We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO 2 . The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higherdensity crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal. DOI: 10.1103/PhysRevLett.112.025502 PACS numbers: 63.20.-e, 07.85.-m, 76.80.+y The low-temperature thermodynamic properties of glasses are accepted to be anomalously different from those of crystals due to the inherent disorder of the glass structure. At temperatures of ∼10 K, the specific heat of glasses shows an excess relativetothatofthecorrespondingcrystals.Theexcessspecific heat is related to a distinct feature in the spectrum of the atomic vibrations: At frequencies of ∼1 THz, glasses exhibit an excess of states above the Debye level of the acoustic waves, the socalled "boson peak." The excess of specific heat and the boson peak are universally observed for all glasses and by all relevant experimental techniques. However, the results still do not converge to a unified answer to how disorder causes these anomalies.Themajorityofthemodelsexplainthebosonpeakbyappealing tovarious glass-specific features. Theseincludelow-energy optical modes [1], onset of mechanical instability related to saddle points in the energy landscape [2] or to jamming [3][4][5], local vibrationalmodes of clusters [6] or locally favoured structures [7], librations [8] or other coherent motions [9] of molecular fragments, crossover of local and acoustic modes [10], quasilocal vibrations of atoms in an anharmonic potential [11], broadening of vibrational states in the Ioffe-Regel crossover regime [12], spatial variation of the elastic moduli [13], breakdown of the continuum approximation [14,15], and topologically diverse defects [16], to cite the most important ones.Alternatively, the boson peak is identified as the counterpart of the acoustic van Hove singularities of crystals, i.e., explained by the piling up of the vibrational states of the acousticlike branches near the boundary of the pseudoBrillouin zone [17][18][19][20].Diverging in explanations of the boson peak, all models agree that the excess states and the excess specific heat of

No abstract

We investigated molecular motions in the 0.3-350 ps time range of D2O-hydrated bilayers of 1-palmitoyl-oleoyl-sn-glycero-phosphocholine and 1,2-dimyristoyl-sn-glycero-phosphocholine in the liquid phase by quasielastic neutron scattering. Model analysis of sets of spectra covering scale lengths from 4.8 to 30 Å revealed the presence of three types of motion taking place on well-separated time scales: (i) slow diffusion of the whole phospholipid molecules in a confined cylindrical region; (ii) conformational motion of the phospholipid chains; and (iii) fast uniaxial rotation of the hydrogen atoms around their carbon atoms. Based on theoretical models for the hydrogen dynamics in phospholipids, the spatial extent of these motions was analysed in detail and the results were compared with existing literature data. The complex dynamics of protons was described in terms of elemental dynamical processes involving different parts of the phospholipid chain on whose motions the hydrogen atoms ride.

Background & Aims: There is a growing interest for the use of probiotics for chronic constipation. A recent randomized controlled trial (RCT) showed a positive effect of Lactobacillus reuteri (L. reuteri) on bowel movement frequency in infants with chronic constipation. The aim of the present study was to evaluate the effects of L. reuteri in adult patients with functional constipation.Methods: A double-blind, placebo RCT was conducted in 40 adults (18M/22F, 35±15 years) affected by functional constipation according to the Rome III criteria. Patients were randomly assigned to receive a supplementation of L. reuteri (DSM 17938), or matching placebo for 4 weeks. The increase of bowel movements/week was the primary outcome, while the improvement of stool consistency was the secondary outcome.Results: At week 4, the mean increase in bowel movements/week was 2.6 (SD±1.14, 95% CI:1.6-3.6) in the L. reuteri group and 1.0 (SD±1. 95% CI:0.12-1.88) in the placebo group (p=0.046). At the end of the treatment, the mean bowel movements/week was 5.28±1.93 in the L. reuteri group and 3.89±1.79 in the placebo group. There was a not significant difference in the stool consistency between the two groups.Conclusions: L. reuteri is more effective than the placebo in improving bowel movement frequency in adult patients with functional constipation as previously demonstrated in children, even if it seems to have no effect on stool consistency.

No abstract

Many polymers exhibit much steeper temperature dependence of their structural relaxation time (higher fragility) than liquids of small molecules, and the mechanism of this unusually high fragility in polymers remains a puzzle. To reveal additional hints for understanding the underlying mechanism, we analyzed correlation of many properties of polymers to their fragility on example of model polymer polystyrene with various molecular weights (MWs). We demonstrate that these correlations work for short chains (oligomers), but fail progressively with increase in MW. Our surprising discovery is that the steepness of the temperature dependence (fragility) of the viscosity that is determined by chain relaxation follows the correlations at all molecular weights. These results suggest that the molecular level relaxation still follows the behavior usual for small molecules even in polymers, and its fragility (chain fragility) falls in the range usual for molecular liquids. It is the segmental relaxation that has this unusually high fragility. We speculate that many polymers cannot reach an ergodic state on the time scale of segmental dynamics due to chain connectivity and rigidity. This leads to sharper decrease in accessible configurational entropy upon cooling and results in steeper temperature dependence of segmental relaxation. The proposed scenario provides a new important insight into the specifics of polymer dynamics: the role of ergodicity time and length scale. At the end, we suggest that a similar scenario can be applicable also to other molecular systems with slow intra-molecular degrees of freedom and to chemically complex systems where the time scale of chemical fluctuations can be longer than the time scale of structural relaxation.

Picosecond time scale dynamics of hydrated proteins has been connected with the onset of biological activity as it coincides with solvent-solute hydrogen bond rearrangements and amino acid rotational relaxation time scales. The presence and fluctuations of protein hydration water (PHW) largely influence protein motions that are believed to be slaved to those of the solvent, yet to date, how protein and hydration water dynamics are coupled remains unclear. Here, we provide a significant advance in characterizing this coupling; we present the first full study of both the longitudinal and transverse coherent collective motions in a protein-solvent system. The data show unexpectedly the presence in the water dynamics of collective modes belonging to the protein. The properties of these modes, in particular, their propagation velocities and amplitudes, indicate a strengthening of the interactions and a higher rigidity of the network of solvent molecules close to the protein surface. Accordingly, the present study presents the most compelling and clear evidence of a very strong dynamical coupling between a protein and its hydration water, previously suggested by studies using various experimental techniques.

Solar cells (SCs) are the most ubiquitous and reliable energy generation systems for aerospace applications. Nowadays, III–V multijunction solar cells (MJSCs) represent the standard commercial technology for powering spacecraft, thanks to their high‐power conversion efficiency and certified reliability/stability while operating in orbit. Nevertheless, spacecraft companies are still using cheaper Si‐based SCs to amortize the launching costs of satellites. Moreover, in recent years, new SCs technologies based on Cu(In,Ga)Se2 (CIGS) and perovskite solar cells (PSCs) have emerged as promising candidates for aerospace power systems, because of their appealing properties such as lightweightness, flexibility, cost‐effective manufacturing, and exceptional radiation resistance. In this review the current advancements and future challenges of SCs for aerospace applications are critically discussed. In particular, for each type of SC, a description of the device's architecture, a summary of its performance, and a quantitative assessment of the radiation resistance are presented. Finally, considering the high potential that 2D‐materials (such as graphene, transition metal dichalcogenides, and transition metal carbides, nitrides, and carbonitrides) have in improving both performance and stability of SCs, a brief overview of some important results concerning the influence of radiation on both 2D materials‐based devices and monolayer of 2D materials is also included.