Numerical study on THz radiation of two-dimensional plasmon resonance of GaN HEMT array

The Ga N high electron mobility transistor(HEMT)has been considered as a potential terahertz(THz)radiation source,yet the low radiation power level restricts their applications.The HEMT array is thought to improve the coupling efficiency between two-dimensional(2D)plasmons and THz radiation.In this work,we investigate the plasma oscillation,electromagnetic radiation,and the integration characteristics of Ga N HEMT targeting at a high THz radiation power source.The quantitative radiation power and directivity are obtained for integrated Ga N HEMT array with different array periods and element numbers.With the same initial plasma oscillation phase among the HEMT units,the radiation power of the two-element HEMT array can achieve 4 times as the single HEMT radiation power when the array period is shorter than 1/8electromagnetic wavelength.In addition,the radiation power of the HEMT array varies almost linearly with the element number,the smaller array period can lead to the greater radiation power.It shows that increasing the array period could narrow the main radiated lobe width while weaken the radiation power.Increasing the element number can improve both the radiation directivity and power.We also synchronize the plasma wave phases in the HEMT array by adopting an external Gaussian plane wave with central frequency the same as the plasmon resonant frequency,which solves the problem of the radiation power reduction caused by the asynchronous plasma oscillation phases among the elements.The study of the radiation power amplification of the one-dimensional(1D)Ga N HEMT array provides useful guidance for the research of compact high-power solid-state terahertz sources.

Improvement of left ventricular function in patients with persistent atrial tachyarrhythmia induced cardiomyopathy undergoing radiofrequency ablation

Purpose: To investigate the alteration of left ventricular function in subjects with persistent atrial tachyarrhythmia induced cardiomyopathy (TIC) undergoing radiofrequency ablation, and to study the pathogenesis and effective treatment of TIC. Methods: A total of 25 cases with persistent atrial tachyarrhythmia and impaired left ventricular systolic function were studied (16 men and 9 women, aged 53.3 ± 15.2 years), and all subjects underwent electrophysiological study and radiofrequency ablation of atrial tachyarrhythmia under the guidance of CARTO system during 2006.9-2011.8. Indexes related to cardiac function, including left ventricular end diastolic diameter (LVEDD), left ventricular ejection fraction (LVEF), New York Heart Association functional classification (NYHA class), 6 minutes walking test (6MWT), N-terminal pro-brain natriuretic peptide (BNP) and 24 hours average heart rate (AHR), were analyzed at the time point of 7 days, 3 and 6 months after the procedure as well as 1 day before ablation. Results: No refractory atrial arrhythmia recurred in all cases after ablation, compared with LVEDD (51.7 ± 4.5 mm), LVEF (39.0% ± 4.3%), number of patients with NYHA class IV and III (n = 17), 6MWT (212 ± 56 m), BNP (3622 ± 1860 ng/L) and AHR (112.5 ± 23.2 bpm) before ablation, the index of LVEDD (45.2 ± 3.3 mm;41.7 ± 2.5 mm;40.5 ± 3.1 m), BNP (2429 ± 1355 ng/L;1530 ± 866 ng/L;1300 ± 520 ng/L), total number of patients of NYHA class IV and III (n = 11;3;2) and AHR (73.3 ± 15.3 bpm;68.7 ± 13.5 bpm;66.3 ± 13.6 bpm) significantly decreased (P < 0.05), LVEF (45.6 ± 3.5%;51.5 ± 2.7%;53.5 ± 3.1%) and 6MWT (262 ± 47 m;305 ± 37 m;313 ± 41 m) greatly increased (P < 0.05)in 7 days, 3 and 6 months after ablation respectively. There was a statistical difference between 7 days and 3 or 6 months after ablation in above-mentioned indexes (P < 0.05) except AHR (P > 0.05), no significant difference existed between 3 and 6 months in all indexes (P > 0.05). Conclusion: long-lasting atrial arrhythmia with rapid ventricular response could impair left ventricle function, which could be reversed within weeks after successful ablation and restoration of sinus rhythm.