Multi-longitudinal mode 532 nm photonic Doppler velocimetry for shock experiments.

A novel multi-longitudinal mode 532 nm photonic Doppler velocimetry (PDV) was proposed to solve the problem of high bandwidth requirements in shock experiments with velocities up to km/s. Compared to the conventional PDV system operating at 1550 nm, the utilization of a shorter wavelength of 532 nm enables nearly three times the velocity resolution. However, it also leads to a threefold increase in the Doppler frequency shift for a given velocity. To mitigate the bandwidth constraints, a multi-longitudinal mode laser is employed to downconvert the signal, effectively reducing the bandwidth requirements. The efficacy of this method is validated through theoretical analysis and experimental investigations on detonation shock scenarios. Furthermore, this approach eliminates the necessity for modulators, frequency shifters, and other devices, facilitating its applicability to non-communication bands.

A hybrid system for simultaneous velocity and distance measurements in dynamic experiments.

The accurate measurement of an object's motion requires knowledge of both its position and its velocity. The commonly used photonic Doppler velocimetry and broadband laser ranging techniques are ideal for conducting simultaneous dynamic experiments. Instead of employing two distinct measurement systems, we developed a hybrid system that can simultaneously measure velocity and distance in dynamic experiments. This reduces cost and complexity, particularly for multi-channel tests, by using only one probe, photodetector, and oscilloscope channel. By precisely synchronizing the velocity and distance data in time, the system can assist with interpreting the target's position and orientation.

Simple, non-mechanical and automatic calibration approach for axial-scanning microscopy with an electrically tunable lens.

We describe a simple and robust calibration approach for axial-scanning microscopy that realizes axial focus shifts with an electrically tunable lens (ETL). We demonstrate the calibration approach based on a microscope with an ETL placed close to the rear stop of the objective lens. By introducing a target-consisted of repeating lines at one known frequency and placed at a ~45° angle to the imaging path, the calibration method captures multiple images at different ETL currents and calibrates the dependence of the axial focus shift on the ETL current by evaluating the sharpness of the captured images. It calibrates the dependence of the magnification of the microscope on the ETL current by measuring the period of the repeating lines in the captured images. The experimental results show that different from the conventional calibration procedure, the proposed scheme does not involve any mechanical scanning and can simultaneously calibrate the dependence of the axial focus shift and the magnification on the ETL current. This might facilitate imaging studies that require the measurement of fine structures in a 3D volume. We also show the calibration procedure can be used to estimate the radius of a conner-arc sample, fabricated using laser micromachining. We believe that this easy-to-use calibration approach may facilitate use of ETLs for a variety of imaging platforms. It may also provide new insights for the development of novel 3D surface measurement methods. RESEARCH HIGHLIGHTS: The proposed calibration scheme does not involve any mechanical scanning and can simultaneously calibrate the dependence of the axial focus shift and the magnification on the electrically tunable lens (ETL) current. It might facilitate imaging studies that require the measurement of fine structures in a 3D volume, and the use of ETLs for a variety of imaging platforms. It may also provide new insights for the development of novel 3D surface measurement methods.

Clinical characteristics and drug therapies in patients with the common-type coronavirus disease 2019 in Hunan, China.

Background Clinical characteristics of patients with the coronavirus disease 2019 (COVID-19) may present differently within and outside the epicenter of Wuhan, China. More clinical investigations are needed. Objective The study was aimed to describe the clinical characteristics, laboratory parameters, and therapeutic methods of COVID-19 patients in Hunan, China. Setting The First Hospital of Changsha, First People's Hospital of Huaihua, and the Central Hospital of Loudi, Hunan province, China. Methods This was a retrospective multi-center case-series analysis. Patients with confirmed COVID-19 diagnosis hospitalized at the study centers from January 17 to February 10, 2020, were included. The following data were obtained from electronic medical records: demographics, medical history, exposure history, underlying comorbidities, symptoms, signs, laboratory findings, computer tomography scans, and treatment measures. Main outcome measure Epidemiological, clinical, laboratory, and radiological characteristics and treatments. Results A total of 54 patients were included (51 had the common-type COVID-19, three had the severe-type), the median age was 41, and 52% of them were men. The median time from the first symptoms to hospital admission was seven days. Among patients with the common-type COVID-19, the median length of stay was nine days, and 21 days among patients with severe COVID-19. The most common symptoms at the onset of illness were fever (74.5%), cough (56.9%), and fatigue (43.1%) among patients in the common-type group. Fourteen patients (37.8%) had a reduced WBC count, 23 (62.2%) had reduced eosinophil ratio, and 21 (56.76%) had decreased eosinophil count. The most common patterns on chest-computed tomography were ground-glass opacity (52.2%) and patchy bilateral shadowing (73.9%). Pharmacotherapy included recombinant human interferon α2b, lopinavir/ritonavir, novaferon, antibiotics, systematic corticosteroids and traditional Chinese medicine prescription. The outcome of treatment indicated that in patients with the common-type COVID-19, interferon-α2b, but not novaferon, had some benefits, antibiotics treatment was not needed, and corticosteroids should be used cautiously. Conclusion As of February 10, 2020, the symptoms of COVID-19 patients in Hunan province were relatively mild comparing to patients in Wuhan, the epicenter. We observed some treatment benefits with interferon-α2b and corticosteroid therapies but not with novaferon and antibiotic treatment in our study population.

Multi-reference broadband laser ranging to increase the measuring range.

Broadband laser ranging (BLR) is an appropriate method to obtain absolute distance in dynamic experiments. In this article, we first analyze the performance limit for BLR and indicate that the measuring range can be hardly increased while keeping the distance or time resolution unchanged. Then, multi-reference BLR is proposed, which can break this limit and greatly increase the measuring range. Its validity is demonstrated by an experiment with an explosively driven aluminum surface flying over 100 mm. This method would improve the capability of BLR.

A novel photonic Doppler velocimetry for transverse velocity measurement.

A fiber interferometry for transverse velocity measurement has been developed. This diagnostic is similar to photonic Doppler velocimetry in the way in which laser propagates and couples. The interferometer mainly consists of a fiber coupler, an emitting probe, and two receiving probes. A pair of scattered laser beams mix in the coupler and generates fringes with frequency proportional to transverse velocity. Measurement of transverse velocity is independent of longitudinal velocity. The feasibility of the technique has been verified by rotating wheel experiment and shock loading experiment.

Analysis of photonic Doppler velocimetry data based on the continuous wavelet transform.

The short time Fourier transform (STFT) cannot resolve rapid velocity changes in most photonic Doppler velocimetry (PDV) data. A practical analysis method based on the continuous wavelet transform (CWT) was presented to overcome this difficulty. The adaptability of the wavelet family predicates that the continuous wavelet transform uses an adaptive time window to estimate the instantaneous frequency of signals. The local frequencies of signal are accurately determined by finding the ridge in the spectrogram of the CWT and then are converted to target velocity according to the Doppler effects. A performance comparison between the CWT and STFT is demonstrated by a plate-impact experiment data. The results illustrate that the new method is automatic and adequate for analysis of PDV data.