Non-normality and transient growth in stall flutter instability.

The non-normal nature and transient growth in amplitude and energy of a pitch-plunge aeroelastic system undergoing dynamic stall are explored in this paper through numerical and supporting experimental studies. Wind tunnel experiments, carried out for a canonical pitch-plunge aeroelastic system in a subsonic wind tunnel, show that the system undergoes stall flutter instability via a sub-critical Hopf bifurcation. The aeroelastic responses indicate a transient growth in amplitude and energy-possibly triggering the sub-criticality, which is critical from the purview of structural safety.

A review of plant-based natural dyes in leather application with a special focus on color fastness characteristics.

Dyes/colorants are normally used to improve the aesthetic of consumer products, and leather is one of them. The leather industry plays a significant role in the global economy. However, the leather-making process causes severe environmental pollution.

Experimental investigation on the synchronization characteristics of a pitch-plunge aeroelastic system exhibiting stall flutter.

This study focuses on characterizing the bifurcation scenario and the underlying synchrony behavior in a nonlinear aeroelastic system under deterministic as well as stochastic inflow conditions. Wind tunnel experiments are carried out for a canonical pitch-plunge aeroelastic system subjected to dynamic stall conditions. The system is observed to undergo a subcritical Hopf bifurcation, giving way to large-amplitude limit cycle oscillations (LCOs) in the stall flutter regime under the deterministic flow conditions.

Effect of parameter mismatch and dissipative coupling on amplitude death regime in a coupled nonlinear aeroelastic system.

Amplitude death (AD) has been recently identified as a phenomenon that can be exploited to stop unwanted large amplitude oscillations arising from instabilities in engineering systems. These oscillations are a consequence of the occurrence of dynamic instability, for example, the flutter instability, which results in the manifestation of sustained limit cycle oscillations. Recent studies have demonstrated amplitude death in coupled aeroelastic systems with identical parameters using suitable reactive coupling.

Synchronization of pitch and plunge motions during intermittency route to aeroelastic flutter.

Interaction of fluid forces with flexible structures is often prone to dynamical instabilities, such as aeroelastic flutter. The onset of this instability is marked by sustained large amplitude oscillations and is detrimental to the structure's integrity. Therefore, investigating the possible physical mechanisms behind the onset of flutter instability has attracted considerable attention within the aeroelastic community.

Oral mucocutaneous lesions - a comparative clinicopathological and immunofluorescence study.

Background: Oral mucosa is often affected by many diseases including mucocutaneous disorders. The diagnoses of these disorders are primarily based on history, clinical features, and histopathology. For the past few years' immunofluorescence techniques emerged as an important tool to study the pathogenesis and in the diagnosis of oral mucocutaneous and vesiculobullous disorders.

Comparisons of the handheld autorefractor, table-mounted autorefractor, and subjective refraction in Singapore adults.

Purpose: The purpose of this article was to compare the Retinomax with the table-mounted autorefractor and subjective refraction in Singapore adults.

Methods: Adults (n = 100) attending a tertiary eye hospital clinic were examined by an optometrist. First, subjective refraction testing was performed using a trial lens set, followed by handheld autorefractor tests using the Nikon Retinomax and the table-mounted autorefractor (Topcon RM8000B).

Sleep deprivation in junior doctors--house officers in Singapore.

House officers are known to endure marked levels of sleep deprivation in administration of their duties. We aim to establish sleep patterns of local house officers while on the job and the impact it might have on their mood and sleepiness state. We also studied their sleep during their final year of medical school and pre-university for identification of any prior sleep deprivation.