Amplification of Reynolds number dependent processes by wave distortion

A system using a hot-wire transducer as an analog of a liquid droplet of propellant was employed to investigate the ingredients of the acoustic instability of liquid-propellant rocket engines. It was assumed that the combustion process was vaporization-limited and that the combustion chamber was acoustically similar to a closed-closed right-circular cylinder. Before studying the hot-wire closed-loop system (the analog system), a microphone closed-loop system, which used the response of a microphone as the source of a linear feedback exciting signal, was investigated to establish the characteristics of self-sustenance of acoustic fields. Self-sustained acoustic fields were found to occur only at resonant frequencies of the chamber. In the hot-wire closed-loop system, the response of hot-wire anemometer was used as the source of the feedback exciting signal. The self-sustained acoustic fields which developed in the system were always found to be harmonically distorted and to have as their fundamental frquency a resonant frequency for which there also existed a second resonant frequency which was approximately twice the fundamental frequency

Optimal control of motorsport differentials

Modern motorsport limited slip differentials (LSD) have evolved to become highly adjustable, allowing the torque bias that they generate to be tuned in the corner entry, apex and corner exit phases of typical on-track manoeuvres. The task of finding the optimal torque bias profile under such varied vehicle conditions is complex. This paper presents a nonlinear optimal control method which is used to find the minimum time optimal torque bias profile through a lane change manoeuvre. The results are compared to traditional open and fully locked differential strategies, in addition to considering related vehicle stability and agility metrics. An investigation into how the optimal torque bias profile changes with reduced track-tyre friction is also included in the analysis. The optimal LSD profile was shown to give a performance gain over its locked differential counterpart in key areas of the manoeuvre where a quick direction change is required. The methodology proposed can be used to find both optimal passive LSD characteristics and as the basis of a semi-active LSD control algorithm

Analysis and study of hospital communication via social media from the patient perspective

Currently, the online interaction between citizens and hospitals is poor, as users believe that there are shortcomings that could be improved. This study analyzes patients’ opinions of the online communication strategies of hospitals in Spain. Therefore, a mixed-method is proposed. Firstly, a qualitative analysis through a focus-group was carried out, so around twenty representatives of national, regional and local patients’ associations were brought together. Secondly, the research is supplemented with a content assessment of the Twitter activity of the most influential hospitals in Spain. The results reveal that the general public appreciate hospitals’ communication potential through social media, although they are generally unaware of how it works. The group says that, apart from the lack of interaction, they find it hard to understand certain messages, and some publications give a biased picture. In order to improve communication, patients and relatives are demanding that their perspective be taken into consideration in the messages issued to enhance the quality of life and well-being of society

Cavity optomechanics with Si3N4 membranes at cryogenic temperatures

We describe a cryogenic cavity-optomechanical system that combines Si3N4 membranes with a mechanically-rigid Fabry-Perot cavity. The extremely high quality-factor frequency products of the membranes allow us to cool a MHz mechanical mode to a phonon occupation of less than 10, starting at a bath temperature of 5 kelvin. We show that even at cold temperatures thermally-occupied mechanical modes of the cavity elements can be a limitation, and we discuss methods to reduce these effects sufficiently to achieve ground state cooling. This promising new platform should have versatile uses for hybrid devices and searches for radiation pressure shot noise.Comment: 19 pages, 5 figures, submitted to New Journal of Physic

Escape from the Phagosome: The Explanation for MHC-I Processing of Mycobacterial Antigens?

Mycobacterium tuberculosis (Mtb) is thought to live in an altered phagosomal environment. In this setting, the mechanisms by which mycobacterial antigens access the major histocompatibility class I (MHC-I) processing machinery remain incompletely understood. There is evidence that Mtb antigens can be processed in both endocytic and cytosolic environments, with different mechanisms being proposed for how Mtb antigens can access the cytosol. Recently, electron microscopy was used to demonstrate that Mtb has the potential to escape the phagosome and reside in the cytosol. This was postulated as the primary mechanism by which Mtb antigens enter the MHC-I processing and presentation pathway. In this commentary, we will review data on the escape of Mtb from the cytosol and whether this escape is required for antigen presentation to CD8+ T cells

Bose-Einstein condensation in a circular waveguide

We have produced Bose-Einstein condensates in a ring-shaped magnetic waveguide. The few-millimeter diameter non-zero bias ring is formed from a time-averaged quadrupole ring. Condensates which propagate around the ring make several revolutions within the time it takes for them to expand to fill the ring. The ring shape is ideally suited for studies of vorticity in a multiply-connected geometry and is promising as a rotation sensor.Comment: 4 pages, 4 figure

An investigation of the open-loop amplification of Reynolds number dependent processes by wave distortion

Analytical and experimental studies were initiated to determine if the response of a constant temperature hot wire anemometer to acoustic oscillations could serve as an analog to the response of the drop vaporization burning rate process to acoustic oscillations, and, perhaps, also as an analog to any Reynolds number dependent process. The motivation behind this study was a recent analytical study which showed that distorted acoustic oscillations could amplify the open-loop response of vaporization limited combustion. This type of amplification may be the cause of unstable combustion in liquid propellant rocket engines. The analytical results obtained for the constant temperature anemometer are similar in nature to those previously obtained for vaporization limited combustion and indicate that the response is dependent on the amount and type of distortion as well as other factors, such as sound pressure level, Mach number and hot wire temperature. Preliminary results indicate qualitative agreement between theory and experiment

Manifestation of classical wave delays in a fully quantized model of the scattering of a single photon

We consider a fully quantized model of spontaneous emission, scattering, and absorption, and study propagation of a single photon from an emitting atom to a detector atom both with and without an intervening scatterer. We find an exact quantum analog to the classical complex analytic signal of an electromagnetic wave scattered by a medium of charged oscillators. This quantum signal exhibits classical phase delays. We define a time of detection which, in the appropriate limits, exactly matches the predictions of a classically defined delay for light propagating through a medium of charged oscillators. The fully quantized model provides a simple, unambiguous, and causal interpretation of delays that seemingly imply speeds greater than c in the region of anomalous dispersion.Comment: 18 pages, 4 figures, revised for clarity, typos corrrecte