The Mach–Zehnder interferometer with the finite fringe method is applied for the first time to diagnose the three-dimensional density field of a shock-containing microjet issued from a convergent ...nozzle with an inner diameter of 1 mm at the exit. Experiments are performed at a nozzle pressure ratio of 4.0 to produce an underexpanded free jet with a Mach disk in the first shock-cell where the Reynolds number, based upon the diameter and flow properties at the nozzle exit, is
$5.91\times 10^{4}$
. Interferogram analyses for reconstructing the jet density fields are performed using the Abel inversion method, in which the analysis of the phase shift of the deformed fringe relative to the background fringe is carried out by the Fourier transform method. In addition to experiments, the flow field of the shock-containing microjet is simulated by solving the Reynolds-averaged Navier–Stokes equations with the SST
$k$
–
$\unicodeSTIX{x1D714}$
turbulence model for a quantitative mutual comparison between the simulation and the experiment. The detailed variation of the density field associated with the Mach disk, the slip streams and the outer shear layers near the jet boundaries are successfully captured. Furthermore, the density profile along the jet centreline obtained by the present experiment is quantitatively compared with those from prior quantitative visualization studies, such as rainbow schlieren deflectometry, background oriented schlieren, moiré schlieren and Mach–Zehnder interferometer. The three-dimensional contour map coloured by the magnitude of the density gradient vector inside the microjet reveals the flow topology of the near-field shock systems and elucidates the spatial variation of the shock strength.
In recent years, distributed generation, as clean natural energy generation and cogeneration system of high thermal efficiency, has increased due to the problems of global warming and exhaustion of ...fossil fuels. Many of the distributed generations are set up in the vicinity of the customer, with the advantage that this decreases transmission losses. However, output power generated from natural energy, such as wind power, photovoltaics, etc., which is distributed generation, is influenced by meteorological conditions. Therefore, when the distributed generation increases by conventional control techniques, it is expected that the voltage change of each node becomes a problem. Proposed in this paper is the optimal control of distribution voltage with coordination of distributed installations, such as the load ratio control transformer, step voltage regulator (SVR), shunt capacitor, shunt reactor, and static var compensator. In this research, SVR is assumed to be a model with tap changing where the signal is received from a central control unit. Moreover, the communication infrastructure in the supply of a distribution system is assumed to be widespread. The genetic algorithm is used to determine the operation of this control. In order to confirm the validity of the proposed method, simulations are carried out for a distribution network model with distributed generation (photovoltaic generation).
The aim of this study was to investigate the epidemiology of post-COVID conditions beyond 12 months and identify factors associated with the persistence of each condition.
This was a cross-sectional ...questionnaire-based survey.
We conducted the survey among patients who had recovered from COVID-19 and visited our institute between February 2020 and November 2021. Demographic and clinical data and data regarding the presence and duration of post-COVID conditions were obtained. We identified factors associated with the persistence of post-COVID conditions using multivariable linear regression analyses.
Of 1148 surveyed patients, 502 completed the survey (response rate, 43.7%). Of these, 393 patients (86.4%) had mild disease in the acute phase. The proportion of participants with at least one symptom at 6, 12, 18, and 24 months after symptom onset or COVID-19 diagnosis was 32.3% (124/384), 30.5% (71/233), 25.8% (24/93), and 33.3% (2/6), respectively. The observed associations were as follows: fatigue persistence with moderate or severe COVID-19 (β = 0.53, 95% confidence interval CI = 0.06–0.99); shortness of breath with moderate or severe COVID-19 (β = 1.39, 95% CI = 0.91–1.87); cough with moderate or severe COVID-19 (β = 0.84, 95% CI = 0.40–1.29); dysosmia with being female (β = −0.57, 95% CI = −0.97 to −0.18) and absence of underlying medical conditions (β = −0.43, 95% CI = −0.82 to −0.05); hair loss with being female (β = −0.61, 95% CI = −1.00 to −0.22), absence of underlying medical conditions (β = −0.42, 95% CI = −0.80 to 0.04), and moderate or severe COVID-19 (β = 0.97, 95% CI = 0.41–1.54); depressed mood with younger age (β = −0.02, 95% CI = −0.04 to −0.004); and loss of concentration with being female (β = −0.51, 95% CI = −0.94 to −0.09).
More than one-fourth of patients after recovery from COVID-19, most of whom had had mild disease in the acute phase, had at least one symptom at 6, 12, 18, and 24 months after onset of COVID-19, indicating that not a few patients with COVID-19 suffer from long-term residual symptoms, even in mild cases.
A new measurement technique to reconstruct the density field of the shock-wave/boundary-layer interaction (SWBLI) in a confined duct is proposed. With this technique, it is possible to quantitatively ...capture in detail the structures of the density field both in the regions of the shock-systems in the central core and boundary-layer flows near the duct wall concurrently. The novel feature of the proposed technique is to make use of the schlieren images with the rainbow filters of the vertical and horizontal cutoff settings and then to reconstruct the two-dimensional density field integrated over the line-of-sight direction using the corresponding filter calibration curves. The proposed technique is applied for the first time to a shock train in a constant-area straight duct under the upstream condition of the shock train: the freestream Mach number is 1.42, the incoming boundary layer thickness normalised by the duct half height is 0.175, and the corresponding unit Reynolds number
$Re/m$
is
$2.99 \times 10^7$
m-1. The calculated isopycnic field depicts the streamwise and transverse density variations inside the shock train, the mixing region after the shock train, and the boundary-layer of the interaction region. This technique is shown to be capable of identifying the locations of shocks in a shock train more precisely than a conventional approach measuring the static pressure distribution along the duct wall. In addition, various quantitative visual representations such as a shadowgraphy and a bright-field schlieren can be extracted from the density field acquired by the present approach, and the spatial evolution of the shape and strength of each shock constituting the shock train as well as the boundary layer flow properties can be quantitatively clarified.
We analysed associations between exposure to nightlife businesses and severe acute respiratory syndrome coronavirus 2 PCR test results at a tertiary hospital in Tokyo between March and April 2020. A ...nightlife group was defined as those who had worked at or visited the businesses. We included 1517 individuals; 196 (12.9%) were categorised as the nightlife group. After propensity score matching, the proportion of positive PCR tests in the nightlife group was significantly higher than that in the non-nightlife group (nightlife, 63.8%; non-nightlife, 23.0%; P < 0.001). An inclusive approach to mitigate risks related to the businesses needs to be identified.
The COVID-19 pandemic has had variable effects on the rates of STIs reported across the globe. This study sought to assess how the number of STI reports changed during the pandemic in Japan.
We used ...national infectious disease surveillance data from the National Institute of Infectious Diseases (Tokyo, Japan) for the period between January 2013 and December 2021. We compared reported rates of chlamydia, gonorrhoea, condyloma acuminata and genital herpes, as well as total notifications for HIV/AIDS and syphilis during the pandemic versus previous years in Japan. We used a quasi-Poisson regression to determine whether any given week or month between January 2018 and December 2021 had a significant excess or deficit of STIs. Notification values above or below the 95% upper and lower prediction thresholds were considered as statistically significant. The start of the pandemic was defined as January 2020.
Chlamydia generally remained within predicted range during the pandemic period. Reporting of gonorrhoea was significantly higher than expected throughout early-to-mid 2021 but otherwise generally remained within predicted range prior to 2021. Condyloma, herpes and HIV/AIDS reporting were transiently significantly lower than expected throughout the pandemic period, but no significant periods of higher-than-expected reporting were detected. Syphilis showed widespread evidence of significantly lower-than-predicted reporting throughout 2020 but eventually reversed, showing significantly higher-than-predicted reporting in mid-to-late 2021.
The COVID-19 pandemic was associated with variable changes in the reporting of STIs in Japan. Higher-than-predicted reporting was more likely to be observed in the later phases of the pandemic. These changes may have been attributable to pandemic-related changes in sexual behaviour and decreased STI clinic attendance and testing, but further research on the long-term impact of the pandemic on STIs is necessary.
The present study describes a new technique for the reduction of supersonic jet noise using a control wire device that is placed into the supersonic jet stream. The control wire device is composed of ...long cylinders with a very small diameter and its location is varied to investigate the control effectiveness of supersonic jet noise. The jet pressure ratio is varied to obtain the supersonic jets which are operated in a wide range of over-expanded to moderately under-expanded conditions. A high-quality Schlieren optical system is used to visualize the flow field of supersonic jets both with and without the control wire device. In order to quantify the control effect of the wire device on a supersonic jet, pressure measurements are also accomplished. Acoustic measurements are performed to obtain the overall sound pressure level and noise spectra. The results obtained show that the present wire device effectively breaks the shock-cell structure, reduces the shock strength, and consequently leads to a substantial suppression of supersonic jet noise. The location of the control wire device is an important factor in reducing the supersonic jet noise. The present wire device suppresses the screech tones and the broadband shock-associated noise as well as the overall sound pressure level, when it is placed at a location smaller than three times the exit diameter of nozzle in the downstream of the nozzle exit. For over-expanded jets, the noise control effectiveness of the wire device appears more significant, compared to under-expanded jets.
The interaction between a normal shock wave and a boundary layer along a wall surface in internal compressible flows causes a very complicated flow. When the shock is strong enough to separate the ...boundary layer, the shock is bifurcated and one or more shocks appear downstream of the bifurcated shock. A series of shocks thus formed, called “shock train”, is followed by an adverse pressure gradient region, if the duct is long enough. Thus the effect of the interaction extends over a great distance. The flow is decelerated from supersonic to subsonic through the whole interaction region. In this sense, the interaction region including the shock train in it is referred to as “pseudo-shock” in the present paper, as Crocco called it. The shock train and pseudo-shock strongly affect the performance and efficiency of various flow devices. In the present review some fundamental characteristics of the shock train and pseudo-shock are first described. Some simple predictions are made to simulate these very complicated phenomena. Pseudo-shocks appearing in various flow devices are explained. Control methods of the pseudo-shocks are also described. Finally, the current understanding of self-excited oscillation of pseudo-shock is reviewed.
The behavior of an incident shock wave into a Helmholtz resonator is very important from the acoustical point of view as well as the fundamental researches of shock wave dynamics. When a shock wave ...propagates into a Helmholtz resonator, complicated wave phenomena are formed both inside and outside the resonator. Shock wave reflections, shock wave focusing phenomena, and shock–vortex interactions cause strong pressure fluctuations inside the resonator, consequently leading to powerful sound emission. The wave phenomena inside the resonator are influenced by detailed configuration of the resonator. It is well known that the gas inside the resonator strongly oscillates at a resonance frequency, as the incident wavelength is larger, compared with the geometrical length scale of the resonator, but there are only a few works regarding a shock wave that has an extremely short wavelength. Meanwhile, the discharge process of the incident shock wave from the resonator is another interest with regard to an impulse wave generation that is a source of serious noise and vibration problems of the resonator. In the present study, the wave phenomena inside and outside the Helmholtz resonator are, in detail, investigated with a help of a computational fluid dynamics method. The incident shock Mach number is varied below 2.0, and many different types of the resonators are explored to investigate the influence of the resonator geometry on the wave phenomena. A total variation diminishing (TVD) scheme is employed to solve two-dimensional, unsteady, compressible Euler equations. The computational results are compared with existing experimental data to ensure that the present computations are valid to predict the resonator wave phenomena. Based upon the results obtained, the shock wave focusing and discharge processes, which are important in determining the resonator flow characteristics, are discussed in detail.
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