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Review of Infrared signature suppression systems using optical blocking method
摘要： With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line-Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.
关键词： IR signature level,Performance penalty,Engine back-pressure,IR signature suppression,Optical blocking
更新于2025-09-23 15:23:52
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Pressure dependence of high order harmonic generation in nitrogen molecular gas and atmospheric air
摘要： The effect of the variation of the gas pressure on the high harmonic generation (HHG) from nitrogen molecular gas (N2) and atmospheric air with ultrashort intense laser pulses is measured. The optimum pressure in the interaction region of a gas jet for maximizing the HHG yield is determined for both gases. Enhancement of the HHG output and its extension to higher harmonic orders are observed around the optimum pressure value of 0.33 bar. Theoretical calculations based on one-dimensional models explain this effect and provide reasonable agreement with experimental results.
关键词： Femtosecond laser,Conversion efficiency,High-order harmonic generation (HHG),Phase matching,XUV radiation,Pressure optimization
更新于2025-09-23 15:23:52
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Pressure effect on phosphor thermometry using Mg <sub/>4</sub> FGeO <sub/>6</sub> :Mn
摘要： This study examined the effect of ambient pressure on the luminescent lifetime of Mg4FGeO6:Mn phosphors in different morphologies. To evaluate the pressure sensitivity of phosphor in the form of particle, agglomerated particle and chemically bonded coating, samples including phosphor powder, pressed phosphor disc, and chemically bonded phosphor coating were fabricated and calibrated using a PMT-based measurement system for a pressure range of 20-200 kPa and a temperature range of 298-873 K. The results showed no obvious pressure effect on the lifetime of the chemically bonded Mg4FGeO6:Mn coating. However, the lifetime of the phosphor powder and pressed phosphor disc decreased as pressure increased. This pressure effect was most obvious for the pressed phosphor disc, which was further aggravated at higher temperatures. The atomic distance between manganese ion and other atomics reduced as pressure increased, which induced the movement of excited state in the configuration coordinate. Considering this dependency of pressure sensitivity on phosphor morphology, it is important to adopt the same fabrication procedure for calibration and temperature measurement using Mg4FGeO6:Mn. In addition, for in-flow measurement using Mg4FGeO6:Mn tracer particles, the influence of environmental pressure must be considered.
关键词： Phosphor thermometry,Lifetime,Mg4FGeO6:Mn,Pressure effect
更新于2025-09-23 15:23:52
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Shock synthesis of Sr2Si5N8:Eu2+ phosphor
摘要： A new approach to synthesise the red-emitting nitridosilicate phosphor Sr2Si5N8:Eu2+ using shock waves is described. The solid state reaction of a mixture of Si3N4, Sr3N2 and EuN was induced using a detonation-driven shock wave apparatus. The obtained products consist of Sr2Si5N8:Eu2+ with a purity of 80–89 %, containing 7–9 % of SrSi7N10 and 4–11 % α-Si3N4, according to Rietveld analyses. Crystallites with sizes of 240–310 nm are formed, yielding particles of 2–3 μm grain size. The luminescence properties are similar to conventionally produced Sr2Si5N8:Eu2+ phosphors.
关键词： High-pressure,Phosphors,Luminescence,Solid state reaction
更新于2025-09-23 15:23:52
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Weak-value amplification of photon-number operators in the optomechanical interaction
摘要： An experimental proposal is presented in which dark port postselection together with weak measurements are used to enlarge the radiation pressure effect of a single photon on a mechanical oscillator placed in the middle of a Fabry-Pérot cavity and initialized in the ground state. By preparing and postselecting the photon (the system) in two quasiorthogonal states, the weak value of the radiation force operator can lie outside the eigenvalue spectrum, producing a large shift on the wave function of the mechanical oscillator (the measuring device) in the position representation. Consequently, the effect of a single photon on the average position of the oscillator can be amplified as compared to the effect caused by a photon without postselection, i.e., only preselected. The strong measurement scenario is also analyzed. In this case, a higher amplification effect is achieved and the mean position of the oscillator can reach the level of the zero-point fluctuations, but the postselection probabilities are smaller. Finally, the situation in which the oscillator starts in a thermal equilibrium state is studied. In this case, the amplification of the average position remains the same, i.e., proportional to the weak value, but the signal-to-noise ratio is reduced by a factor that depends on the average number of thermal phonons.
关键词： weak measurements,weak-value amplification,optomechanics,postselection,radiation pressure
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Biomedical Circuits and Systems Conference (BioCAS) - Cleveland, OH, USA (2018.10.17-2018.10.19)] 2018 IEEE Biomedical Circuits and Systems Conference (BioCAS) - Continuous Peripheral Blood Pressure Measurement with ECG and PPG Signals at Fingertips
摘要： A good habit of measuring blood pressure (BP) daily is helpful for us to stay healthy or to monitor hypertensive conditions. However, the conventional method of measuring BP using a pressure cuff has many weaknesses. In order to eliminate the use of this pressure cuff, we proposed a system using the pulse arrival time (PAT) to measure BP. This PAT can be measured using time difference between the R-peaks of electrocardiogram (ECG) and photoplethysmography (PPG) signals. In our system, we obtained these two signals by using our self-designed ECG and PPG sensors. Our sensors were fabricated in 0.18 μm CMOS technology with a small recording area of about 2.53 mm2 and 6.25 mm2, respectively. Our ECG sensor has variable amplifying gains and can achieve a total maximum gain of 60 dB. Besides that, it has a high pass filter with wide cutoff frequencies between 0.1-200 Hz, and low pass filter with cutoff frequencies of 0.2-10 kHz. The design of our ECG circuit allows us to obtain the ECG signals using fingertips and without using a ground electrode. This compact system has the potential to become a wireless wearable in the future. The measured PAT was fitted into a mathematical model and cuff-less BP readings were obtained. A plot of reference BP using oscillometric cuff and cuff-less BP showed a good correlation of r = 0.83 for systolic blood pressure (SBP). The SBP and diastolic blood pressure (DBP) mean absolute difference for the system are 6.75 mmHg and 6.08 mmHg respectively, which fairly passed the strict standard set by IEEE. In the future, our system will be compared with the use of sphygmomanometer, which is the gold standard, to further evaluate its accuracies.
关键词： blood pressure,pulse arrival time,electrocardiogram,cuff-less,photoplethysmogram
更新于2025-09-23 15:23:52
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Inactivation efficiency of Bacillus endospores via modified flow-through PUV treatment with comparison to conventional LPUV treatment
摘要： Water is a fragile resource, consequently there is a pressing need to develop sustainable environmental-friendly disinfection technologies. This constitutes the first study to compare efficacy of continuous low-pressure UV (LPUV) to that of pulsed UV light (PUV) for UV disinfection performance in flow-through water systems. Bacillus endospores were used as these are frequently deployed as biodosimeters for drinking water UV reactor validation protocols. Results showed a PUV system output of 2,052 mJ/cm2 (energy below 300 nm) was required for a 2 log inactivation of B.pumilus endospores, whereas a lower LPUV system output of 12 mJ/cm2 produced a similar level of disinfection. Measurements of dose incident to the samples (which were 10.75 cm from the PUV light source) showed supplementation of cultivation media with manganese sulphate monohydrate (MnSO4.H2O) employed to enhance the rate of endospore formation for propagation was shown to increase the UV resistance of different Bacillus spp. to both irradiation approaches (P < 0.05). Conventional LPUV light that is commonly-used by the drinking water industry is a reliable and superior approach to PUV which requires substantial modification for effective disinfection of continuous flow-through water. Caution must also be exercised when manipulating media formulation to propagate endospores as this may lead to inconsistencies in reporting efficacy of intervention treatments with implications for validation and environmental evaluation.
关键词： Bacillus endospores,Pulsed UV,Low-pressure UV,Disinfection,Media formulation
更新于2025-09-23 15:23:52
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Unusual pressure-induced electronic structure evolution in organometal halide perovskite predicted from first-principles
摘要： Pressure has been demonstrated to be an effective parameter to alter the atomic and electronic structures of materials. By using the first-principles calculations based on density functional theory (DFT), we systematically investigated the changes in the atomic and electronic structures of the cubic MAPbI3 phase under pressures. It is found that the band gap of the compressed cubic MAPbI3 structure exhibits a remarkable redshift to 1.114/1.380 eV in DFT/HSE-SOC calculation under a mild pressure of 2.772 GPa, and subsequently shows a widening at higher pressures until ~20 GPa. As the pressure further increases, the band gap closes at ~80 GPa. Detailed structural and electronic characteristic analyses indicate that the band gap of the cubic MAPbI3 structure is determined by two competing effects: the lattice contraction decreases its band gap while the PbI6 octahedral tilting increases it. Given that, pressure can be a powerful tool to help understanding the optoelectronic properties of perovskite materials.
关键词： Density functional theory,Pressure,Organometal halide perovskite,Electronic structure
更新于2025-09-23 15:23:52
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Spectral analysis for photoacoustic pressure sensor designs: Theoretical model improvement and experimental validation
摘要： In the pulsed laser photoacoustic (PA) detection and spectroscopy applications, the fundamental frequency of the PA signal produced, and the sensor resonance frequency should be as close as possible to each other so that analyzes from the obtained signals can be performed effectively. In order to determine the fundamental frequency of the PA wave, a theoretical model approach based on the development of the frequency domain solution of the PA wave equation is presented for use in the PA pressure sensor designs. For the validation of the theoretical model approach, a PA experimental setup was established, and measurements were made in distilled water. The theoretical and experimental PA frequency spectra were determined to be very compatible with each other. Thus, the theoretical model approach was experimentally validated. According to the theoretical model approach, fundamental frequency values obtained from the experimental measurement results were determined with an average accuracy of ? 4.212%. Furthermore, it has been determined that this value has fallen to ?0.267% in the measurements. With the obtained results from the theoretical model approach, we propose that PA pressure sensors with the more selective and narrower band can be designed for more sensitive detection. Moreover, in this study the effects of different laser parameters such that pulse duration, and laser beam width, on the spectral content of the obtained PA signal are analyzed. These analyses will shed light on the vision of acoustic pressure sensor design by helping to select the most optimum parameters for PA detection.
关键词： Theoretical model approach,Photoacoustic wave equation,Acoustic pressure sensor,Frequency domain solution,Pulsed laser photoacoustic method,Spectroscopy
更新于2025-09-23 15:23:52
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An exploration of surface enhanced Raman spectroscopy (SERS) for in situ detection of sulfite under high pressure
摘要： In this work, silver nanoparticles film was directly fabricated on the surface of the diamond anvil as SERS active substrate for the first time by using a simple and convenient method. With this approach, the SERS spectrum of sulfite was obtained with a detection limit of 5 μmol/L in diamond anvil cell (DAC) at ～50 MPa. The SERS signal intensity of the two main vibration modes, νsymSeO and δsymOeSeO, showed good linearity with the Na2SO3 concentrations in the range from 5 to 40 μmol/L under high pressure. The linear correlation coefficients were 97.67% and 96.08%, respectively. The effects of pressure on the SERS intensity and Raman shift of the two modes were also studied. The SERS intensity dropped with the increase of pressure and the two main vibration modes shifted to high wave-number when the pressure increased in the pressures ranging from 54 MPa to 330 MPa. The experiments indicate that this method is rapid, convenient and sensitive in detecting sulfite at high pressures. It can be developed as an effect in situ method to detect sulfite in the process of high pressure reaction.
关键词： SERS,In situ,High pressure,Diamond-anvil cell,Sulfite
更新于2025-09-23 15:23:52