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.

Maternal and fetal vascular lesions of malperfusion in the placentas associated with fetal and neonatal death: results of a prospective observational study.

BACKGROUND: Fetal death is one of the major adverse pregnancy outcomes and is common in low- and middle-income countries. Placental lesions may play an important role in the etiology of fetal and neonatal deaths. Previous research relating placental lesions to fetal death causation was hindered by a lack of agreement on a placental classification scheme. The Amsterdam consensus statement that was published in 2016 focused its attention on malperfusions in the maternal and fetal placental circulations. OBJECTIVE: This study aimed to investigate the relationships of placental maternal and fetal vascular malperfusions in fetal and neonatal deaths, focusing on the most important maternal clinical conditions in the pathway to fetal and neonatal deaths, such as maternal hypertension, antepartum hemorrhage, and decreased fetal growth. STUDY DESIGN: This was a prospective, observational cohort study conducted at 2 Asian sites. The data collected included clinical history, gross and histologic evaluations of the placenta, and several other investigations and were used to determine the cause of death. The placenta was evaluated at both sites using the Amsterdam consensus framework. We estimated the risk of placental maternal and fetal vascular malperfusions in fetal and neonatal deaths. RESULTS: Between July 2018 and January 2020 in India and Pakistan, 1633 women with placentas available for the study provided consent. Of these women, 814 had fetal deaths, 618 had preterm live births and subsequent neonatal deaths, and 201 had term live births. The prevalence of maternal vascular malperfusion was higher in the placentas associated with fetal deaths (58.4%) and preterm neonatal deaths (31.1%) than in the placentas associated with term live births (15.4%). Adjusting for site, maternal vascular malperfusion had a relative risk of 3.88 (95% confidence interval, 2.70-5.59) in fetal deaths vs term live births and a relative risk of 2.07 (95% confidence interval, 1.41-3.02) in preterm neonatal deaths vs term live births. Infarcts and distal villous hypoplasia were the most common histologic components of maternal vascular malperfusion. Compared with maternal vascular malperfusion (58.4%), fetal vascular malperfusion was less common in the placentas associated with fetal deaths (19.0%). However, there were higher frequencies of fetal vascular malperfusion in the placentas associated with fetal deaths (19.0%) than in placentas associated with neonatal deaths (8.3%) or term live birth (5.0%). Adjusting for site, fetal vascular malperfusion had a relative risk of 4.09 (95% confidence interval, 2.15-7.75) in fetal deaths vs term live births and a relative risk of 1.77 (95% confidence interval, 0.90-3.49) in preterm neonatal deaths vs term live births. Furthermore, there was a higher incidence of maternal vascular malperfusion in cases of maternal hypertension (71.4%), small for gestational age (69.9%), and antepartum hemorrhage (59.1%) than in cases of fetal deaths with none of these conditions (43.3%). There was no significant difference in the occurrence of fetal vascular malperfusion in the 4 clinical categories. CONCLUSION: Histologic examination of the placenta, especially for malperfusion disorders, is crucial in elucidating pathways to fetal and neonatal deaths in preterm infants. In particular, focusing on placental maternal and fetal vascular malperfusions during pregnancy is a means to identify fetuses at risk of fetal death and is an important strategy to reduce the risk of fetal death early delivery. We hope that the increased risk of fetal and neonatal deaths in these pregnancies can be reduced by the development of an intervention that reduces the likelihood of developing maternal and fetal vascular malperfusion.

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.

Distinctive roles of elevated absorbing aerosol layers on free-space optical communication systems.

The impact of enhanced local heating due to absorption of solar radiation by elevated layers of aerosol black carbon (BC) in the lower troposphere in the performance of free-space optical (FSO) communication links is investigated. It is seen that a strong elevated BC layer at an altitude around 4.5 km enhances the atmospheric stability locally and leads to a large reduction in the atmospheric refractive index structure parameter (Cn2), leading to improved performance of the FSO communication links. For layers in the tropical atmosphere with sufficiently high BC concentration, the signal attenuation due to BC absorption is alleviated by the large reduction in Cn2 due to BC-induced warming and brings down the link outage probability. Synergy between reduction in Cn2 and long wavelength transmission improves the link budget significantly by reducing the beam wander and number of adaptive optics units required.

Collagenofibrotic glomerulopathy: A case of glomerular deposition disease in the Indian subcontinent and review of the literature.

Collagenofibrotic glomerulopathy (CG) is a rare renal disease with unknown etiology, defined by deposition of Type III collagen fibers in the subendothelial space and mesangium seen on supported by electron microscopy. There are merely 19 cases reported in the literature from the Indian subcontinent. Herein, we present a case report of CG from the Indian subcontinent and review its literature mainly focusing on histopathological findings.

Randomized controlled trial of DOTS versus conventional regime for treatment of ileocecal and colonic tuberculosis.

There is limited information regarding the efficacy of 'directly observed treatment short course' (DOTS) in the treatment of intestinal tuberculosis. We randomized patients with ileocecal or colonic tuberculosis to receive daily tuberculosis chemotherapy (Group A) or DOTS (Group B). Patients received isoniazid, rifampicin, pyrazinamide and ethambutol daily for two months in group A and thrice weekly for 2 months in group B, followed by isoniazid and rifampicin daily for 7 months in group A and thrice weekly for 4 months in group B. Patients were followed up at 2 and 4 weeks and monthly thereafter until the end of treatment. Follow up colonoscopy was done at 2 and 6 months after starting treatment. The improvement in clinical symptoms was not different between Groups A (24) and B (23) at 2 and 6 months. Mean increase in weight was 5.1 (0.5) Kg and 5.7 (0.6) Kg at 2 months and 7.1 (1.7) Kg and 6.9 (1.9) Kg at 6 months in Group A and B, respectively. Complete healing of ulceration was noted in 75% of Group A patients and 79% of Group B patients at 2 months and in all patients in both groups at 6 months. We conclude that DOTS and daily chemotherapy are equally effective for treating ileocecal and colonic tuberculosis.

Profile of colonic polyps in a southern Indian population.

BACKGROUND: In Western countries, colonic polyps are usually adenomatous in nature, are evenly distributed along the entire colon in asymptomatic per-sons and show a left-sided predominance in symptomatic patients. There is dearth of such literature from India. METHODS: We retrospectively analyzed reports of colonoscopies done in our institution during the period 2001 to 2005. Clinical features, colonoscopic description and histologic findings of all patients with polyps were noted. Association of the degree of dysplasia with the size, site and type of polyps and the person's age was assessed. RESULTS: Polyps were seen in 124 (5.1%) of 2412 complete colonoscopies. Mean age of patients with polyps was 58.1 (SD 19.9) years; ninety were men. A majority of polyps (92%) were located in the left colon. They were adenomatous in 99 (79.8%), juvenile in 12 (9.8%), hyperplastic in 11 (8.8 %), inflammatory in 1 (0.8%) and Peutz-Jegher's polyp in 1 (0.8%). Dysplasia was severe in large (>2 cm) polyps compared to small (< 1 cm) ones (p< 0.001). Age of patient and location of polyp had no association with degree of dysplasia. CONCLUSIONS: In southern Indian adults, most colonic polyps are adenomatous and are in the left colon. Large polyps are associated with severe dysplasia.

Endoscopic abnormalities in the oesophagus after variceal sclerotherapy--a long-term follow up study.

Endoscopic sclerotherapy is a well-established treatment modality for oesophageal varices. Various local, regional and systemic complications occur after sclerotherapy. Altered endoscopic appearances of the oesophagus have been observed on follow-up of patients after sclerotherapy. 171 consecutive patients with extra-hepatic portal venous obstruction on follow up after achieving variceal eradication by sclerotherapy during the period from January 2004 to June 2005 were enrolled in this study. The oesophagus was closely observed for mucosal abnormalities and the endoscopic findings were recorded. Out of 171 patients, 95 (55.5%) patients had no specific endoscopic changes in the oesophagus. The most common finding was mucosal neovascularization which was seen in 56 (32.7%) patients. Oval or oblong depressed areas were seen in 41 (23.9%) patients. Mucosal tags and polypoidal lesions were seen in 37 (21.6%) patients. 25 (15.6%) patients had stenosis of the lower oesophagus and 3 (1.7%) patients had mucosal bridges. On multivariate analysis, these abnormal endoscopic findings in the oesophagus correlated with the total volume of sclerosant injected when compared with those patients without similar findings on endoscopy (p value < 0.001). Endoscopic sclerotherapy leads to various abnormalities at the injection sites like neovascularization, oval or oblong depressed areas, mucosal tags, polypoidal lesions, stenosis and mucosal bridges. Endoscopic abnormalities correlated with the total volume of sclerosant used. The long-term significance of these changes is not known at present and further follow-up studies will be required.

External resection of a giant sigmoid lipoma causing colonic intussusception and prolapse through the anal canal.

We depict the case of an 80-year-old female patient who presented to us with a history of protruding mass per anum. Sigmoidoscopy revealed a large globular pedunculated polyp at 22 cm from the anal verge resulting in a sigmoidorectal intussusception. Endoscopic polypectomy was not technically possible due to the large size of the polyp. At the time of prolapse the polyp was tied at its pedicle with thread and resected surgically. The patient is asymptomatic on follow-up.

Non-familial juvenile polyposis in prolapsed rectum.

Juvenile polyposis located solely on prolapsed rectal mucosa is very unusual. We report the case of a 17-year old boy who presented to us with a history of passage of blood and mucus per rectum of a mass protruding through the anus during defecation. Per rectal and colonoscopic examinations revealed numerous polyps located solely on the prolapsed rectal mucosa. Histopathology was consistent with juvenile polyposis. He was managed with repeated sessions of endoscopic polypectomy. Family screening was negative for colonic polyps.

Abrikosoff's tumor of the esophagus: case report and review of literature.

Abrikosoff's tumor or granular cell tumor is a neoplasm of neural origin, usually located in the head and neck region. A majority of these neoplasms are benign. Only 4-6% of granular cell tumors are located in the gastrointestinal tract. It is extremely unusual for these tumors to be located in the esophagus. This case is being reported in view of the rarity of this lesion. A brief review of literature with stress on diagnostic evaluation and management issues is also included.

Prevalence of Hepatitis B and C in the normal population and high risk groups in north Kerala.

BACKGROUND: Our aim is to assess the prevalence of Hepatitis B and Hepatitis C infections among normal healthy persons and high risk groups in the northern part of Kerala state in South India as there is insufficient published literature related to this subject. METHODS: HBsAg and AntiHCV screening were done in normal persons and in high risk groups. Normal persons screened included voluntary blood donors, those attending mandatory medical check up for jobs in middle east Asia and pregnant women. High risk groups were health care workers, intravenous drug abusers, commercial sex workers and male homosexuals. RESULTS: HBsAg and anti HCV antibody test results in the various groups were as follows. Voluntary blood donors--HBsAg was positive in 0.71 % and anti HCV was positive in 0.33%; job seekers to middle east Asia had 0.89% and 0.12% prevalence of HBV and HCV respectively. Among the pregnant women, 0.21% were HBsAg positive. Among the high risk groups, none of the health care workers were HbsAg positive and 0.79% were antiHCV positive. Among the IV drug abusers 2.7% were HBsAg positive and 51.89% were positive for antiHCV. In commercial sex workers, 3.47 % were HBsAg positive and 2.6 % were antiHCV positive. In male homosexuals, 4.49% were HBsAg positive and 3.37% were antiHCV positive. CONCLUSIONS: The prevalence of Hepatitis B and C in the normal population of Calicut in the northern part of Kerela is 0.52% and 0.24%. Compared to other areas of India, the seroprevalence of Hepatitis B and C are low in the normal population of Calicut. Among the high-risk groups, IV drug users have a high prevalence of AntiHCV.

Reproducibility and validity of oral visual inspection by trained health workers in the detection of oral precancer and cancer.

A randomized intervention trial is in progress in Kerala, India, to evaluate the effectiveness of oral visual inspection by trained health workers (HWs) in the prevention of oral cancer. Fourteen health workers with college graduation as the basic qualification were trained in oral visual inspection to identify oral cancers and precancers among the participants of the screening trial and to refer them for further confirmation and management. The aim of the present study was to evaluate the reproducibility and validity of the screening test provided by the health worker against the reference oral visual findings of three physicians. A total of 2069 subjects who had already been examined were re-examined by the health workers and physicians. The sensitivity and the specificity of the oral visual inspection were 94.3% and 99.3% respectively. There was moderate agreement between the findings of the initial and the repeat mouth examinations carried out by the health workers, which were on average 6 months apart. There was almost perfect agreement (kappa = 0.85) between the findings of the health workers and the physicians in identifying the different types of oral precancerous lesions. The findings of our study indicate that it is possible to train resource persons to perform the oral cancer screening test as accurately as doctors, although experience appears to be a crucial component of health workers' accuracy. The efficacy of such an approach to reduce the incidence of and mortality from oral cancer, however, remains to be proven.