A two-way 224-Gbit/s PAM4-based fibre-FSO converged system

A two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4)-based fibre-free-space optical (FSO) converged system through a 25-km single-mode fibre (SMF) transport with 500-m free-space transmission is successfully constructed, which adopts injection-locked vertical-cavity surface-emitting lasers with polarisation-multiplexing mechanism for a demonstration. Compared with one-way transmission, two-way transmission is an attractive architecture for fibre-FSO converged system. Two-way transmission over SMF transport with free-space transmission not only reduces the required number of fibres and the setups of free-space transmission, but also provides the advantage of capacity doubling. Incorporating dual-wavelength four-level pulse amplitude modulation (PAM4) modulation with polarisation-multiplexing mechanism, the transmission capacity of fibre-FSO converged system is significantly enhanced to 224 Gbit/s (56 Gbit/s PAM4/wavelength × 2-wavelength × 2-polarisation) for downlink/uplink transmission. Bit error rate and PAM4 eye diagrams (downstream/upstream) perform well over 25-km SMF transport with 500-m free-space transmission. This proposed two-way fibre-FSO converged system is a prominent one not only because of its development in the integration of fibre backbone with optical wireless extension, but also because of its advantage in two-way transmission for affording high downlink/uplink data rate with good transmission performance.

Sex features of cutaneous microvasculature in healthy working-age people

Aim. To study sex characteristics of cutaneous microvascular structure and function in a cohort of healthy working-age people without cardiovascular diseases.Material and methods. The study included 35 healthy men (42±4 years) and 34 women (41 ±5 years). The cardiovascular system was assessed in all patients. The microcirculatory bed of the skin was investigated by the following non-invasive methods: 1) computerized video capillaroscopy; 2) laser Doppler flowmetry; 3) photoplethysmography.Results. According to computerized video capillaroscopy in men, compared with women, there was a smaller number of both functioning capillaries (78 vs 86 capillaries/mm2, respectively (p<0,05)) and their total number (100 vs 120 capillaries/mm2, respectively (p<0,001)). Against the background of a decrease in capillary density in men, there was a higher skin interstitial hydration — 113 vs 96 gm (p<0,005) in men than in women. At the level of precapillary arterioles, where humoral tone regulation prevails. Laser Doppler flowmetry revealed lower pulse amplitude in men than in women — 0,87 vs 1,02 pf, respectively (p<0,05), which indicates a lower arterial blood inflow to exchange microvessels. Against this background, the constrictor response of precapillary arterioles to a sympathetic nervous system stimulation in men is higher than in women — 45% vs 40%, respectively (p<0,05). At the level of large arterioles, where neural tone regulation prevails, photoplethysmography revealed lower augmentation index standardized at a heart rate in men (-4,6 vs 1,7%, respectively, p<0,05), which indicates lower rigidity of muscular vessels in men.Conclusion. In working-age healthy people, sex differences are noted at all cutaneous microvascular levels, which must be taken into account when planning studies.

A conceptual model for changes in finger photoplethysmograph signals caused by hand posture and isothermic regulation

Objective. To observe changes in baseline and pulsatile light absorbance (photoplethysmograph, PPG) in the finger-tip, by raising the hand above the horizontal plane in recumbent subjects. We applied current knowledge of the circulation to the finger-tip, particularly arteriovenous anastomoses (AVAs), and the physiology of the venous circulation. Approach. We studied healthy young volunteers in a quiet thermoneutral environment. A finger plethysmograph on the non-dominant hand recorded transmission of red and infra-red light, and the values were converted into absorbance to allow comparisons within and between subjects. Breathing movements were recorded unobtrusively to assess any effect on absorbance and the pulse amplitude of the signals. All body movements were passive: the study arm was elevated in a trough to about 40° above the horizontal plane. The following conditions were studied, each for 15 minutes, using the last 10 minutes for analysis: recumbent, study arm elevated, study arm horizontal, and both legs elevated by 40°. Main results. There was a substantial time-related effect, and considerable variation between subjects. Arm elevation reduced red light absorbance and increased the range of amplitudes of the PPG waveform: only in subjects with large absorbances, did waveform amplitude increase. The other main effect was that spontaneous, thermoregulatory decreases in absorbance were associated with decreases in waveform amplitude. Significance. Finger-tip vessels distend with blood when AVAs open. The vessels pulsate more strongly if venous collapse allows the vessels to become more compliant. The postcapillary circulation is likely to be an important source of pulsation.

Intercompartmental communication between the cerebrospinal and adjacent spaces during intrathecal infusions in an acute ovine in-vivo model

Introduction The treatment of hydrocephalus has been a topic of intense research ever since the first clinically successful use of a valved cerebrospinal fluid shunt 72 years ago. While ample studies elucidating different phenomena impacting this treatment exist, there are still gaps to be filled. Specifically, how intracranial, intrathecal, arterial, and venous pressures react and communicate with each other simultaneously. Methods An in-vivo sheep trial (n = 6) was conducted to evaluate and quantify the communication existing within the cranio-spinal, arterial, and venous systems (1 kHz sampling frequency). Standardized intrathecal infusion testing was performed using an automated infusion apparatus, including bolus and constant pressure infusions. Bolus infusions entailed six lumbar intrathecal infusions of 2 mL Ringer’s solution. Constant pressure infusions were comprised of six regulated pressure steps of 3.75 mmHg for periods of 7 min each. Mean pressure reactions, pulse amplitude reactions, and outflow resistance were calculated. Results All sheep showed intracranial pressure reactions to acute increases of intrathecal pressure, with four of six sheep showing clear cranio-spinal communication. During bolus infusions, the increases of mean pressure for intrathecal, intracranial, arterial, and venous pressure were 16.6 ± 0.9, 15.4 ± 0.8, 3.9 ± 0.8, and 0.1 ± 0.2 mmHg with corresponding pulse amplitude increases of 2.4 ± 0.3, 1.3 ± 0.3, 1.3 ± 0.3, and 0.2 ± 0.1 mmHg, respectively. During constant pressure infusions, mean increases from baseline were 14.6 ± 3.8, 15.5 ± 4.2, 4.2 ± 8.2, and 3.2 ± 2.4 mmHg with the corresponding pulse amplitude increases of 2.5 ± 3.6, 2.5 ± 3.0, 7.7 ± 4.3, and 0.7 ± 2.0 mmHg for intrathecal, intracranial, arterial, and venous pulse amplitude, respectively. Outflow resistances were calculated as 51.6 ± 7.8 and 77.8 ± 14.5 mmHg/mL/min for the bolus and constant pressure infusion methods, respectively—showing deviations between the two estimation methods. Conclusions Standardized infusion tests with multi-compartmental pressure recordings in sheep have helped capture distinct reactions between the intrathecal, intracranial, arterial, and venous systems. Volumetric pressure changes in the intrathecal space have been shown to propagate to the intraventricular and arterial systems in our sample, and to the venous side in individual cases. These results represent an important step into achieving a more complete quantitative understanding of how an acute rise in intrathecal pressure can propagate and influence other systems.

The Human Dive Reflex During Consecutive Apnoeas in Dry and Immersive Environments: Magnitude and Synchronicity

Introduction: The human dive reflex (HDR), an O2 conserving reflex, is characterised by an interplay of central parasympathetic and peripheral sympathetic reactions, which are presumed to operate independently of each other. The HDR is fully activated during apnoea with facial immersion in water and complete immersion in water is thought to increase the magnitude of HDR during consecutive apnoeas. A comparison of HDR activity between consecutive apnoeas in full-body immersion with consecutive apnoeas in dry conditions has not been fully explored. Also, the interplay between parasympathetic and sympathetic reactions involved in the HDR has not been thoroughly analysed.Methods: 11 human volunteers performed 3 consecutive 60 s apnoeas with facial immersion in dry conditions (FIDC) and 3 consecutive apnoeas with facial immersion in full immersion (FIFI). Heart rate (HR), R-R interval (RRI), finger pulse amplitude (FPA), splenic width (SW) and SpO2 were all measured before, during and after apnoeas. A one-way ANOVA using Dunn’s post hoc test was performed to assess HDR activity, and a Pearson’s correlation test was performed to assess HDR synchronisation between physiological parameters during both conditions.Results: Although HDR activity was not significantly different between both conditions, HR and RRI showed progressively greater changes during FIFI compared with FIDC, while SW and FPA changes were relatively equivalent. During FIDC, significant correlations were found between SW &amp; SpO2 and FPA &amp; SpO2. During FIFI, significant correlations were found between RRI &amp; FPA, SW &amp; FPA, HR &amp; SpO2 and FPA &amp; SpO2.Discussion: While there was no significant difference found between HDR activity during FIDC and FIFI, consecutive apnoeas during FIFI triggered a greater magnitude of cardiac activity. Furthermore, significant correlations between RRI and SW with FPA indicate a crosstalk between parasympathetic tone with splenic contraction and increased peripheral sympathetic outflow during FIFI compared to FIDC. In conclusion, HDR activity during consecutive apnoeas does not differ between FIDC and FIFI. There appears to be however a greater level of synchronicity during apnoeas in FIFI compared to FIDC and that this is most likely due to the physiological effects of immersion, which could induce neural recruitment and increased cross talk of HDR pathways.

Pragmatic method for fast programming of hybrid photon counting detectors

It is now been over 15 years since Hybrid Photon Counting Detectors (HPCD) became one of the standard position-sensitive detectors for synchrotron light sources and X-ray detection applications. This is mainly due to their single-photon sensitivity over a high dynamic energy range and electronic noise suppression thanks to energy thresholding. To reach those performances, all HPCD pixels must feature the same electrical response against photons of the same energy. From the analysis of a monochromatic beam, in case of an ideal HPCD detector, it would be sufficient to apply a fixed voltage threshold among all pixels, positioned at half of the mean pulse amplitude to count every photon above the threshold. However, in practical cases, it must be considered that noise baselines from all pixels are not always strictly located at the same voltage level but can be spread over some voltage ranges. To address this kind of issue, most of all HPCDs apply a conventional threshold equalization method, that mainly relies on three steps; the setting of a global threshold at an arbitrary value, the identification of pixels noise baseline around that global threshold through an in-pixel threshold trimmer, and the computation of the required threshold offsets for setting all pixels at their own noise baseline at the same time. However, in case of a first-time use of an HPCD prototype, the threshold equalization might be biased by parameters that are wrongly set. Those biases can sometimes be characterized by the inability to localize some pixel noise baselines, which could be outside the voltage range of the threshold trimmer. The recovery of those biased pixels could be performed by changing the position of the global threshold, or by increasing the voltage range of the threshold trimmer. Unfortunately, both solutions could be time consuming due to the lack of information on the required steps for recovering all noise baselines. In order to overcome this issue in a reasonable time, this work introduces a pragmatic method that can be applied to HPCDs for an early and effective identification of appropriate pixels’ parameters, avoiding the need to test a high number of pixels configurations. The application of this method, at the early stage of the HPCD calibration, may drastically reduce the investigation time for finding the optimal operating parameters of HPCD prototypes.

Effect of Pulsed Jet on Pore Pressure of Deep Formation Rock

Pulsed jet significantly affects the pore pressure of deep formation and then affects the mechanical ROP. In this paper, the effect of jet pulsation on deep pore pressure in the formation is studied by the finite element method. Under the pulsed jet, the maximum relative negative pressure is along the wellbore axis, and the farther it is to the borehole axis, the smaller the relative negative pressure is. With the increase of pulse frequency, the relative negative pressure increases and the maximum point of relative negative pressure moves upward. The optimum pulse frequency is from 50 Hz to 500 Hz. There is a linear relationship between pulse amplitude and relative negative pressure.

Turbocharger Radial Turbine Response to Pulse Amplitude

Under on-engine operating conditions, a turbocharger turbine is subject to a pulsating flow and, consequently, experiences deviations from the performance measured in gas-stand flow conditions. Furthermore, due to the high exhaust gases temperatures, heat transfer further deteriorates the turbine performance. The complex interaction of the aerothermodynamic mechanisms occurring inside the hot-side, and consequently the turbine behavior, is largely affected by the shape of the pulse, which can be parameterized through three parameters: pulse amplitude, frequency, and temporal gradient. This paper investigates the hot-side system response to the pulse amplitude via Detached Eddy Simulations (DES) of a turbocharger radial turbine system including exhaust manifold. Firstly, the computational model is validated against experimental data obtained in gas-stand flow conditions. Then, two different mass flow pulses, characterized by a pulse amplitude difference of 5%, are compared. An exergy-based post-processing approach shows the beneficial effects of increasing the pulse amplitude. An improvement of the turbine power by 1.3%, despite the increment of the heat transfer and total internal irreversibilities by 5.8% and 3.4\%, respectively, is reported. As a result of the higher maximum speeds, internal losses by viscous friction are responsible for the growth of the total internal irreversibilities as pulse amplitude increases.

Submergence of the filamentous Zygnematophyceae Mougeotia induces differential gene expression patterns associated with core metabolism and photosynthesis

The streptophyte algal class Zygnematophyceae is the closest algal sister lineage to land plants. In nature, Zygnematophyceae can grow in both terrestrial and freshwater habitats and how they do this is an important unanswered question. Here, we studied what happens to the zygnematophyceaen alga Mougeotia sp., which usually occurs in permanent and temporary freshwater bodies, when it is shifted to liquid growth conditions after growth on a solid substrate. Using global differential gene expression profiling, we identified changes in the core metabolism of the organism interlinked with photosynthesis; the latter went hand in hand with measurable impact on the photophysiology as assessed via pulse amplitude modulation (PAM) fluorometry. Our data reveal a pronounced change in the overall physiology of the alga after submergence and pinpoint candidate genes that play a role. These results provide insight into the importance of photophysiological readjustment when filamentous Zygnematophyceae transition between terrestrial and aquatic habitats.

Trabecular Meshwork Motion Profile from Pulsatile Pressure Transients: A New Platform to Simulate Transitory Responses in Humans and Nonhuman Primates

Trabecular meshwork (TM) motion abnormality is the leading cause of glaucoma. With technique limitations, how TM moves is still an enigma. This study describes a new laboratory platform to investigate TM motion responses to ocular transients in ex vivo eyes. The anterior segments of human cadaver and primate eyes were mounted in a perfusion system fitting. Perfusion needles were placed to establish mean baseline pressure. A perfusion pump was connected to the posterior chamber and generated an immediate transient pressure elevation. A phase-sensitive optical coherent tomography system imaged and quantified the TM motion. The peak-to-peak TM displacements (ppTMD) were determined, a tissue relaxation curve derived, and a time constant obtained. This study showed that the ppTMD increased with a rise in the pulse amplitude. The ppTMD was highest for the lowest mean pressure of 16 mmHg and decreased with mean pressure increase. The pulse frequency did not significantly change ppTMD. With a fixed pulse amplitude, an increase in mean pressure significantly reduced the time constant of recoil from maximum distension. Our research platform permitted quantitation of TM motion responses to designed pulse transients. Our findings may improve the interpretation of new TM motion measurements in clinic, aiding in understanding mechanisms and management.