Sub-structure formation in starless cores

Motivated by recent observational searches of sub-structure in starless molecular cloud cores, we investigate the evolution of density perturbations on scales smaller than the Jeans length embedded in contracting isothermal clouds, adopting the same formalism developed for the expanding Universe and the solar wind. We find that initially small amplitude, Jeans-stable perturbations (propagating as sound waves in the absence of a magnetic field), are amplified adiabatically during the contraction, approximately conserving the wave action density, until they either become nonlinear and steepen into shocks at a time $t_{\rm nl}$, or become gravitationally unstable when the Jeans length decreases below the scale of the perturbations at a time $t_{\rm gr}$. We evaluate analytically the time $t_{\rm nl}$ at which the perturbations enter the non-linear stage using a Burgers' equation approach, and we verify numerically that this time marks the beginning of the phase of rapid dissipation of the kinetic energy of the perturbations. We then show that for typical values of the rms Mach number in molecular cloud cores, $t_{\rm nl}$ is smaller than $t_{\rm gr}$, and therefore density perturbations likely dissipate before becoming gravitational unstable. Solenoidal modes grow at a faster rate than compressible modes, and may eventually promote fragmentation through the formation of vortical structures.Comment: 8 pages, 4 figure

Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(001)

The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level due to quantum size effects (QSE). QSE are expected to affect the film morphology and structure leading to the low temperature (LT) ``electronic growth'' of metals on semiconductors. In particular, layer-by-layer growth of Pb(111) films has been reported for deposition on Ge(001) below 130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer, pseudomorphic to the substrate, already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on Ge(001), where the apparent height of the Pb(111) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20 % have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied by inelastic HAS to measure the acoustic dispersion of the low energy phonons.Comment: 28 pages (laTex,elsart) and 13 figures (eps); updated reference

Study of the isotropic contribution to the analysis of photoelectron diffraction experiments at the ALOISA beamline

The angular distribution of the intensity in photoemission experiments is affected by electron diffraction patterns and by a smoothly varying ISO contribution originated by both intrumental details and physical properties of the samples. The origin of the various contributions to the ISO component has been identified since many years. Nonetheless in this work we present original developement of the ED analysis, which arises from the evolution of instrumental performance, in terms of analyzers positioning and angular resolution, as well as collimation and size of X-ray beams in third generation synchrotron sources. The analytical treatement of the instrumental factors is presented in detail for the end station of the ALOISA beamline (Trieste Synchrotron), where a wide variety of scattering geometries is available for ED experiments. We present here the basic formulae and their application to experimental data taken on the Fe/Cu3Au(001) system in order to highlight the role of the various parameters included in the distribution function. A specific model for the surface illumination has been developed as well as the overlayer thickness and surface roughness have been considered.Comment: RevTex, nine pages with five eps figures; to be published in J. Electron Spectrosc. Relat. Pheno

Do people with musculoskeletal pain differ from healthy cohorts in terms of global measures of strength? A systematic review and meta-analysis

Objective It is currently unknown if people with musculoskeletal pain display different multi-joint strength capacities than healthy cohorts. The aim was to investigate whether people with musculoskeletal pain show differences in global measures of strength in comparison to healthy cohorts. Data sources A systematic review was conducted using three databases (Medline, CINAHL and SPORTDiscus) and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Review methods Studies involving participants with painful musculoskeletal conditions and multi-joint strength assessment measured at baseline were included. A meta-analysis was also performed to compute standardized mean differences (± 95% confidence intervals), using Hedge’s g, and examined the differences in multi-joint strength at baseline between participants with painful musculoskeletal conditions and healthy participants. Results 5043 articles were identified, of which 20 articles met the inclusion criteria and were included in the qualitative analysis. The available evidence revealed that multi-joint strength values were limited to knee osteoarthritis, fibromyalgia, chronic low back pain, and rheumatoid arthritis. Only four studies were included in the quantitative synthesis and revealed that only small differences in both chest press (g= -0.34, 95% CI [-0.64, -0.03]) and leg press (g= -0.25, 95% CI [-0.49, -0.02]) existed between adult women with fibromyalgia and active community women. Conclusion There is a paucity of multi-joint strength values in participants with musculoskeletal pain. Quantitative comparison with healthy cohorts was limited, except for those with fibromyalgia. Adult women with fibromyalgia displayed reduced multi-joint strength values in comparison to active community women

Implications of no-tillage system in faba bean production: Energy analysis and potential agronomic benefits

Background: Given the nutritional value of faba bean, however its susceptibility to water deficit, especially in Mediterranean environment, tillage practices need to be modified in order to adapt the crop to dry and low rainfall conditions and promote the interest in its cultivation. Objective: To identify whether no-tillage system can be considered as a sustainable means in faba bean cultivation under Mediterranean condition. Method: The study was conducted during a 6-year period (2010/11 to 2015/16) in southern Italy within wheat-faba bean rotation framework of a long-term experiment. The effect of No-Tillage (NT) on agronomic and energy parameters of faba bean (Vicia faba L.) cultivation was evaluated and compared to those of Conventional (CT) and Reduced (RT) Tillage. Results: The agronomic results indicate that NT performed better and/or is comparable to CT, while its application was 28% and 30% more energy efficient compared to CT and RT respectively. For agronomic parameters, tillage had a significant effect on number of plant m -2 , grain yield, grain protein content and 100-seed weight whereas year effect was significant for yield components and quality parameters. Energy indexes, instead, were significantly affected by both factors. NT gave the best results in terms of energy efficiency, energy intensity and net energy, and consumed 39% and 36% less non-renewable energy than CT and RT, respectively. Conclusion: Our findings revealed that the key benefit of NT in rainfed faba bean is its ability to produce sufficient yield of high quality with a significant reduction in energy inputs entailed the fewest field operations and therefore lowest energy requirements

Oregano and its potential use as bioherbicide

Widespread use of synthetic herbicides in weed control could result in negative impact on human health and on the environment. Natural compounds could be successfully used as bioherbicides because they are potentially more environmental friendly and safe. Plants are an important source of active compounds. In particular, many species belonging to the Labiate family produce essential oils containing compounds that could act as natural herbicides. In this paper we report on preliminary studies about the effects on seed germination and plant growth of an oregano hybrid (Origanum vulgare L. ssp. virilidum × O. vulgare L. ssp. hirtum (Link) Iestwart). Experiments were done both in pots and in the field. Increasing amounts of chopped leaves and stems of oregano were added to the soil. In the pots, several weed species were sown, whereas naturally occurring infestation was evaluated in the field. In comparison with the control, a reduced number of weeds was observed where oregano biomass was added. The above-mentioned trend was more visible in the pots than in the field. The results suggest that the hybrid of oregano used in the trial could be an interesting source of natural compounds effective against weeds. Hence, further studies with this plant are likely to be successful

Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind

The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma is investigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and vanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuations exhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to an overall anisotropic proton heating, protons are heated in the perpendicular direction, and, initially, also in the parallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropy which is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome the expansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a form of localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This work demonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime

Scale dependence and cross-scale transfer of kinetic energy in compressible hydrodynamic turbulence at moderate Reynolds numbers

We investigate properties of the scale dependence and cross-scale transfer of kinetic energy in compressible three-dimensional hydrodynamic turbulence, by means of two direct numerical simulations of decaying turbulence with initial Mach numbers M = 1/3 and M = 1, and with moderate Reynolds numbers, R_lambda ~ 100. The turbulent dynamics is analyzed using compressible and incompressible versions of the dynamic spectral transfer (ST) and the Karman-Howarth-Monin (KHM) equations. We find that the nonlinear coupling leads to a flux of the kinetic energy to small scales where it is dissipated; at the same time, the reversible pressure-dilatation mechanism causes oscillatory exchanges between the kinetic and internal energies with an average zero net energy transfer. While the incompressible KHM and ST equations are not generally valid in the simulations, their compressible counterparts are well satisfied and describe, in a quantitatively similar way, the decay of the kinetic energy on large scales, the cross-scale energy transfer/cascade, the pressure dilatation, and the dissipation. There exists a simple relationship between the KHM and ST results through the inverse proportionality between the wave vector k and the spatial separation length l as k l ~ 3^1/2. For a given time the dissipation and pressure-dilatation terms are strong on large scales in the KHM approach whereas the ST terms become dominant on small scales; this is owing to the complementary cumulative behavior of the two methods. The effect of pressure dilatation is weak when averaged over a period of its oscillations and may lead to a transfer of the kinetic energy from large to small scales without a net exchange between the kinetic and internal energies. Our results suggest that for large-enough systems there exists an inertial range for the kinetic energy cascade ...Comment: 14 pages, 10 figure