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To explore the vibration transmission characteristics and vibration reduction effects of metro tunnels with different track structures, the regular slab track section, the double-layer nonlinear vibration-damping fastener section and the isolated damping pad section in the Nanchang Metro Line 3 were selected respectively for the field hammer excitation test. Based on the field test results, the vibration transmission characteristics and the vibration reduction effects of metro tunnels with different track structures were analyzed. The results indicated that the vibration reduction effect of the isolated damping pads was best, followed by the double-layer nonlinear vibration-damping fasteners, while that of the regular slab tracks was worst; the double-layer nonlinear vibration-damping fastener section had obvious vibration reduction effect in the frequency range of 80 to 170 Hz, the isolated damping pad section had significant vibration reduction performance above 30 Hz; the vibration of the double-layer nonlinear vibration-damping fastener section and the isolated damping pad section was 5.6 dB and 10 dB less than the regular slab track section, respectively.

A 37-year-old man was admitted to our cardiology department with sustained palpitations for 36 hours. He had suffered from paroxysmal palpitations for five years. This had happened one to three times per month, especially in the six months before admission and syncope occurred occasionally. The most useful way to terminate the acute episode of palpitations was a loading dose of propafenone (up to 210 mg). The patient had been diagnosed with dilated cardiomyopathy seven years ago by an ultrasound examination. The onset electrocardiogram (ECG) was a fast and regular rhythm with wide QRS complexes (174 beats/min). During the administration of propafenone, the following ECG was documented (figure 1). What is your diagnosis?