A Parabolised Stability Equation based Broadband Shock-Associated Noise Model

International audienceWavepacket models have been used extensively to predict the noise produced from turbulent subsonic and supersonic jets. Such wavepackets, which represent the organised structures of the flow, are solutions to the linearised Navier-Stokes equations. Using a kinematic two-point model, Wong et al. [1] have indicated the importance of incorporating coherence decay in modelling broadband shock-associated noise (BBSAN) in supersonic jets. In this work, we aim to improve the model by using solutions from linear parabolised stability equations (PSE) to model the wavepacket part of the BBSAN source. The two-point coherence of the wavepackets is obtained from large-eddy simulation (LES) data of a M j = 1.5 fully-expanded isothermal supersonic jet [2]. The aim is to build a dynamic sound-source model for BBSAN that would improve on the simplified line-source model proposed by Wong et al. [3]. We find that a frequency dependent coherence decay length scale is important in order to suppress the higher-order harmonic peaks [4] and to obtain the correct BBSAN peak shape. Moderate agreement up to St = 1 was found between the current noise predictions and those from experimental data. I. Nomenclature ω = wavepacket frequency θ = azimuthal coordinate c s n = amplitude coefficient of the shock cells G = Green's function k s = shock-cell wavenumber k h = hydrodynamic wavenumber L = longitudinal extent of wavepacket L c = coherence length of wavepacket m = azimuthal mode number M j = ideally-expanded Mach number r = radial coordinate u s = shock cell velocity fluctuation u t = wavepacket fluctuationŝ u * ω = velocity fluctuations at a frequency ω x = axial coordinat

Mammalian microRNA: an important modulator of host-pathogen interactions in human viral infections

MicroRNAs (miRNAs), which are small non-coding RNAs expressed by almost all metazoans, have key roles in the regulation of cell differentiation, organism development and gene expression. Thousands of miRNAs regulating approximately 60æ% of the total human genome have been identified. They regulate genetic expression either by direct cleavage or by translational repression of the target mRNAs recognized through partial complementary base pairing. The active and functional unit of miRNA is its complex with Argonaute proteins known as the microRNA-induced silencing complex (miRISC). De-regulated miRNA expression in the human cell may contribute to a diverse group of disorders including cancer, cardiovascular dysfunctions, liver damage, immunological dysfunction, metabolic syndromes and pathogenic infections. Current day studies have revealed that miRNAs are indeed a pivotal component of host-pathogen interactions and host immune responses toward microorganisms. miRNA is emerging as a tool for genetic study, therapeutic development and diagnosis for human pathogenic infections caused by viruses, bacteria, parasites and fungi. Many pathogens can exploit the host miRNA system for their own benefit such as surviving inside the host cell, replication, pathogenesis and bypassing some host immune barriers, while some express pathogen-encoded miRNA inside the host contributing to their replication, survival and/or latency. In this review, we discuss the role and significance of miRNA in relation to some pathogenic viruses

OCDMA platform for avionics applications

A scalable OCDMA platform for testing different avionics applications at Lockheed Martin has been designed and built. The platform enables communication at OC-24 per user with raw BER<10-12 using fast wavelength-hopping, time-spreading prime codes with picosecond optical pulses. A novel optical encoder/decoder pair enables a connectivity approaching a so-called 'one-time pad' security and eavesdropping studies

Improving transmission privacy using optical layer XOR

We built novel "dual code" OCDMA transmitter and receiver with optical layer XOR, thus achieving data privacy approaching One-time Pad security. Enhanced secure communication among users was demonstrated at OC-24 with raw BER < 10-12

Design and demonstration of a novel incoherent optical CDMA system

A detailed analysis of the scalability of two-dimensional optical codes is presented and two network deployment architectures for optical code division multiple access (OCDMA) are discussed. We present the architecture and or a highly scalable, 2.5 Gb/s per user code design for OCDMA system. The system is scalable to 100 potential and more than 10 simultaneous users, each with BER of less than 10(-9). The system architecture uses fast wavelength-hopping, time-spreading codes. Unlike phase sensitive coherent OCDAM systems, this architecture utilizes standard on-off-keyed optical pulses allocated in the time and wavelength domains. This incoherent OCDMA approach is compatible with existing WDM optical networks and utilizes off-the-shelf components. We discuss a novel optical subsystems design for encoders and decoders that enable the realization of a highly scalable incoherent OCDMA system with rapid reconfigurability. We demonstrate the operation of 4 simultaneous users operating at OC-48 (similar to 2.5 Gbit/s) with a power penalty of < 0.5dB and the reduction of mulliple-access interference using ultra-fast all-optical sampling with newly proposed TOAD-based OCDMA receiver

Unconventional time-bandwidth performance of resonant cavities with nonreciprocal coupling

The time-bandwidth limit is a mathematical tenet that affects all reciprocal resonators, stating that the product of the spectral bandwidth that can couple into a resonant system and its characteristic energy decay time is always equal to 1. Here, we develop an analytical and numerical model to show that introducing nonreciprocal coupling to a generalized resonator changes the power balance between the reflected and intracavity fields, which consequently overcomes the time-bandwidth limit of the resonant system. By performing a full evaluation of the time-bandwidth product (TBP) of the modeled resonator, we show that it represents a measure of the increased delay imparted to a light wave, with respect to what the bandwidth of the reciprocal resonant structure would allow to the same amount of in-coupled power. No longer restricted to the value 1, we show that the TBP can instead be used as a figure of merit of the improvement in intracavity power enhancement due to the nonreciprocal coupling. © 2021 American Physical Society

New approach to high speed optical code division multiple access networks with multidimensional codes and use of novel all-optical technology

We present the architecture and code design for a highly scalable, 2.5 Gbis per user optical code division multiple access (OCDMA) system. The system is scalable to 100 potential and more than 10 simultaneous users, each with BER of less than 10-9. The system architecture uses a fast frequency-hopping, time-spreading codes. Unlike frequency and phase sensitive coherent OCDMA systems, this architecture utilizes standard on-off keyed optical pulses allocated in the time and wavelength dimensions. This incoherent OCDMA approach is compatible with existing WDM optical networks and utilizes off the shelf components. We discuss the novel optical subsystem designs for encoders and decoders that enable the realization of a highly scalable incoherent OCDMA system with rapid reconfigurability. A detailed analysis of the scalability of the two dimensional code is presented. Broadcast and select network deployment architectures for OCDMA are discussed

Optical approach to avionic platforms based on OCDMA

We built scalable OCDMA platform under DARPA contract and delivered to Lockheed-Martin for additional testing. Demonstrated platform enables secure communications among users using an optical XOR gate at OC-24 with 10 -12 or better raw BER