Characteristics of energetic motions in turbulent boundary layers

© 2019 Dr. Dileep Chandran Padinjare MuttikkalIn this dissertation, we present the first measurements of two-dimensional (2-D) energy spectra of the streamwise velocity component (u) in high Reynolds number turbulent boundary layers. The measurements in the logarithmic region of turbulent boundary layers give new evidence supporting the self-similarity arguments that are based on Townsend’s (1976) attached eddy hypothesis. The 2-D spectrum is found to be able to isolate the range of self-similar scales from the broadband turbulence, which is not possible with the measurement of a 1-D energy spectrum alone. High Reynolds number flows are characterized by large separation of scales. Therefore, to obtain converged 2-D statistics while resolving the broad spectrum of length and time scales, a novel experimental technique is required. To this end, we devise a technique employing multiple hot-wire probes to measure the 2-D energy spectra of u. Taylor’s frozen turbulence hypothesis is used to convert temporal-spanwise information into a 2-D spatial spectrum which shows the contribution of streamwise (λx) and spanwise (λy) length scales to the streamwise variance at a given wall height (z). The validation of the measurement technique is performed at low Reynolds number by comparing against the direct numerical simulation (DNS) data of Sillero et al. (2014). Based on these comparisons, a correction is introduced to account for the spatial resolution associated with the initial separation of the hot-wires. The proposed measurement technique is used to measure the 2-D spectra in the logarithmic region for friction Reynolds numbers ranging from 2400 to 26000. At low Reynolds numbers, the shape of the 2-D spectra at a constant energy level shows λy/z ∼ (λx/z)1/2 behaviour at large scales, which is in agreement with the existing literature. However, at high Reynolds numbers, it is observed that the square-root relationship tends towards a linear relationship (λy ∼ λx) as required for self-similarity and predicted by the attached eddy hypothesis. Finally, we present a model for the logarithmic region of turbulent boundary layers, which is based on the attached eddy framework and driven by the scaling of experimental 2-D spectra of u. The conventional attached eddy model (AEM), which comprises self-similar wall-attached eddies (Type A) alone, represent the large scale motions at high Reynolds numbers reasonably well. However, the scales that are not represented by the conventional AEM are observed to carry a significant proportion of the total kinetic energy. Therefore, in the present study we propose an extended AEM, where in addition to Type A eddies, we also incorporate Type CA and Type SS eddies. These represent the self-similar but wall-detached low-Reynolds number features and the non-self-similar wall-attached superstructures, respectively. The extended AEM is observed to predict a greater range of energetic length scales and capture the low- and high-Reynolds number scaling trends in the 2-D spectra of all three velocity components

Changes in mortality and human longevity in Kerala: are they leading to the advanced stage?

Background: During the last century, Kerala witnessed drastic mortality reduction and high improvement in longevity. This achievement is often compared with that of developed countries. However, how far the early advantages in mortality reduction have further enhanced in Kerala remains unknown. In most developed countries, advanced stage of mortality reduction and further increase in longevity was achieved mainly due to the mortality shift from adult and older ages to oldest ages (Olshansky and Ault 1986). Objectives: Considering the lack of comprehensive study on the change in longevity in Kerala, this study focuses on discovering (i) the historical time-periods that provided the biggest gain to life expectancy and also the beneficiaries (by age group and sex) and (ii) the contributions of major groups of causes of death in mortality reduction and consequent improvement in longevity. Methodology and data: The study uses the methodology proposed by Olshansky and Ault in 1986. It used methods such as Temporary Life Expectancy (TLE), Annual Relative Change in TLE, Decomposition of changes in longevity among different age groups (gender and spatial) and causes of deaths, for the analysis. It used data from various sources such as Census, Civil Registration System (CRS) and Directorate of Health Services (DHS), as well as survey data from Sample Registration System (SRS) and Medically Certified Causes of Deaths (MCCD) for this study. Finding and conclusion: The study found that overall mortality dramatically declined in the state in the recent decades. Younger ages have contributed the most for this reduction. Therefore, further mortality reduction is possible in adult and early old ages. However, the contribution of these ages to life expectancy was lower than that of youngsters until 1991–2000 especially among males. This may indicate a slow progress towards the advanced stage of epidemiological transition characterized by high prevalence of non-communicable diseases. The paper concludes that although the health issues of infants, children, and mothers in the reproductive age group, are effectively addressed through various policies in Kerala, the state needs to focus more on the health problems of adults, especially males

Congenital X-linked Stapes Gusher Syndrome in an Infant A Case Report

Congenital X-linked deafness with stapes gusher is a rare, but well-known clinical entity with characteristic radiological features. Recognition of these findings is important as it changes the treatment course and precludes stapedectomy, which if done can lead to stapes gusher in these patients. We present the case of a nine-month-old male infant with hearing loss. CT scan showed typical radiological features of X-linked stapes gusher syndrome. In addition, the superior semicircular canals appeared dehiscent which could be due to immature ossification or less likely due to defective development as part of the disease. To the best of our knowledge this is the youngest patient prospectively identified by imaging in the English medical literature

Spontaneous regression and recurrence of a tumefactive perivascular space

Perivascular spaces can occasionally appear mass-like (tumefactive or giant perivascular space), and can be associated with clinical symptoms. Spontaneous regression of a tumefactive perivascular space is a very rare phenomenon with only two reported cases in the English medical literature. Spontaneous regression of a tumefactive perivascular space along with resolution of clinical symptoms, followed by spontaneous recurrence associated with symptom recurrence is an extremely rare occurrence, which to the best of our knowledge, has not been reported in the medical literature. We describe a case of spontaneous regression of a tumefactive perivascular space, three years after its initial detection, followed by spontaneous recurrence after two years

MRI patterns of global hypoxic-ischemic injury in adults

Background and purpose: To assess MRI patterns and associated clinical outcome in adults with global hypoxic-ischemic injury. Materials and methods: In order to identify the patients with evidence of global hypoxic-ischemic injury, we retrospectively searched our radiology information system for reports of brain MRI studies from 01/01/2004 to 12/31/2010, containing the keywords - "hypoxia", "hypoxic", "anoxia" and "anoxic". A board certified neuroradiologist visually inspected the corresponding MR images for the presence, location and extent (focal versus diffuse) of ischemic findings. Clinical data for these patients was collected from the electronic medical records, including mechanism of the hypoxic-ischemic injury, and clinical outcome was measured using modified Rankin Scale (mRS). Results: Review of radiology reports identified 151 cases, of which 64 patients remained after exclusion of normal studies ("no hypoxia" in the report), pediatric patients and patients with remote perinatal hypoxia. Five patients had relatively favorable clinical outcome (mRS of 1 to 3) and 59 had poor outcome (mRS of 4 to 6). Patterns associated with relatively favorable clinical outcome were: a) watershed pattern and b) basal ganglia without cortical involvement. Patterns associated with poor clinical outcome were: a) diffuse cortical and deep grey matter pattern, with and without perirolandic sparing; (b) medial occipital with perirolandic involvement; c) precentral gyrus involvement; d) diffuse white matter involvement; e) brainstem involvement; f) cerebellar involvement and g) hippocampal involvement. Conclusion: The vast majority of patients with MRI patterns of hypoxic-anoxic injury have a poor clinical outcome, independently of the observed pattern, with the only relative exception being the watershed pattern and the basal ganglia pattern without cortical involvement. (C) 2012 Elsevier Masson SAS. All rights reserved

Susac syndrome in a young child

Susac syndrome is a microangiopathy of unknown origin affecting the brain, retina and inner ear. This rare entity is often misdiagnosed as a demyelinating condition such as multiple sclerosis or acute disseminated encephalomyelitis. A high index of suspicion must be present as the majority of patients do not have the complete clinical triad at the time of onset of symptoms. The radiologist plays an important role when the disease is suspected and helps orient the investigations. The syndrome has characteristic imaging features on MRI that include multifocal white matter and occasional grey matter lesions, the corpus callosum being always involved. The predominant central callosal lesions, especially with rapid cystic transformation (central callosal holes) can be considered pathognomonic of this condition in the appropriate clinical setting. This disease is extremely rare in children. We report a case of Susac syndrome in a 9-year-old girl to increase the awareness among paediatric radiologists of this entity, which is usually not considered as a differential diagnosis of multifocal white matter involvement in this age group

Bilateral Massive Angiomyolipomatosis Associated with Tuberous Sclerosis

Angiomyolipoma is an uncommon tumor consisting of vascular, smooth muscle, and fatty elements. Angiomyolipoma can present in two forms; as an isolated unilateral lesion which occurs sporadically or as bilateral lesions associated with tuberous sclerosis and Von Hippel-Lindau syndrome. Bilateral massive angiomyolipomatosis is a very rare entity. Only three cases have been reported in medical literature. We present a case of bilateral massive angiomyolipomatosis associated with tuberous sclerosis

Isolated contralateral sudden sensorineural hearing loss: an unusual manifestation of pontine infarct

Unilateral, acute onset sensorineural hearing loss ("sudden sensorineural hearing loss" [SSNHL]) as an isolated event without other associated neurological deficits usually results from a lesion of the cochlea. Lesions in the ascending central auditory pathways cranial to the cochlear nucleus seldom result in unilateral hearing loss due to decussation of the central auditory pathways at multiple levels. We describe a patient with a tiny acute infarct in the right pons resulting in isolated acute onset left-sided SSHNL, without any other associated acute neurological deficits