Nanoclay-Directed Structure and Morphology in PVDF Electrospun Membranes

The incorporation of organically modified Lucentite nanoclay dramatically modifies the structure and morphology of the PVDF electrospun fibers. In a molecular level, the nanoclay preferentially stabilizes the all-trans conformation of the polymer chain, promoting an α to β transformation of the crystalline phase. The piezoelectric properties of the β-phase carry great promise for energy harvest applications. At a larger scale, the nanoclay facilitates the formation of highly uniform, bead-free fibers. Such an effect can be attributed to the enhanced conductivity and viscoelasticity of the PVDF-clay suspension. The homogenous distribution of the directionally aligned nanoclays imparts advanced mechanical properties to the nanofibers

UV Upturn in Elliptical Galaxies: Theory

The UV upturn is the rising flux with decreasing wavelength between the Lyman limit and 2500\AA found virtually in all bright spheroidal galaxies. It has been a mystery ever since it was first detected by the OAO-2 space telescope (Code & Welch 1979) because such old metal-rich populations were not expected to contain any substantial number of hot stars. It was confirmed by following space missions, ANS (de Boer 1982), IUE (Bertola et al. 1982) and HUT (Brown et al. 1997). The positive correlation between the UV-to-optical colour (i.e., the strength of the UV upturn) and the Mg2 line strength found by Burstein et al. (1987) through IUE observations has urged theorists to construct novel scenarios in which metal-rich ($\gtrsim Z_{\odot}$) old ($\gtrsim$ a few Gyr) stars become UV bright (Greggio & Renzini 1990; Horch et al. 1992). Also interesting was to find using HUT that, regardless of the UV strength, the UV spectral slopes at 1000--2000\AA in the six UV bright galaxies were nearly identical suggesting a very small range of temperatures of the UV sources in these galaxies (Brown et al. 1997), which corresponds to $T_{\rm eff} \approx 20,000 \pm 3,000$ K. This, together with other evidence, effectively ruled out young stars as the main driver of the UV upturn. A good review on the observational side of the story is given in the next article by Tom Brown, as well as in the recent articles of Greggio & Renzini (1999) and O'Connell (1999).Comment: 6 figures; belated paper from Keele Conferenc

Estimation of COVID-19 spread curves integrating global data and borrowing information

Currently, novel coronavirus disease 2019 (COVID-19) is a big threat to global health. The rapid spread of the virus has created pandemic, and countries all over the world are struggling with a surge in COVID-19 infected cases. There are no drugs or other therapeutics approved by the US Food and Drug Administration to prevent or treat COVID-19: information on the disease is very limited and scattered even if it exists. This motivates the use of data integration, combining data from diverse sources and eliciting useful information with a unified view of them. In this paper, we propose a Bayesian hierarchical model that integrates global data for real-time prediction of infection trajectory for multiple countries. Because the proposed model takes advantage of borrowing information across multiple countries, it outperforms an existing individual country-based model. As fully Bayesian way has been adopted, the model provides a powerful predictive tool endowed with uncertainty quantification. Additionally, a joint variable selection technique has been integrated into the proposed modeling scheme, which aimed to identify possible country-level risk factors for severe disease due to COVID-19

Fatigability and Recovery of Arm Muscles with Advanced Age for Dynamic and Isometric Contractions

This study determined whether age-related mechanisms can increase fatigue of arm muscles during maximal velocity dynamic contractions, as it occurs in the lower limb. We compared elbow flexor fatigue of young (n = 10, 20.8 ± 2.7 years) and old men (n = 16, 73.8 ± 6.1 years) during and in recovery from a dynamic and an isometric postural fatiguing task. Each task was maintained until failure while supporting a load equivalent to 20% of maximal voluntary isometric contraction (MVIC) torque. Transcranial magnetic stimulation (TMS) was used to assess supraspinal fatigue (superimposed twitch, SIT) and muscle relaxation. Time to failure was longer for the old men than for the young men for the isometric task (9.5 ± 3.1 vs. 17.2 ± 7.0 min, P = 0.01) but similar for the dynamic task (6.3 ± 2.4 min vs. 6.0 ± 2.0 min, P = 0.73). Initial peak rate of relaxation was slower for the old men than for the young men, and was associated with a longer time to failure for both tasks (P \u3c 0.05). Low initial power during elbow flexion was associated with the greatest difference (reduction) in time to failure between the isometric task and the dynamic task (r = − 0.54, P = 0.015). SIT declined after both fatigue tasks similarly with age, although the recovery of SIT was associated with MVIC recovery for the old (both sessions) but not for the young men. Biceps brachii and brachioradialis EMG activity (% MVIC) of the old men were greater than that of the young men during the dynamic fatiguing task (P \u3c 0.05), but were similar during the isometric task. Muscular mechanisms and greater relative muscle activity (EMG activity) explain the greater fatigue during the dynamic task for the old men compared with the young men in the elbow flexor muscles. Recovery of MVC torque however relies more on the recovery of supraspinal fatigue among the old men than among the young men

Fermion Production in Strong Magnetic Field and its Astrophysical Implications

We calculate the effective potential of a strong magnetic field induced by fermions with anomalous magnetic moments which couple to the electromagnetic field in the form of the Pauli interaction. For a uniform magnetic field, we find the explicit form of the effective potential. It is found that the non-vanishing imaginary part develops for a magnetic field stronger than a critical field and has a quartic form which is quite different from the exponential form of the Schwinger process. We also consider a linear magnetic field configuration as an example of inhomogeneous magnetic fields. We find that the imaginary part of the effective potential is nonzero even below the critical field and shows an exponentially decreasing behavior with respect to the inverse of the magnetic field gradient, which is the non-perturbative characteristics analogous to the Schwinger process. These results imply the instability of the strong magnetic field to produce fermion pairs as a purely magnetic effect. The possible applications to the astrophysical phenomena with strong magnetic field are also discussed.Comment: 13 pages, 3 figure

N_pN_n dependence of empirical formula for the lowest excitation energy of the 2^+ states in even-even nuclei

We examine the effects of the additional term of the type $\sim e^{- \lambda' N_pN_n}$ on the recently proposed empirical formula for the lowest excitation energy of the $2^+$ states in even-even nuclei. This study is motivated by the fact that this term carries the favorable dependence of the valence nucleon numbers dictated by the $N_pN_n$ scheme. We show explicitly that there is not any improvement in reproducing $E_x(2_1^+)$ by including the extra $N_pN_n$ term. However, our study also reveals that the excitation energies $E_x(2_1^+)$, when calculated by the $N_pN_n$ term alone (with the mass number $A$ dependent term), are quite comparable to those calculated by the original empirical formula.Comment: 14 pages, 5 figure