A twist in chiral interaction between biological helices

Using an exact solution for the pair interaction potential, we show that long, rigid, chiral molecules with helical surface charge patterns have a preferential interaxial angle ~((RH)^1/2)/L, where L is the length of the molecules, R is the closest distance between their axes, and H is the helical pitch. Estimates based on this formula suggest a solution for the puzzle of small interaxial angles in a-helix bundles and in cholesteric phases of DNA.Comment: 7 pages, 2 figures, PDF file onl

BMC Geriatr

Background Physical activity may decrease the risk of dementia; however, previous cohort studies seldom investigated the different types of physical activity and household activities. Our objective was to analyze the links between two physical activity types and dementia in older people. Methods The study used data from the prospective observational Three-city cohort and included 1550 community-dwelling individuals aged 72 to 87 without dementia at baseline. Physical activity was assessed with the Voorrips questionnaire. Two sub-scores were calculated to assess household/transportation activities and leisure/sport activities. Restricted cubic spline and proportional hazard Cox models were used to estimate the non-linear exposure-response curve for the dementia risk and the appropriate activity level thresholds. Models were adjusted for possible confounders, including socio-demographic variables, comorbidities, depressive symptoms and APOE genotype. Results The median age was 80 years, and 63.6% of participants were women. After a median follow-up of 4.6 years, dementia was diagnosed in 117 participants (7.6%). An inverse J-shaped association was found between household/transportation physical activity sub-score and dementia risk, which means that the risk is lowest for the moderately high values and then re-increases slightly for the highest values. The results remained significant when this sub-score was categorized in three classes (low, moderate, and high), with hazard ratios (95% confidence interval) of 0.55 (0.35–0.87) and 0.62 (0.38–1.01) for moderate and high activity levels, respectively. No significant effect was found for leisure/sport activities. Conclusions The 5-year risk of dementia was significantly and negatively associated with the household/transportation activity level, but not with the leisure and sport activity sub-score. This highlights the importance of considering all physical activity types in 72 years or older people

Comment on the narrow structure reported by Amaryan et al

The CLAS Collaboration provides a comment on the physics interpretation of the results presented in a paper published by M. Amaryan et al. regarding the possible observation of a narrow structure in the mass spectrum of a photoproduction experiment.Comment: to be published in Physical Review

Absorption of the ω\omega and ϕ\phi Mesons in Nuclei

Due to their long lifetimes, the $\omega$ and $\phi$ mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from $^{2}$H, C, Ti, Fe, and Pb targets. This paper reports the first measurement of the ratio of nuclear transparencies for the $e^{+}e^{-}$ channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels.Comment: 6 pages, 4 figure

Some Directions for Performance Improvement of Li-Ion Batteries out of Usual Paths

Recent developments at IMN will be shared on several research directions out of usual paths for performance improvement of Li-ion batteries. We will focus on innovative surface modifications of electrode components, new electrode compositions and architectures, and failure mechanism upon cycling by in-depth characterization through coupled advanced spectroscopic techniques. A molecular grafting approach has been proposed as a way to modify the interfacial chemical reactivity of oxide materials, which is detrimental to their long-term energy storage properties as electrodes of Li-ion batteries. Surface derivatization of powder oxide materials such as Li1.2V3O8 and Li(Mn,Ni)2O4 was accomplished by in situ electrografting of a diazonium salt during Li-ion intercalation, leading to a covalently bonded organic multilayer. Charge transfer is not impeded, while electrolyte decomposition is inhibited thus increasing the cycle life and decreasing the self-discharge. Carbon additives of classical porous electrodes occupy a large volume fraction which is lost for charge storage. Redox functionalization of the surface of some carbon additives has been successfully achieved through non-covalent grafting chemistry using multi-redox pyrene molecules synthesized on purpose. Such functionalized carbon additives have been used to increase the stored energy and power of C-coated LFP porous electrodes. Thicker electrodes are needed for higher energy density Li-ion batteries. We evaluate different directions in order to design new innovative electrode architectures for such a purpose. Our grafting chemistry has been further developed to achieve molecular junctions between non-carbon-coated LFP and multiwall carbon nanotubes (MWCNT) using a designed thiophene-based conjugated molecule. The strategy enables original architecturing of the cathode of Li-ion batteries, with the individual MWCNT being electronically nanocontacted at the surface of LFP grains. This advancement leads to much higher specific capacity and better capacity retention for non calendared thick electrodes, for which the electronic wiring of the electroactive material grains is a critical issue. Another direction followed is the use of conducting polymer additives in porous electrodes, which are able to act as both conducting fillers and mechanical reinforcement materials. We have synthesized a new form of lithium doped PANI, the excellent properties of which in terms of specific capacity, stability on cycling and rate capability will be presented. The coating of bare LFP particles with thin layers of this new Li-doped PANI allows surpassing the performance of commercial carbon coated LFP thick electrodes. The role of this PANI additive into millimetric thick electrodes of NMC material will also be discussed. Future developments of higher energy density Si-based Li-ion batteries depend on the mastering of side reactions at the Si anode. We will compare the SEI composition and morphology at the Si surface upon cycling in half cell and full Li-ion cell configurations using a combination of 7Li, 19F MAS NMR, XPS, TOF-SIMS and STEM-EELS. The origin of the much faster aging of Si-based full cells versus half cells and future directions for improvement will be discusse

Near-threshold Photoproduction of Phi Mesons from Deuterium

We report the first measurement of the differential cross section on $\phi$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections $\frac{d\sigma}{dt}$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. This experiment establishes a baseline for a future experimental search for an exotic $\phi$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $\phi$ mesons

Transverse Polarization of Σ+(1189)\Sigma^{+}(1189) in Photoproduction on a Hydrogen Target in CLAS

Experimental results on the $\Sigma^+(1189)$ hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson laboratory are presented. The $\Sigma^+(1189)$ was reconstructed in the exclusive reaction $\gamma+p\rightarrow K^{0}_{S} + \Sigma^+(1189)$ via the $\Sigma^{+} \to p \pi^{0}$ decay mode. The $K^{0}_S$ was reconstructed in the invariant mass of two oppositely charged pions with the $\pi^0$ identified in the missing mass of the detected $p\pi^+\pi^-$ final state. Experimental data were collected in the photon energy range $E_{\gamma}$ = 1.0-3.5 GeV ($\sqrt{s}$ range 1.66-2.73 GeV). We observe a large negative polarization of up to 95%. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances.Comment: pages 1