A 55-year-old man is brought to the emergency department 45 minutes after he collapsed at home. His pulse is 120/min, respirations are 16/min, and blood pressure is 80/45 mmHg. Physical examination shows no other abnormalities. His hemoglobin concentration is 8g/dL, hematocrit is 24%, and platelet count is 240,000/mm3. Endoscopy shows a bleeding duodenal ulcer, which is surgically repaired. He receives 4 units of packed red blood cells. Two days later, laboratory studies show:Hemoglobin 10 g/dLHematocrit 30%SERUMUrea nitrogen 70 mg/dLCreatinine 3 mg/dLURINEBlood absentSediment granular castsVolume 100 m1124 hTotal protein 100 mg/24 hSodium 50 mEq/LFractional excretion of sodium 2.5%Osmolality 300 mOsmol/kg H20Two weeks later, the urine sediment is clear and renal function is normal. Histologic examination of a renal biopsy specimen is most likely to show which of the following at this time?