Modeling the atmospheric refractive index structure parameter using macrometeorological observations.

The dynamic fluctuations in the atmospheric refractive index, commonly referred to as optical turbulence, cause phase distortions of the electromagnetic waves propagating through the atmosphere. The consequent scintillations have large implications for free-space optical communication, laser remote sensing, and directed energy applications. The refractive index structure parameter (C n2), quantifying the strength of these fluctuations, is usually estimated using high-frequency micrometeorological measurements, employing sonic anemometer-thermometers or scintillometers. Despite providing highly accurate information, these systems are immensely complex and costly, especially for frequent field applications and remote locations. In this study, we have developed an empirical multinomial model for estimating C n2 using three-year macrometeorological data and validated it against collocated and concurrent micrometeorological measurements, from a tropical semi-arid location. This simpler model would be handy for applications in remote locations having weather station measurements alone.

Enhanced optical pulse broadening in free-space optical links due to the radiative effects of atmospheric aerosols.

Propagation through turbulent media produces complex amplitude fluctuations and temporal spreading of narrow optical pulses. Light-absorbing aerosols present in the atmospheric transmission path will perturb the refractive index structure parameter (Cn2) through atmospheric heating. The consequent enhancement in broadening and attenuation of ultrashort (femtosecond) optical pulses has been calculated by combining multi-satellite observations, radiosonde profiles and computational radiative transfer. It is shown that narrower optical pulses are more vulnerable to aerosol-induced impairments while broader pulses are more resilient, notwithstanding three to four orders of enhanced optical scintillation.

Radiative effects of atmospheric aerosols on the average channel capacity of free-space optical communication systems.

Free-space optical (FSO) communication systems employ unguided light beams propagating through the atmosphere to carry a large volume of data. The reliability of such data transfer can be hampered by various atmospheric effects. Based on an analytical model of a differential phase-shift keying FSO system through exponentiated Weibull turbulence, we investigate the effectiveness of beam width optimization and improved beam alignment, along with aperture averaging on the average channel capacity. Our results show significant signal deterioration produced due to the aerosol-induced optical turbulence, which substantially shadows the performance gain achieved through beam width optimization. Strong aerosol-induced atmospheric heating and the consequent enhanced optical scintillations result in reduction of the channel capacity by as much as 50% of its value when these effects are not considered or negligible. FSO systems are more resilient to aerosol-induced optical turbulence when the normalized beam width is less, and the average channel capacity can be significantly improved by improved beam alignment. These variations are weakly dependent under poor transmitter-receiver alignment conditions. Furthermore, the receiver aperture has a strong control on the link performance. While FSO systems with higher magnitude of normalized beam width have improved performance under all aperture diameter conditions; for a given beam configuration, large aperture diameter ensures a significant improvement in the link performance due to reduction in effects of scintillations.

Entanglement of near-surface optical turbulence to atmospheric boundary layer dynamics and particulate concentration: implications for optical wireless communication systems.

Localized reduction in optical turbulence due to enhanced atmospheric heating caused by the solar absorption of aerosol black carbon (BC) is reported. Immediate response of atmospheric turbulence to BC-induced atmospheric warming strongly depends on the available solar radiation (time of the day), BC concentration, and atmospheric boundary layer dynamics. Besides the significant climate implications of a reduction in turbulence kinetic energy, a large reduction in the refractive index structure parameter (Cn2) resulting from BC-induced warming would affect the atmospheric propagation of laser beams. Interestingly, aerosols contribute significantly (up to 25%) to the signal deterioration in optical wireless communication systems during convectively stable atmospheric conditions when higher signal-to-noise ratios are expected otherwise due to the reduced thermal convection. Competing effects of the fractional contributions of aerosol extinction and scintillations on beam attenuation are reported; daytime being largely dominated by scintillation effects while the nighttime being dependent on the ambient aerosol concentration as well. We put forward the entanglement of optical turbulence to aerosol concentration, atmospheric boundary layer dynamics, and surface-reaching solar radiation, and discuss the possible implications for optical propagation.

Performance of free-space optical communication systems: effect of aerosol-induced lower atmospheric warming.

We report the effect of aerosol-induced local atmospheric heating and the resulting changes in the lower atmospheric optical turbulence on the performance of Free-Space Optical (FSO) communication links. A closed form mathematical expression is derived to estimate the influence of aerosol-induced warming on the Bit Error Rate (BER) of a Binary Phase Shift Keying FSO communication link through Gamma-Gamma modeled turbulence. Our results demonstrate a strong impact, with the aerosol-induced turbulence taking a toll on the signal-to-noise ratio of ~20 dB for a BER of 10-9. Aerosol-induced warming produces significant variations in BER compared to the clear atmospheric conditions and can subdue the benefits of improved beam alignment.

Dependence of atmospheric refractive index structure parameter (Cn2) on the residence time and vertical distribution of aerosols.

Effects of absorbing atmospheric aerosols in modulating the tropospheric refractive index structure parameter (Cn2) are estimated using high resolution radiosonde and multi-satellite data along with a radiative transfer model. We report the influence of variations in residence time and vertical distribution of aerosols in modulating Cn2 and why the aerosol induced atmospheric heating needs to be considered while estimating a free space optical communication link budget. The results show that performance of the link is seriously affected if large concentrations of absorbing aerosols reside for a long time in the atmospheric path.

From microscopy centre to culture laboratory: a viable ride for mycobacteria.

SETTINGS: Culture and drug susceptibility testing of Mycobacterium tuberculosis is required for the treatment of drug-resistant tuberculosis. Cetylpyridinium chloride-sodium chloride (CPC-NaCl) solution is recommended for the preservation of sputum during transport. OBJECTIVE: To study the possibility of sputum preservation and transport in CPC-NaCl and its effect on culture. DESIGN: Sputum specimens preserved with CPC-NaCl were transported to the laboratory for culture from remote microscopy centres of Andhra Pradesh and Orissa states, India. RESULTS: Of the 175 specimens, 140 (80%) yielded mycobacteria, 21 (12%) did not yield any growth, 11 (6.2%) grew contaminants and 3 (1.7%) were lost due to leakage. Culture positivity was greater in specimens stored for 1 week. Culture results from specimens stored for 2 weeks are encouraging. CONCLUSION: The CPC-NaCl preservation technique can be used for effective preservation and transport of

Supravalvar aortic stenosis: clinical and hemodynamic profile, and surgical outcome.

BACKGROUND: Supravalvar aortic stenosis is the rarest of left ventricular outflow obstructions. Data on this rare entity from India are scarce. METHODS AND RESULTS: We retrospectively analyzed the data of 15 patients (13 males, mean age 15.5+/-10.18 years) with a diagnosis of supravalvar aortic stenosis confirmed by cardiac catheterization. Five patients had morphological features of Williams' syndrome. One patient had diffuse while the rest had discrete type of supravalvar aortic stenosis. Five patients did not have any associated lesions. A 9-year-old male had an ascending aortic aneurysm, and 3 patients had associated peripheral pulmonary artery stenosis. One child had a subaortic ventricular septal defect, and another had severe mitral regurgitation. Twelve patients had electrocardiographic evidence of left ventricular hypertrophy. Three patients had mild aortic valvar stenosis while 2 had aortic regurgitation. Six patients had dilated coronary arteries. Two patients with supravalvar aortic gradients of 20 and 40 mmHg were kept on close follow-up. One patient was not willing to undergo surgery while the other is awaiting surgery. Eleven patients underwent surgical correction. Dacron or pericardial patch aortoplasty was done in all the patients. In addition, one patient each underwent pulmonary artery plasty, ventricular septal defect closure, repair of ascending aortic aneurysm, and mitral valve replacement. The patient with diffuse type of supravalvar aortic stenosis underwent augmentation aortoplasty. Two patients died perioperatively. One was lost to follow-up. Two had moderate residual gradients. The rest of the patients were in New York Heart Association functional class I on follow-up of 6.3+/-4.7 years. CONCLUSIONS: Repair of supravalvar aortic stenosis by single sinus aortoplasty is safe and produces good results.

Relapse of leprosy presenting as nodular lymph node swelling.

Lymphadenopathy is known to be associated with lepromatous leprosy and has also been observed as a feature of type-2 lepra reaction. However, nodular lymph node enlargement is not commonly reported in leprosy patients or as a feature of relapse. We herewith are presenting a case of bacteriological relapse in a patient of lepromatous leprosy treated 22 years before till smear negativity with WHO multidrug therapy (MDT) multibacillary type (MB). She presented with prominent nodular swelling of the cervical group of lymph nodes along with generalized lymphadenopathy, which was mistakenly treated as tubercular lymphadenopathy. A diagnosis of late bacteriological relapse of lepromatous leprosy presenting with prominent lymphadenopathy and ENL was made after relevant investigations. The patient was started on treatment with WHO MDT MB (daily dapsone and clofazimine and monthly rifampicin) and thalidomide (200 mg/day). Nerve pain regressed within 2 weeks of therapy. The lymph nodal swelling regressed within 3 months of starting treatment.

Mycobacterial culture of fine needle aspirate - a useful tool in diagnosing tuberculous lymphadenitis.

A prospective study was undertaken on suspected lymph node TB (LNTB) patients, to evaluate the diagnostic utility of mycobacterial culture of fine needle aspirate (FNA), in comparison with the cytological examination and acid fast staining. Eighty percent of 157 aspirates studied were positive by cytological examination; 18% by ZN smear and 45% were positive by culture. Twelve aspirates which were negative by cytological features yielded positive mycobacterial cultures; four out of these were from HIV positive patients. Our observations suggest that supplementing FNA cytology with mycobacterial culture would increase the sensitivity of diagnosing LNTB; in addition to giving a highly specific diagnosis.