Prone Positioning for ARDS. still misunderstood and misused

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by a non-cardiogenic pulmonary edema with bilateral chest X-ray opacities and hypoxemia refractory to oxygen therapy and low level of positive end-expiratory pressure (1). Recently, a large observational study reported an ARDS prevalence of 10.4% of all ICU admissions and of 23.4% of all subjects receiving mechanical ventilation (2). Despite these alarming numbers, according to the most recent literature, ARDS is still under-recognized, undertreated, and associated with a mortality rate that in the most severe forms is close to 50% (2)

Stokes drift for inertial particles transported by water waves

We study the effect of surface gravity waves on the motion of inertial particles in an incompressible fluid. Using the multiple-scale technique, we perform an analytical calculation which allows us to predict the dynamics of such particles; results are shown for both the infinite- and finite-depth regimes. Numerical simulations based on the velocity field resulting from the second-order Stokes theory for the surface elevation have been performed, and an excellent agreement with the analytical predictions is observed. Such an agreement seems to hold even beyond the formal applicability of the theory. We find that the presence of inertia leads to a non-negligible correction to the well-known horizontal Stokes drift; moreover, we find that the vertical velocity is also affected by a drift. The latter result may have some relevant consequences on the rate of sedimentation of particles of finite size. We underline that such a drift would also be observed in the (hypothetical) absence of the gravitational force.Comment: 9 pages, 4 figure

Stability Enhancement for Single-Loop Voltage Controlled Voltage-Source Converters with LC-Filter

Voltage controlled voltage source converters (VSCs) have been widely applied in microgrids, uninterruptible power sources, smart transformer and 400 Hz ground power units for airplanes, etc. An LC filter is generally adopted to attenuate high frequency switching harmonic and to improve the qualities of output voltage and current for grid or loads. Nevertheless, VSCs have to trade-off between the stability characteristic and the ability of switching harmonics suppression when a single-loop voltage control method is adopted. In general, the resonant frequency ω r of LC filter should be less than 1/4 of sampling frequency ω s to ensure sufficient attenuation of the switching harmonic. However, ω r should be higher than 1/3 of ω s for the system stability when a proportional-resonant (PR) controller with a positive proportional gain is implemented. This paper proposes a feedback of modulation voltage (FMV) control design method for single-loop control to ensure stability condition in a higher frequency range and good switching harmonics suppression at the same time. Finally, simulation results are provided to verify the effectiveness of the proposed method

What drives the growth of start-up firms? A tool for mapping the state-of-the-art of the empirical literature

Purpose – This study aims to enrich the current theoretical debate on the growth of start-up firms by extensively investigating the ongoing empirical studies in this research stream. Moreover, this study identifies drivers whose support roles are confirmed in the literature and recommends further research opportunities. Design/methodology/approach – In this study, we analysed the results of 316 empirical studies on start-up firms and growth and also identified and categorised 66 growth drivers. We presented these drivers in three- dimensional charts: 1) the frequency of using each driver in the 316 studies, 2) the consistency of each driver as measured by the number of studies supporting its statistical significance and 3) the net effect (positive or negative) of each driver on growth. Findings – Our analysis compares extant studies on growth drivers and shows some under-explored growth factors of start-up firms. Practical implications – Both start-up managers and policymakers can benefit from this study. This study provided managers with a fine-grained tool on the main growth drivers and can guide policymakers in supporting policies for start-up firms. Originality/value – This study provides a rich, fine-grained and coherent picture of several potential growth drivers of start-up firms. Moreover, we extended our analysis to various potential drivers more than previous studies on this topic, thereby providing fruitful insights into the critical growth factors for start-up firms

Secure Platform Over Wireless Sensor Networks

Life sciences: general issue

A note on the Kuramoto-Sivashinsky equation with discontinuity

In this work we consider differential equations of the type $$pm, u^{(k)}=f(u),$$ and study the extinction profile of their solutions. Emphasis is placed on the special case $-u^{(4)}=sign(u)$, which is related to the Kuramoto-Sivashinsky equation. In this case we describe in more detail the extinction phenomenon and prove a conjecture by Galaktionov and Svirshchevskii

Space Vector Modulation Technique for Reducing Harmonics in Current with Zero Common-Mode Voltage for Two-Parallel Three-Level Converters

A zero common-mode voltage (ZCMV) modulation has the advantage of reducing electromagnetic interference (EMI) and a feature that hardly generates a zero- sequence circulating current (ZSCC) in converters operating in parallel. However, this modulation has a critical issue related to the increase in harmonics in the phase current due to the limitation of using voltage vectors generating ZCMV. Thus, this paper proposes an optimal space vector modulation (SVM) technique for two-parallel three-level converters to reduce the harmonics increased by using the ZCMV PWM. The creation of virtual voltage vectors (VVVs) using vector synthesis based on the ZCMV PWM is addressed. Accordingly, new small regions in each sector of the SVM are defined in consideration with the nearest three voltage vectors, including the virtual vectors. In addition, PWM sequences for each region and dwell time for each voltage vector are also determined. Optimal vector utilization of the proposed ZCMV SVM can further reduce the current harmonics. The performance comparison between the proposed ZCMV SVM and existing methods are presented in simulation and experimental results

Enhanced Current-Type P-HIL Interface Algorithm for Smart Transformers Testing

The energy systems are evolving towards the wide integration of power electronics-based technologies, such as electric vehicles. A promising solution to increase the grid controllability is represented by grid-forming converters, such as smart transformers (STs). Being a new technology, the ST experimental testing is a fundamental step before commercialization. Instead of performing time consuming and not flexible on-field tests, the Power Hardware In the Loop (P-HIL) offers a flexible testing environment for experimentally validating new technologies. The real-time simulation of the electrical grid offers the possibility to vary quickly the testing environment, while the power amplification stage offers the validation of the real hardware. Despite the clear testing advantages, the P-HIL stability and testing accuracy is still a matter of study. This paper introduces a new P-HIL interface approach for ST application, that can guarantee high testing accuracy in a large frequency spectrum. The proposed approach combines the tracking capability of the existing controlled Current-Type P-HIL interface algorithm, with the well-known Partial Circuit Duplication approach. The accuracy and stability analysis has been performed analytically and validated by means of extensive experimental P-HIL testing

Reduction of the Circulating Current among Parallel NPC Inverters

In medium/high power applications including smart transformers, active power filters and wind turbines, 3-level Neutral-Point-Clamped (NPC) inverters proved to be a reliable solution, providing high efficiency and low harmonic distortion. In practice, several NPCs are parallel connected and operated in interleaved to further increase the power handling and reduce the line filters size. However, if such configuration has a common dc-link, High-frequency Zero-Sequence Circulating-Current (HF-ZSCC) arises among the inverters, increasing power losses of the switching devices and propagating the stress on the dc-capacitors. Moreover, the amplitude of the HF-ZSCC is inversely proportional to the filter inductance size, therefore in real applications it can reach hundreds of Amperes even with relatively low output currents. The research on the HF-ZSCC is mostly concentrated on 2-level inverters for low voltage grids and traction applications, where the inductance size is relatively big and the HF-ZSCC does not affect the system efficiency. Differently, NPCs provide higher switching degree of freedom and more sophisticated methods can be applied to reduce the HF-ZSCC. This paper investigates a Double-Reference Pulse-Width Modulation (DRPWM) as solution for diminishing the HF-ZSCC in paralleled NPCs. The performance of DRPWM method is confirmed by both simulation and experiments, performed on a 1.6MVA system

Integration and Optimization of Voltage Active Filtering Functionality in a PV Park

The stringent regulations on the power quality declared in the standard IEEE 519-2014 push the companies and the power producers to install active filters to compensate the voltage harmonics distortion in the point of common coupling (PCC). However, in the case of a Photovoltaic (PV) park, the cost for an additional active filter converter can be saved by using the PV converters themselves as active filter. This solution is very attractive, but reserves several challenges. In fact, the harmonic current injection by the PV converters can generate ripples in the DC link which increases the stress on the converter components and affects the MPPT. Moreover, the overcurrent protection of the PV converter must be taken into account. In this paper a centralized optimized strategy to share the harmonic current injection among all the converters in a PV park is investigated. The optimization is formulated as a quadratic programming (QP) problem: the active power consumed by the PV park for the active filtering and the DC link ripple of the PV converters caused by the harmonic currents injection are minimized. The limit on the maximum injectable harmonic current by each PV converter are respected