Search

Mindfulness witnessed a substantial popularity surge in the past decade, especially as digitally self-administered interventions became available at relatively low costs. Yet, it is uncertain whether they effectively help reduce stress. In a preregistered (OSF https://doi.org/10.17605/OSF.IO/UF4JZ ; retrospective registration at ClinicalTrials.gov NCT06308744 ) multi-site study (n sites  = 37, n participants  = 2,239, 70.4% women, M age  = 22.4, s.d. age  = 10.1, all fluent English speakers), we experimentally tested whether four single, standalone mindfulness exercises effectively reduced stress, using Bayesian mixed-effects models. All exercises proved to be more efficacious than the active control. We observed a mean difference of 0.27 (d = -0.56; 95% confidence interval, -0.43 to -0.69) between the control condition (M = 1.95, s.d. = 0.50) and the condition with the largest stress reduction (body scan: M = 1.68, s.d. = 0.46). Our findings suggest that mindfulness may be beneficial for reducing self-reported short-term stress for English speakers from higher-income countries., (© 2024. The Author(s).)

Previously observed negative correlations between sample size and effect size (n-ES correlation) in psychological research have been interpreted as evidence for publication bias and related undesirable biases. Here, we present two studies aimed at better understanding to what extent negative n-ES correlations reflect such biases or might be explained by unproblematic adjustments of sample size to expected effect sizes. In Study 1, we analysed n-ES correlations in 150 meta-analyses from cognitive, organizational, and social psychology and in 57 multiple replications, which are free from relevant biases. In Study 2, we used a random sample of 160 psychology papers to compare the n-ES correlation for effects that are central to these papers and effects selected at random from these papers. n-ES correlations proved inconspicuous in meta-analyses. In line with previous research, they do not suggest that publication bias and related biases have a strong impact on meta-analyses in psychology. A much higher n-ES correlation emerged for publications' focal effects. To what extent this should be attributed to publication bias and related biases remains unclear., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Linden et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Meta-analyses typically quantify heterogeneity of results, thus providing information about the consistency of the investigated effect across studies. Numerous heterogeneity estimators have been devised. Past evaluations of their performance typically presumed lack of bias in the set of studies being meta-analysed, which is often unrealistic. The present study used computer simulations to evaluate five heterogeneity estimators under a range of research conditions broadly representative of meta-analyses in psychology, with the aim to assess the impact of biases in sets of primary studies on estimates of both mean effect size and heterogeneity in meta-analyses of continuous outcome measures. To this end, six orthogonal design factors were manipulated: Strength of publication bias; 1-tailed vs. 2-tailed publication bias; prevalence of p-hacking; true heterogeneity of the effect studied; true average size of the studied effect; and number of studies per meta-analysis. Our results showed that biases in sets of primary studies caused much greater problems for the estimation of effect size than for the estimation of heterogeneity. For the latter, estimation bias remained small or moderate under most circumstances. Effect size estimations remained virtually unaffected by the choice of heterogeneity estimator. For heterogeneity estimates, however, relevant differences emerged. For unbiased primary studies, the REML estimator and (to a lesser extent) the Paule-Mandel performed well in terms of bias and variance. In biased sets of primary studies however, the Paule-Mandel estimator performed poorly, whereas the DerSimonian-Laird estimator and (to a slightly lesser extent) the REML estimator performed well. The complexity of results notwithstanding, we suggest that the REML estimator remains a good choice for meta-analyses of continuous outcome measures across varied circumstances., Competing Interests: The authors have declared that no competing interests exist.

Heterogeneity emerges when multiple close or conceptual replications on the same subject produce results that vary more than expected from the sampling error. Here we argue that unexplained heterogeneity reflects a lack of coherence between the concepts applied and data observed and therefore a lack of understanding of the subject matter. Typical levels of heterogeneity thus offer a useful but neglected perspective on the levels of understanding achieved in psychological science. Focusing on continuous outcome variables, we surveyed heterogeneity in 150 meta-analyses from cognitive, organizational, and social psychology and 57 multiple close replications. Heterogeneity proved to be very high in meta-analyses, with powerful moderators being conspicuously absent. Population effects in the average meta-analysis vary from small to very large for reasons that are typically not understood. In contrast, heterogeneity was moderate in close replications. A newly identified relationship between heterogeneity and effect size allowed us to make predictions about expected heterogeneity levels. We discuss important implications for the formulation and evaluation of theories in psychology. On the basis of insights from the history and philosophy of science, we argue that the reduction of heterogeneity is important for progress in psychology and its practical applications, and we suggest changes to our collective research practice toward this end.

Structural biology is developing into a universal tool for visualizing biological processes in space and time at atomic resolution. The field has been built by established methodology like X-ray crystallography, electron microscopy and solution NMR and is now incorporating new techniques, such as small-angle X-ray scattering, electron tomography, magic-angle-spinning solid-state NMR and femtosecond X-ray protein nanocrystallography. These new techniques all seek to investigate non-crystalline, native-like biological material. Solid-state NMR is a relatively young technique that has just proven its capabilities for de novo structure determination of model proteins. Further developments promise great potential for investigations on functional biological systems such as membrane-integrated receptors and channels, and macromolecular complexes attached to cytoskeletal proteins. Here, we review the development and applications of solid-state NMR from the first proof-of-principle investigations to mature structure determination projects, including membrane proteins. We describe the development of the methodology by looking at examples in detail and provide an outlook towards future 'big' projects., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

With the technique of dynamic nuclear polarization (DNP) signal intensity in solid-state MAS-NMR experiments can be enhanced by 2-3 orders of magnitude. DNP relies on the transfer of electron spin polarization from unpaired electrons to nuclear spins. For this reason, stable organic biradicals such as TOTAPOL are commonly added to samples used in DNP experiments. We investigated the effects of biradical concentration on the relaxation, enhancement, and intensity of NMR signals, employing a series of samples with various TOTAPOL concentrations and uniformly (13)C, (15)N labeled proline. A considerable decrease of the NMR relaxation times (T(1), T(2)(∗), and T(1)(ρ)) is observed with increasing amounts of biradical due to paramagnetic relaxation enhancement (PRE). For nuclei in close proximity to the radical, decreasing T(1)(ρ) reduces cross-polarization efficiency and decreases in T(2)(∗) broaden the signal. Additionally, paramagnetic shifts of (1)H signals can cause further line broadening by impairing decoupling. On average, the combination of these paramagnetic effects (PE; relaxation enhancement, paramagnetic shifts) quenches NMR-signals from nuclei closer than 10Å to the biradical centers. On the other hand, shorter T(1) times allow the repetition rate of the experiment to be increased, which can partially compensate for intensity loss. Therefore, it is desirable to optimize the radical concentration to prevent additional line broadening and to maximize the signal-to-noise observed per unit time for the signals of interest., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Methods enabling structural studies of membrane-integrated receptor systems without the necessity of purification provide an attractive perspective in membrane protein structural and molecular biology. This has become feasible in principle since the advent of dynamic nuclear polarization (DNP) magic-angle-spinning NMR spectroscopy, which delivers the required sensitivity. In this pilot study, we observed well-resolved solid-state NMR spectra of extensively (13)C-labeled neurotoxin II bound to the nicotinic acetylcholine receptor (nAChR) in native membranes. We show that TOTAPOL, a biradical required for DNP, is localized at membrane and protein surfaces. The concentration of active, membrane-attached biradical decreases with time, probably because of reactive components of the membrane preparation. An optimal distribution of active biradical has strong effects on the NMR data. The presence of inactive TOTAPOL in membrane-proximal situations but active biradical in the surrounding water/glycerol "glass" leads to well-resolved spectra, yet a considerable enhancement (ε = 12) is observed. The resulting spectra of a protein ligand bound to its receptor are paving the way for further DNP investigations of proteins embedded in native membrane patches., (© 2011 American Chemical Society)

X-ray crystallography using synchrotron radiation and the technique of dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) require samples to be kept at temperatures below 100 K. Protein dynamics are poorly understood below the freezing point of water and down to liquid nitrogen temperatures. Therefore, we investigate the α-spectrin SH3 domain by magic angle spinning (MAS) solid state NMR (ssNMR) at various temperatures while cooling slowly. Cooling down to 95 K, the NMR-signals of SH3 first broaden and at lower temperatures they separate into several peaks. The coalescence temperature differs depending on the individual residue. The broadening is shown to be inhomogeneous by hole-burning experiments. The coalescence behavior of 26 resolved signals (of 62) was compared to water proximity and crystal structure Debye-Waller factors (B-factors). Close proximity to the solvent and large B-factors (i.e. mobility) lead, generally, to a higher coalescence temperature. We interpret a high coalescence temperature as indicative of a large number of magnetically inequivalent populations at cryogenic temperature., (© Springer Science+Business Media B.V. 2011)

A chemical system based on the dialysis principle was used to study protein loss of dental enamel during demineralization with an acetic-acid buffer solution containing calcium and phosphate, in which the fluoride-ion activity was kept constant. This resulted in a subsurface lesion, with a depth of about 130 microns. After demineralization, protein material was isolated from the demineralization solution. u.v. Spectra of the protein showed strong absorbance between 240 and 300 nm. Amino-acid composition showed high glycine, glutamic acid, proline, serine and aspartic acid contents. After 10 days demineralization, the total protein loss was 3 micrograms cm-2; the mineral loss was 16 mg cm-2. Compared with the total enamel-protein content (0.06-0.09 wt per cent) protein loss (0.018 per cent of total lost material) was not proportional to the mineral loss, when a subsurface lesion was formed.

This paper presents a new powerful method, longitudinal microradiography (LMR), with which it is possible to follow the mineral content in a de- or remineralizing carious tooth sample as a function of position on the surface of the mineralizing tissue independent of the sample thickness. Planoparallel tooth slices (thickness 300-400 microns) are cut parallel to the labial tooth surface and then fixed on a PMMA holder. Repeated microradiographic images of the same tissue slice together with an aluminium step wedge are made on photographic film at different times of mineralisation. The images are scanned under a densitometer with a microcomputer and the mineral content per unit tooth area at the same discrete tooth-slice surface positions is calculated (maximum predefined area is 5 mm x 5 mm, 15 x 15 positions). The change of mineral in one tooth slice per unit tooth surface area can be calculated at different times of mineralisation locally, as well as averaged over the total tooth-slice surface area. The SD in average mineral change is 0.009 kg m-2, which corresponds approximately to the mineral loss involved with a 8 microns deep tooth enamel carious lesion. All results are stored on disc. In an example, the enamel surfaces (6 mm2) of five human tooth enamel slices were exposed to an acetic acid buffer solution (pH 4.8) containing Ca, P and F. The mineral content variations in the enamel sample were followed in time by longitudinal microradiography. Mineral content evaluation shows in all cases a gradual increase in mineral loss. 3D plots of the mineral loss per unit area against tooth surface position at different stages of demineralisation of the same sample show an excellent uniform local behaviour in time with all tooth slices.

Both longitudinal microradiography (LMR) and scanning optical monitoring (OM) are non-destructive methods for measuring mineral changes in dental tooth enamel slices with time at 169 locations on the slice. Average calcium losses from four human tooth enamel slices (300-400 micron thickness), etched in HClO4, were determined by LMR and chemical analysis (C). As predicted from theory, LMR and C correlate very well (r = 0.99), but the appearance of a systematic error of unknown source of 30% made with LMR, C, or both could not be avoided. Another, more complex, experiment concerned six human tooth enamel slices of the same thickness which were demineralized in an aqueous buffered acid solution containing Ca and PO4. From this experiment it was found that average calcium loss as measured by C and LMR correlated well with the optical scattering as measured with scanning OM (Spearman rank correlation rs approximately equal to 0.79). It was also found that three-dimensional plots of local calcium loss by LMR and scanning OM as a function of tooth slice surface position show a well-defined tooth-dependent increase due to local demineralization and rather similar behaviour with time. From the experiments it follows that LMR and scanning OM are reliable methods to determine the mineral change in a tooth tissue as a function of local tooth slice surface position and of time and that with LMR and scanning OM time- and position-dependent measurements with an oral device become feasible.

The exposure of bovine enamel to an albumin-containing demineralizing solution results in penetration of protein into the porous enamel. Washing of this albumin-containing enamel results in a complete (low pretreatment albumin concentrations) or partial removal of the albumin (pretreatment concentrations greater than or equal to 200 micrograms/ml-1). Subsequent exposure to increasing salt concentrations of fluoride, phosphate, calcium or chloride shows a partial removal of albumin at fluoride or phosphate concentrations of 75 mM while complete removal occurred at 150-200 mM fluoride or phosphate. Exposure to either calcium or chloride, even at 3 M concentrations, showed a negligible albumin release. It is proposed that protein removed at high fluoride or phosphate concentrations is bound by a strong interaction between protein-carboxyl groups and calcium on the surface of the enamel mineral. The partial removal of albumin released at low fluoride or phosphate concentrations indicates an enamel-albumin interaction by means of Ca-bridging between protein-carboxyl groups and mineral phosphates. Finally, it is suggested that salt-free washing removes albumin that has lost its native form upon binding to the partially dissolved crystallites of the enamel. It is concluded that enamel is mainly protected from demineralization by the inhibitory effects of protein penetrated into the pores, in addition to possible protection by the pellicle on the surface.

Mineral distributions with and without a softened surface layer were studied. The molar Ca:P ratio of released material was due to preferential Ca-loss significantly higher from surface-softened enamel than from lesions. The molecular weight (less than 1800) distributions of released proteinaceous matter were similar. The protein release during surface softening contained more large peptides, whereas its amino-acid composition was more acidic amino acids compared with lesion formation. The protein content of released material during demineralization, acetic acid-soluble protein (at pH 4.5) and total protein of sound enamel showed that (i) enamel proteins were partially soluble in an acetic acid-buffer under mild acidic conditions and (ii) enamel proteins soluble in acetic acid-solution were partially released during demineralization. It is postulated that during enamel demineralization the dissolution of acid-soluble proteinaceous matter and its partial adsorption on newly-created sites of partially-dissolved crystals may explain the partial release of acid-soluble proteins. In case of lesion formation on the other hand new adsorption sites on new crystal surfaces formed in the surface layer are formed as well, which may account for the differences in mol.wt distribution and amino-acid composition.