In situ Near-Ambient Pressure X-ray Photoelectron Spectroscopy Reveals the Influence of Photon Flux and Water on the Stability of Halide Perovskite.

For several years, scientists have been trying to understand the mechanisms that reduce the long-term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3 NH3 PbI3 perovskite films and solar cells using in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), field emission scanning electron microscopy (FESEM), and current density-voltage (J-V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP-XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J-V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J-V sweeps.

Placebo-controlled biofeedback blood pressure effect in hypertensive humans.

The role of biofeedback in blood pressure control remains ill-defined because of nonspecific (placebo) effects, small study numbers, and the technical limitations of continuous pressure feedback. Clarification of its potential is awaited by those seeking a nonpharmacological approach to blood pressure control. This study examines the capability for systolic pressure lowering of 5 mm Hg or more using continuous pressure feedback in a statistical sample of untreated, well-characterized, mildly hypertensive individuals. Subjects were randomized in a double-blind study to active or placebo biofeedback. Placebo consisted of a modified contingency approach, using a partial disguise based on a digital high pass filter with 15 elements. Blood pressure-lowering capability was assessed during two laboratory sessions. Continuous visual feedback resulted in 11 of 28 subjects on active treatment and 12 of 28 on placebo treatment lowering their systolic pressure by 5 mm Hg or more (11 +/- 5.6 and 12 +/- 8.4 mm Hg, respectively; P = NS). Prestudy pressure was well-matched (153 +/- 9/97 +/- 4 and 154 +/- 8/98 +/- 4 mm Hg, respectively). An initial small difference in diurnal profile did not change. These findings indicate that among mildly hypertensive individuals, almost half can lower systolic pressure at will for short periods. This capability is independent of the real or placebo nature of the feedback signal. We conclude that there is no specific short-term biofeedback pressure-lowering capability in hypertensive individuals. Further exploration is needed to determine whether specific components of the placebo effect can be delineated, whether personality characteristics influence the response, and whether further biofeedback training can alter the outcome.

The effect of induced reflections on human arterial waveforms.

1. External compression of the human brachial artery results in waveform reflection. 2. Resonant waves are found superimposed on the original blood pressure signal. 3. The mechanism may be likened to the operation of an organ pipe with reflections at both ends of an arterial segment. 4. This has implications for measurements in arteries where external pressure is applied.

Quantitative photoplethysmography: Lambert-Beer law or inverse function incorporating light scatter.

Finger blood volume is commonly determined from measurement of infra-red (IR) light transmittance using the Lambert-Beer law of light absorption derived for use in non-scattering media, even when such transmission involves light scatter around the phalangeal bone. Simultaneous IR transmittance and finger volume were measured over the full dynamic range of vascular volumes in seven subjects and outcomes compared with data fitted according to the Lambert-Beer exponential function and an inverse function derived for light attenuation by scattering materials. Curves were fitted by the least-squares method and goodness of fit was compared using standard errors of estimate (SEE). The inverse function gave a better data fit in six of the subjects: mean SEE 1.9 (SD 0.7, range 0.7-2.8) and 4.6 (2.2, 2.0-8.0) respectively (p < 0.02, paired t-test). Thus, when relating IR transmittance to blood volume, as occurs in the finger during measurements of arterial compliance, an inverse function derived from a model of light attenuation by scattering media gives more accurate results than the traditional exponential fit.

Relevance of the waterfall phenomenon in continuous finger cuff blood pressure measurements.

1. Finger cuff blood pressure monitors that provide continuous presentation of arterial pressure at the finger are available. 2. The operation of such instruments is based on 'clamping' arterial volume under a pressurized encircling cuff applied to a digit. Blood volume is detected by measuring infra-red transmission across the finger. 3. The compressed veins adopt cuff pressure and combine with the resistance of the peripheral vascular bed at the finger tip to control the blood flow. This results in waterfall behaviour in the veins under the cuff. 4. With the cuff set just 5 mmHg below the undisturbed arterial pressure, adequate flow to the distal finger is maintained. 5. Two potential sources of error affect the finger cuff blood pressure method. These are related to the increase in systolic pressure associated with moving peripherally and the variable value of occluding transmural pressure, both of which depend on muscular tone.

[Determination of cyclamate in complex matrix using HPLC after column derivatization with 4-fluoro-7-nitrobenzofurazan]. / Bestimmung von Cyclamat in komplexer Matrix mittels HPLC nach Vorsäulenderivatisierung mit 4-Fluoro-7-nitrobenzofurazon.

A method for the analysis of cyclamate in complex foodstuffs has been developed. This method is applicable in strongly coloured and protein-rich foodstuffs. The quantitative determination depends on oxidation of cyclamate to cyclohexylamine and derivatisation with 4-fluoro-7-nitrobenzofuran (NBD-F). The derivatives are analysed by HPLC on a C18: reversed-phase column, their minimal stability being 12 h. There are two possible methods of detection: (a) absorbance at 485 nm and (b) fluorescence with excitation at 485 nm and emission at 530 nm. The detection limit of cyclamate is 5 mg/kg foodstuff, with fluorescence detection 0.4 mg/kg. The recoveries are in the range of 88% to 104%.