Self-Powered Point-of-Care Device for Galvanic Cell-Based Sample Concentration Measurement

A novel self-powered point-of-care low-power electronics approach for galvanic cell-based sample concentration measurement is presented. The electronic system harvests and senses at the same time from the single cell. The system implements a solution that is suitable in those scenarios where extreme low power is generated from the fuel cell. The proposed approach implements a capacitive-based method to perform a non-linear sweep voltammetry to the cell, but without the need to implement a potentiostat amplifier for that purpose. It provides a digital-user readable result without the need for external non-self-powered devices or instruments compared with other solutions. The system conception was validated for a particular case. The scenario consisted of the measurement of a NaCl solution as the electrolyte, which was related to the conductivity of the sample. The electronic reader continuously measured the current with a transfer function gain of 1.012 V mA−1. The overall system exhibited a maximum coefficient of variation of 6.1%, which was an improvement compared with the state-of-the-art. The proof of concept of this electronics system was validated with a maximum power consumption of 5.8 μW using commercial-off-the-self parts.

OPTIMALISASI RESISTANSI FEEDBACK DAN RESISTANSI INPUT PADA PENGUAT INVERTING UNTUK PENGKONDISI SINYAL

Penguatan rangkaian penguat inverting dengan Op Amp ditentukan oleh nilai Resistansi Feedback (Rf) dan Resistansi Input (Rin) dimana penguatan merupakan perbandingan antara Rf dan Rin. Biasanya salah satu nilai (Rf atau Rin) diambil secara bebas. Secara teoritis formula tersebut memperbolehkan memberikan nilai Rf dan Rin berapapun asalkan memenuhi syarat kebutuhan penguatan (Av). Penentuan nilai yang bebas (berapapun) ini sering membingungkan karena secara teori semua nilai bisa diterapkan namun secara praktik dilapangan tidak semua nilai bisa memberikan hasil yang diharapkan. Untuk menghilangkan kebingungan dalam memilih nilai Rf dan Rin yang memenuhi maka perlu ditentukan satu nilai Optimal. Dengan penentuan Rf dan Rin optimal maka dalam satu perencanaan tidak ada nilai yang berbeda-beda dan dipastikan rangkaian penguat bekerja sesuai dengan fungsinya. Nilai Rf dan Rin optimal ditentukan oleh Resistansi Input deferensial (Rid) dan Resistansi Output (Ro) dari IC op Amp yang digunakan dan tergantung pula dengan fungsi alih (penguatan) dari Rangkaian yang direncanakan. Dengan nilai Rf optimal maka rangkaian penguat bisa bekerja dengan baik dan tidak terjadi perbedaan dalam pemilihan resistansi feedback maupun resistansi input. Strengthening the inverting amplifier circuit with the Op Amp is determined by the Feedback Resistance (Rf) and Input Resistance (Rin) where the gain is a comparison between Rf and Rin . Usually one value (Rf or Rin) is taken freely. Theoretically the formula allows giving any value of Rf and Rin as long as it meets the requirements for reinforcement requirements (Av). Determination of free value (whatever) is often confusing because in theory all values can be applied but practically in the field not all values can provide the expected results. To eliminate the confusion in choosing the value of Rf and Rin that meets the need to be determined one Optimal value. With the determination of Rf and Rin optimally in one plan there are no different values and it is certain that the amplifier circuit works according to its function. The optimal Rf and Rin values are determined by the Differential Input (Rid) Resistance and Output Resistance (Ro) of the IC op Amp used and depend also on the transfer function (gain) of the planned Circuit. With the optimal Rf value the amplifier circuit can work properly and there is no difference in the selection of feedback resistance or input resistance.

Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (−10, −20, and −30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02–0.30 Hz) and the intra-beat rapid change (0.78–9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07–0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during −20 and −30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance ( r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation ( P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07–0.20 Hz). NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

Dynamic cerebral autoregulation after bed rest: effects of volume loading and exercise countermeasures

This study assessed effects of head-down-tilt (HDT) bed rest on dynamic cerebral autoregulation (CA) in 21 healthy young adults with volume loading and exercise countermeasures. Of these, seven underwent an 18-day bed rest without exercise countermeasures ( sedentary group). Volume loading with dextran infusion was performed after bed rest to restore reduced plasma volume to levels before bed rest. In the other 14 subjects, supine cycling during bed rest was performed to preserve cardiac work from before bed rest ( exercise group). Volume loading was also performed in a subgroup of these subjects ( Ex+Dex, n = 7). Dynamic CA was estimated by transfer function analysis of changes in arterial pressure and cerebral blood flow (CBF) velocity in the very low (VLF, 0.02–0.07 Hz), low (LF, 0.07–0.20 Hz), and high frequency ranges (HF, 0.20–0.35 Hz). After bed rest, transfer function gain was reduced in the sedentary group (VLF, 0.93 ± 0.23 to 0.61 ± 0.23 cm−1·s−1·mmHg; P = 0.007) and in the exercise group (LF, 1.22 ± 0.43 to 0.94 ± 0.26 cm−1·s−1·mmHg; P = 0.005, HF, 1.32 ± 0.55 to 1.00 ± 0.32 cm−1·s−1·mmHg; P = 0.010). After volume loading, transfer function gain increased in the sedentary group but not in the Ex+Dex group. Taken together, these findings suggest that dynamic CA was preserved or improved after HDT bed rest in both sedentary and exercise subjects. Furthermore, increases of transfer function gain with volume loading suggest that changes in plasma volume may play an important role in CBF regulation.

Interaction Between Swirl Number Fluctuations and Vortex Shedding in a Single-Nozzle Turbulent Swirling Fully-Premixed Combustor

Flame response to imposed velocity fluctuations is experimentally measured in a single-nozzle turbulent swirling fully-premixed combustor. The flame transfer function is used to quantify the flame's response to imposed velocity fluctuations. Both the gain and phase of the flame transfer function are qualitatively similar for all operating conditions tested. The flame transfer function gain exhibits alternating regions of decreasing gain with increasing forcing frequency followed by regions of increasing gain with increasing forcing frequency. This alternating behavior gives rise to gain extrema. The flame transfer function phase magnitude increases quasi-linearly with increasing forcing frequency. Deviations from the linear behavior occur in the form of inflection points. Within the field, the current understanding is that the flame transfer function gain extrema are caused by the constructive/destructive interference of swirl number fluctuations and vortex shedding. Phase-synchronized images of forced flames are acquired to investigate the presence/importance of swirl number fluctuations, which manifest as fluctuations in the mean flame position and vortex shedding in this combustor. An analysis of phase-synchronized flame images reveals that mean flame position fluctuations are present at forcing frequencies corresponding to flame transfer function gain minima but not at forcing frequencies corresponding to flame transfer function gain maxima. This observation contradicts the understanding that flame transfer function gain maxima are caused by the constructive interference of mean flame position fluctuations and vortex shedding, since mean flame position fluctuations are shown not to exist at flame transfer function gain maxima. Further analysis of phase-synchronized flame images shows that the variation of the mean flame position fluctuation magnitude with forcing frequency follows an inverse trend to the variation of flame transfer function gain with forcing frequency, i.e., when the mean flame position fluctuation magnitude increases, the flame transfer function gain decreases and vice versa. Based on these observations it is concluded that mean flame position fluctuations are a subtractive effect. The physical mechanism through which mean flame position fluctuations decrease flame response is through the interaction of the flame with the Kelvin–Helmholtz instability of the mixing layer in the combustor. When mean flame position fluctuations are large the flame moves closer to the mixing layer and damps the Kelvin–Helmholtz instability due to the increased kinematic viscosity, fluid dilatation, and baroclinic production of vorticity with the opposite sign associated with the high temperature reaction zone.

Interaction Between Swirl Number Fluctuations and Vortex Shedding in a Single-Nozzle, Turbulent, Swirling, Fully-Premixed Combustor

Flame response to imposed velocity fluctuations is experimentally measured in a single-nozzle, turbulent, swirling, fully-premixed combustor. The flame transfer function is used to quantify the flame’s response to imposed velocity fluctuations. Both the gain and phase of the flame transfer function are qualitatively similar for all operating conditions tested. Flame transfer function gain exhibits alternating regions of decreasing gain with increasing forcing frequency followed by regions of increasing gain with increasing forcing frequency. This alternating behavior gives rise to gain extrema. Flame transfer function phase magnitude increases quasi-linearly with increasing forcing frequency. Deviations from the linear behavior occur in the form of inflection points. Within the field, the current understanding is that the flame transfer function gain extrema are caused by the constructive/destructive interference of swirl number fluctuations and vortex shedding. Phase-synchronized images of forced flames are acquired to investigate the presence/importance of swirl number fluctuations, which manifest as fluctuations in mean flame position, and vortex shedding in this combustor. Analysis of phase-synchronized flame images reveals that mean flame position fluctuations are present at forcing frequencies corresponding to flame transfer function gain minima but not at forcing frequencies corresponding to flame transfer function gain maxima. This observation contradicts the understanding that flame transfer function gain maxima are caused by the constructive interference of mean flame position fluctuations and vortex shedding since mean flame position fluctuations are shown not to exist at flame transfer function gain maxima. Further analysis of phase-synchronized flame images shows that the variation of mean flame position fluctuation magnitude with forcing frequency follows an inverse trend to the variation of flame transfer function gain with forcing frequency, i.e. when mean flame position fluctuation magnitude increases flame transfer function gain decreases and vice versa. Based on these observations it is concluded that mean flame position fluctuations are a subtractive effect. The physical mechanism through which mean flame position fluctuations decrease flame response is through the interaction of the flame with the Kelvin-Helmholtz instability of the mixing layer in the combustor. When mean flame position fluctuations are large the flame moves closer to the mixing layer and damps the Kelvin-Helmholtz instability due to the increased kinematic viscosity, fluid dilatation, and baroclinic production of vorticity with opposite sign associated with the high temperature reaction zone.

Development of a Flame Transfer Function Framework for Transversely Forced Flames

This paper describes a framework for the development of a flame transfer function for transversely forced flames. While extensive flame transfer function measurements have been made for longitudinally forced flames, the disturbance field characteristics governing the flame response of a transversely forced flame are different enough to warrant separate investigation. In this work, we draw upon previous investigations of the flame disturbance pathways in a transversely forced flame to describe the underlying mechanisms that govern the behavior of the flame transfer function. Previous transverse forcing studies have shown that acoustic coupling in the nozzle region can result in both transverse and longitudinal acoustic fluctuations at the flame, and that the acoustic coupling is a function of combustor geometry, and hence, frequency. The results presented here quantify this coupling across a large range of frequencies using a velocity transfer function, FTL. The shape of the velocity transfer function gain indicates that there is strong acoustic coupling between the main combustor section and the nozzle at certain frequencies. Next, measured flame transfer functions are compared with results from theory. These theoretical results are derived from two level-set models of flame response to velocity disturbance fields, where velocity inputs are derived from experimental results. Data at several test conditions are presented and larger implications of this research are described with respect to gas turbine combustor design.

Differential effects of mild central hypovolemia with furosemide administration vs. lower body suction on dynamic cerebral autoregulation

Diuretic-induced mild hypovolemia with hemoconcentration reportedly improves dynamic cerebral autoregulation, whereas central hypovolemia without hemoconcentration induced by lower body negative pressure (LBNP) has no effect or impairs dynamic cerebral autoregulation. This discrepancy may be explained by different blood properties, by degrees of central hypovolemia, or both. We investigated the effects of equivalent central hypovolemia induced by furosemide administration or LBNP application on dynamic cerebral autoregulation to test our hypothesis that mild central hypovolemia due to furosemide administration enhances dynamic cerebral autoregulation in contrast to LBNP. Seven healthy male subjects received 0.4 mg/kg furosemide and LBNP, with equivalent decreases in central venous pressure (CVP). Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis between beat-to-beat mean arterial blood pressure (MAP) and mean cerebral blood flow velocity (MCBFV). CVP decreased by ∼3–4 mmHg with both furosemide administration (∼26 mg) and LBNP (approximately −20 mmHg). Steady state MCBFV remained unchanged with both techniques, whereas MAP increased significantly with furosemide administration. Coherence and transfer function gain in the low and high frequency ranges with hypovolemia due to furosemide administration were significantly lower than those due to LBNP (ANOVA interaction effects, P < 0.05), although transfer function gain in the very low frequency range did not change. Our results suggest that although the decreases in CVP were equivalent between furosemide administration and LBNP, the resultant central hypovolemia differentially affected dynamic cerebral autoregulation. Mild central hypovolemia with hemoconcentration resulting from furosemide administration may enhance dynamic cerebral autoregulation compared with LBNP.