Hasil untuk "physics.atom-ph"

Wenchao Sheng, Z. Zhuang, Minrui Gao et al.

The hydrogen oxidation/evolution reactions are two of the most fundamental reactions in distributed renewable electrochemical energy conversion and storage systems. The identification of the reaction descriptor is therefore of critical importance for the rational catalyst design and development. Here we report the correlation between hydrogen oxidation/evolution activity and experimentally measured hydrogen binding energy for polycrystalline platinum examined in several buffer solutions in a wide range of electrolyte pH from 0 to 13. The hydrogen oxidation/evolution activity obtained using the rotating disk electrode method is found to decrease with the pH, while the hydrogen binding energy, obtained from cyclic voltammograms, linearly increases with the pH. Correlating the hydrogen oxidation/evolution activity to the hydrogen binding energy renders a monotonic decreasing hydrogen oxidation/evolution activity with the hydrogen binding energy, strongly supporting the hypothesis that hydrogen binding energy is the sole reaction descriptor for the hydrogen oxidation/evolution activity on monometallic platinum. Hydrogen oxidation and evolution are two of the key reactions in renewable energy conversion and storage devices. Here, the authors report the correlation between reaction rate and measured hydrogen binding energy for polycrystalline platinum in buffer solutions ranging from pH 0 to 13.

C. Lauber, M. Hamady, R. Knight et al.

Hong-Jun Li, Jin-Zhi Du, Jing Liu et al.

Boeun Lee, Hyoree Seo, Hae Ri Lee et al.

L. Giordano, B. Han, M. Risch et al.

E. A. Miller, D. Beasley, R. Dunn et al.

The human vaginal microbiome is dominated by bacteria from the genus Lactobacillus, which create an acidic environment thought to protect women against sexually transmitted pathogens and opportunistic infections. Strikingly, lactobacilli dominance appears to be unique to humans; while the relative abundance of lactobacilli in the human vagina is typically >70%, in other mammals lactobacilli rarely comprise more than 1% of vaginal microbiota. Several hypotheses have been proposed to explain humans' unique vaginal microbiota, including humans' distinct reproductive physiology, high risk of STDs, and high risk of microbial complications linked to pregnancy and birth. Here, we test these hypotheses using comparative data on vaginal pH and the relative abundance of lactobacilli in 26 mammalian species and 50 studies (N = 21 mammals for pH and 14 mammals for lactobacilli relative abundance). We found that non-human mammals, like humans, exhibit the lowest vaginal pH during the period of highest estrogen. However, the vaginal pH of non-human mammals is never as low as is typical for humans (median vaginal pH in humans = 4.5; range of pH across all 21 non-human mammals = 5.4–7.8). Contrary to disease and obstetric risk hypotheses, we found no significant relationship between vaginal pH or lactobacilli relative abundance and multiple metrics of STD or birth injury risk (P-values ranged from 0.13 to 0.99). Given the lack of evidence for these hypotheses, we discuss two alternative explanations: the common function hypothesis and a novel hypothesis related to the diet of agricultural humans. Specifically, with regard to diet we propose that high levels of starch in human diets have led to increased levels of glycogen in the vaginal tract, which, in turn, promotes the proliferation of lactobacilli. If true, human diet may have paved the way for a novel, protective microbiome in human vaginal tracts. Overall, our results highlight the need for continuing research on non-human vaginal microbial communities and the importance of investigating both the physiological mechanisms and the broad evolutionary processes underlying human lactobacilli dominance.

Yirui Cheng, Qingyu Zeng, Qing Han et al.

Exosomes are cup-shaped small (30–150 nm) extracellular vesicles with the structure of lipid bilayer membrane (Tkach and Thery, 2016) containing proteins, mRNAs and microRNAs that mediate intercellular communication (Valadi et al., 2007). Unlike other extracellular vesicles, exosomes are released into the extracellular space when the multivesicular bodies (MVBs) fuse with the plasma membrane (Colombo et al., 2014). Almost all cell types can secret exosomes and exosomes exist in diverse biological fluids, such as blood, urine, saliva, hydrothorax and breast milk (Thery et al., 2006). Up to now, a number of studies have demonstrated the functions of exosomes in disease development and the potential clinical applications in diagnosis and therapy (Shao et al., 2016). To conduct reproducible studies on exosomal content and function, storage conditions need to have minimal impact on exosomes. There have been a few studies providing partial confirmation of the effect of different storage conditions on exosomes currently. Using exosomes from urine (Zhou et al., 2006) and conditioned medium (Lee et al., 2016) respectively to investigate the influence of storage temperature on exosomes as measured by Western blot, both groups have concluded that storage below −70 °C for a long time is the best temperature for the recovery of exosomes. On the other hand, Sokolova et al. (2011) applied nanoparticle tracking analysis (NTA) to measure the size changes of exosomes at different temperatures, revealing that storage at 37 °C led to more reduction in exosome sizes than that at 4 °C. However, in this study no information about changes in the particle concentration was reported. Some other studies revealed the effect of pH, storage temperature and cycles of freezing and thawing only on the yield of exosome isolation, but not on quantity changes during storage (Akers et al., 2016; Ban et al., 2015; Zhao et al., 2017). Therefore, the standard criterion of exosomal preservation condition is still undefined. Herein, we used HEK 293T cells and ExtraPEG method (Rider et al., 2016) to investigate the influence of multiple storage conditions (temperature, cycles of freezing and thawing, pH) on the quantity changes and cellular uptake of exosomes. ExtraPEG is a new polyethylene glycol (PEG) precipitation method for the purification exosomes without affecting their biological activity. Generally, ultracentrifugation (UC) (Mincheva-Nilsson et al., 2016) is most reliable but time-consuming; and precipitation methods such as ExoQuick (patent number: US20130337440 A1) and ExtraPEG can obtain higher yields of exosomes but with impurity of coprecipitated proteins. First, exosomes from the conditioned medium were extracted by ExtraPEG or UC method. After isolation, transmission electron microscope (TEM), NTA and Western blot were performed to analyze exosomes. Exosomes extracted by UC or ExtraPEG were similar in cupshaped structure (Fig. S1A and S1B), size distribution (Fig. S1C and S1D). And as representative exosome biomarkers, ALG-2-interacting protein X (ALIX), heat shock protein 70 (HSP70) and tumor susceptibility gene 101 (TSG101) were detected in exosomal protein while β-tubulin, widely used as an internal reference to analyze intracellular protein levels, was not detected in exosome samples (Fig. S1E and S1F). These data indicated exosomes were successfully isolated by ExtraPEG method and suitable for the following experiments. After isolation, the exosome pellets were divided equally into several portions and each portion was stored at different temperatures (−80 °C, −20 °C, 4 °C, 37 °C and 60 °C), or through 1–5 cycles of freezing to −80 °C and thawing, or at different pH levels (pH 4, pH 7 and pH 10). After 24 h, NTA and Western blot were performed to measure the remaining quantity of exosomes. Regarding temperatures, the exosomes stored at 4 °C had the highest concentration (Fig. 1A). Consistent with the NTA results, the exosomes stored at 4 °C showed higher levels of representative exosome markers ALIX, HSP70 and TSG101 (Fig. 1B). With the increasing cycles of freezing and thawing, the exosomal concentration and protein levels of ALIX, HSP70 and TSG101 all decreased (Fig. 1D and 1E). For different pH levels, the loss of exosomal concentration and three exosome markers ALIX, HSP70 and TSG101 at pH 4 and pH 10 was more than that at pH 7 (Fig. 1E and 1F). Interestingly, exosomes stored at pH 4 decreased more sharply than that at pH 10 (Fig. 1F and 1G), suggesting that acidic

Xiaorong Fan, Zhong Tang, Yawen Tan et al.

A. Abuhelwa, Desmond B. Williams, R. Upton et al.

Salime Bazban-Shotorbani, M. M. Hasani-Sadrabadi, A. Karkhaneh et al.

S. Nakata, Mao Shiomi, Yusuke Fujita et al.

Sandeep J. Sonawane, Rahul S. Kalhapure, T. Govender

Sonda Benelhadj, Adem Gharsallaoui, P. Degraeve et al.

Pedro Sancho

We analyze the electronic correlation contribution to the time delay in the photo-ionization of the excited ortho- and para-Helium states. A simple estimation, based on the ionization probability amplitudes, shows that the different form of anti-symmetrising both states can in principle lead to very different values of the correlation time delay. This result illuminates the interplay between electronic correlations and symmetrisation effects in the attosecond regime, a relation that has been studied in other contexts. Moreover, it suggests the potential of excited states to explore the role of exchange effects in that realm.

Ruijie Du

We derive solutions of the Schrödinger equation for the isotropic van der Waals interaction in a symmetric harmonic trap, with the recent approach [arXiv:2207.09377 (2022)] to handle the multi-scale long-range potential. Asymptotic behaviors of these solutions are then obtained for $r\rightarrow 0$ and $r\rightarrow \infty$. We further deduce the energy spectrum of the two-body relative motion and relate the spectrum to scattering lengths for $s$ wave and $p$ wave. These results can be used to research trapped atom-atom collisions and energy spectra.

Krzysztof Pachucki

A general quantum electrodynamic method for derivation of nuclear recoil corrections in hydrogenic systems, which are exact in the nuclear charge parameter $Z\,α$, is introduced. The exemplary derivation is presented for the $O(m/M)$ nuclear pure recoil correction to the hyperfine splitting. The obtained result is verified by comparison to the known $(Z\,α)^5$ contribution

N. Barrow

M. Kosmulski

B. Cerozi, K. Fitzsimmons

Yuting Zhang, Hong Shen, Xinhua He et al.

Application of chemical fertilizer or manure can affect soil microorganisms directly by supplying nutrients and indirectly by altering soil pH. However, it remains uncertain which effect mostly shapes microbial community structure. We determined soil bacterial diversity and community structure by 454 pyrosequencing the V1-V3 regions of 16S rRNA genes after 7-years (2007–2014) of applying chemical nitrogen, phosphorus and potassium (NPK) fertilizers, composted manure or their combination to acidic (pH 5.8), near-neutral (pH 6.8) or alkaline (pH 8.4) Eutric Regosol soil in a maize-vegetable rotation in southwest China. In alkaline soil, nutrient sources did not affect bacterial Operational Taxonomic Unit (OTU) richness or Shannon diversity index, despite higher available N, P, K, and soil organic carbon in fertilized than in unfertilized soil. In contrast, bacterial OTU richness and Shannon diversity index were significantly lower in acidic and near-neutral soils under NPK than under manure or their combination, which corresponded with changes in soil pH. Permutational multivariate analysis of variance showed that bacterial community structure was significantly affected across these three soils, but the PCoA ordination patterns indicated the effect was less distinct among nutrient sources in alkaline than in acidic and near-neural soils. Distance-based redundancy analysis showed that bacterial community structures were significantly altered by soil pH in acidic and near-neutral soils, but not by any soil chemical properties in alkaline soil. The relative abundance (%) of most bacterial phyla was higher in near-neutral than in acidic or alkaline soils. The most dominant phyla were Proteobacteria (24.6%), Actinobacteria (19.7%), Chloroflexi (15.3%) and Acidobacteria (12.6%); the medium dominant phyla were Bacterioidetes (5.3%), Planctomycetes (4.8%), Gemmatimonadetes (4.5%), Firmicutes (3.4%), Cyanobacteria (2.1%), Nitrospirae (1.8%), and candidate division TM7 (1.0%); the least abundant phyla were Verrucomicrobia (0.7%), Armatimonadetes (0.6%), candidate division WS3 (0.4%) and Fibrobacteres (0.3%). In addition, Cyanobacteria and candidate division TM7 were more abundant in acidic soil, whereas Gemmatimonadetes, Nitrospirae and candidate division WS3 were more abundant in alkaline soil. We conclude that after 7-years of fertilization, soil bacterial diversity and community structure were shaped more by changes in soil pH rather than the direct effect of nutrient addition.