in most cancer types, treatment approaches can be broadly divided into 5 categories: surgery, chemotherapy, radiotherapy, targeted therapy and immunotherapy. Surgery
Early stage (I, II and IIIA) lung adenocarcinomas are typically treated surgically to remove the tumor with pneumonectomy or lobectomy, if it is found to be resectable with imaging studies and biopsies and if the patient is considered able to tolerate surgery. Video-assisted thorascopic surgery (VATS) is often adopted, which consists in the insertion of a thorascope inside a small incision made in the chest; a lobe can be removed via the scope through this small incision. Chemotherapy
For advanced (stage IV) and unresectable lung tumors, the first-line therapy is platinum-based doublet chemotherapy, combining cisplatin or carboplatin with another cytotoxic agent.