Letteratura scientifica selezionata sul tema "Centre-of-mass energy spread"

In this study, a CFD analysis to evaluate effect of combustion chamber geometry on in-cylinder fluid flows and equivalence ratio spread in a Direct Injection Spark Ignition Engine (DISI) during intake and compression stroke has been carried out. The analysis has been carried out using “STAR-CD es-ice” software for four piston top profiles viz., flat piston, flat piston with a centre bowl, dome piston with a central bowl and pentroof type piston with an offset bowl at an engine speed of 1000rpm. For meshing the geometric model, polyhedral trimmed cell are adopted. The solution is obtained by solving conservation of mass, momentum and energy equations using SIMPLE algorithm. From the results, it is found that for DISI engine, flat piston is best suitable.

Abstract. A new method of sea ice model evaluation is demonstrated. Data from the network of Arctic ice mass balance buoys (IMBs) are used to estimate distributions of vertical energy fluxes over sea ice in two densely sampled regions – the North Pole and Beaufort Sea. The resulting dataset captures seasonal variability in sea ice energy fluxes well, and it captures spatial variability to a lesser extent. The dataset is used to evaluate a coupled climate model, HadGEM2-ES (Hadley Centre Global Environment Model, version 2, Earth System), in the two regions. The evaluation shows HadGEM2-ES to simulate too much top melting in summer and too much basal conduction in winter. These results are consistent with a previous study of sea ice state and surface radiation in this model, increasing confidence in the IMB-based evaluation. In addition, the IMB-based evaluation suggests an additional important cause for excessive winter ice growth in HadGEM2-ES, a lack of sea ice heat capacity, which was not detectable in the earlier study. Uncertainty in the IMB fluxes caused by imperfect knowledge of ice salinity, snow density and other physical constants is quantified (as is inaccuracy due to imperfect sampling of ice thickness) and in most cases is found to be small relative to the model biases discussed. Hence the IMB-based evaluation is shown to be a valuable tool with which to analyse sea ice models and, by extension, better understand the large spread in coupled model simulations of the present-day ice state. Reducing this spread is a key task both in understanding the current rapid decline in Arctic sea ice and in constraining projections of future Arctic sea ice change.

ABSTRACT The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the ‘frozen-in’ approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β ≡ rt/rp = 5−7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

Abstract The 2010 UNPD’s Assessment of Development Results defined the Maldives “a vulnerable Small Island Developing State” by pointing out the influence of both external and local human factors on their fragile ecosystems. This impact is deeply related to a main geographical feature: the high dispersion of land mass and population, both of them spread over a distance of 860 km. Above all, this dispersion has an effect on two environmental issues: energy distribution and solid waste management. The latter is particularly interesting for the geographical analysis of Small Island Countries. Due to centre-periphery distance and cost benefits analysis, in the Maldives public and private actors have developed different solid waste management models: central and regional waste management dumpsites, hybrid systems implemented by resorts and “informal” practices still followed by local communities. In this paper, we discuss these systems stressing on the relevance of combining infrastructural measures with “informal” practices at local level. Furthermore, we report the outcomes of The Right Place, a participatory waste management action carried out by MaRHE Center (a Milano- Bicocca Research Center) in Faafu Magoodhoo Island.

With respect to mining sequence, this article intends to investigate the impact of pillarless centre-out stoping patterns (e.g. pyramidal sequences) on the performance of mine haulage drifts (e.g. ore access units), the tonnage of unmined ore at risk, and the required quantity of fill material. Using RS2D software, a two-dimensional, elasto-plastic finite-element model for a haulage drift located at 1200m below the surface in the orebody’s footwall has been built. The spread of yielding zones into the rock mass around an access drift and unmined stopes is used to assess mine haulage drift stability and estimate the amount of unmined ore at risk owing to local mining activity. The findings are presented and discussed in terms of the size of failure zones, the number of tonnes of unmined blocks at risk, and the amount of backfill materials required, all in relation to the mining stage. The findings show that haulage drift stability is rapidly diminishing. The drift roof begins to deteriorate at an early stage (after mining step 3). In the drift roof, left wall, floor, and right wall, failure zones measured 1.55m (step 3), 2.28m (step 4), 2.57m (step 5) and 1.88m (step 5) accordingly. After mining step 4, there was a total of 905 m3 of unmined ore at risk (4100 tons), and after mining step 5, a total of 1500 m3 (30 tons) of back fill material was required to strengthen stopes.

A body moves at uniform speed in an unbounded inviscid fluid. Initially, the body is infinitely far upstream of an infinite plane of marked fluid; later, the body moves through and distorts the plane and, finally, the body is infinitely far downstream of the marked plane. Darwin (1953) suggested that the volume between the initial and final positions of the surface of marked fluid (the drift volume) is equal to the volume of fluid associated with the ‘added-mass’ of the body.We re-examine Darwin's (1953) concept of drift and, as an illustration, we study flow around a sphere. Two lengthscales are introduced: ρmax, the radius of a circular plane of marked particles; and x0, the initial separation of the sphere and plane. Numerical solutions and asymptotic expansions are derived for the horizontal Lagrangian displacement of fluid elements. These calculations show that depending on its initial position, the Lagrangian displacement of a fluid element can be either positive – a Lagrangian drift – or negative – a Lagrangian reflux. By contrast, previous investigators have found only a positive horizontal Lagrangian displacement, because they only considered the case of infinite x0. For finite x0, the volume between the initial and final positions of the plane of marked fluid is defined to be the ‘partial drift volume’, which is calculated using a combination of the numerical solutions and the asymptotic expansions. Our analysis shows that in the limit corresponding to Darwin's study, namely that both x0 and ρmax become infinite, the partial drift volume is not well-defined: the ordering of the limit processes is important. This explains the difficulties Darwin and others noted in trying to prove his proposition as a mathematical theorem and indicates practical, as well as theoretical, criteria that must be satisfied for Darwin's result to hold.We generalize our results for a sphere by re-considering the general expressions for Lagrangian displacement and partial drift volume. It is shown that there are two contributions to the partial drift volume. The first contribution arises from a reflux of fluid and is related to the momentum of the flow; this part is spread over a large area. It is well-known that evaluating the momentum of an unbounded fluid is problematic since the integrals do not converge; it is this first term which prevented Darwin from proving his proposition as a theorem. The second contribution to the partial drift volume is related to the kinetic energy of the flow caused by the body: this part is Darwin's concept of drift and is localized near the centreline. Expressions for partial drift volume are generalized for flow around arbitrary-shaped two- and three-dimensional bodies. The partial drift volume is shown to depend on the solid angles the body subtends with the initial and final positions of the plane of marked fluid. This result explains why the proof of Darwin's proposition depends on the ratio ρmax/x0.An example of drift due to a sphere travelling at the centre of a square channel is used to illustrate the differences between drift in bounded and unbounded flows.

AbstractThe capability to determine the FCC-ee centre-of-mass energies (ECM) at the ppm level using resonant depolarization of the beams is essential for the Z line shape measurements, the W mass and the possible observation of the Higgs boson s-channel production. A first analysis (Blondel A et al Polarization and centre-of-mass energy calibration at FCC-ee. arXiv:1909.12245) demonstrated the feasibility of this programme, conditional to careful preparation and a number of further developments. The existing simulation codes must be unified; the analysis and design of the instrumentation must be developed; and a detailed planning must be developed for the simultaneous and coordinated operation of the accelerator, of the continuous polarization and depolarization measurements, and of the beam monitoring devices, ensuring a precise extrapolation from beam energies to centre-of-mass energy and energy spread.

We present observations with the Mid-InfraRed Instrument (MIRI) and Near-InfraRed Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST), targeting the extremely red quasar J165202.64+172852.3 at $z = 2.948$ (dubbed J1652). As one of the most luminous quasars known to date, it drives powerful outflows and hosts a clumpy starburst, in the midst of several interacting companions. We estimated the black hole (BH) mass of the system based on the broad and lines, as well as the broad emission in the infrared and in the ultraviolet. We recovered a very broad range of mass estimates, with individual constraints ranging between $ BH 9$ and $10.2$, which is extended further if we impose a uniform broad line region geometry at all wavelengths. The large spread may be caused by several factors: uncertainties on measurements (insufficient sensitivity to detect the broadest component of the faint Paschen beta line, spectral blending, ambiguities in the broad or narrow component distinction, etc.), lack of virial equilibrium, and uncertainties on the luminosity-inferred size of the broad line region (BLR). The exotic nature of our target (luminous, starburst, powerful outflows, high accretion rate, and dusty centre) is another likely contribution to the large uncertainties. We broadly constrained the stellar mass of J1652 by fitting the spectral energy distribution, which suggests that the host is extremely massive, at $ M_ with a $1.1$ dex uncertainty at $>1$ dex above the characteristic mass of the Schechter fit to the $z=3$ stellar mass function. Notably, J1652's central BH might be interpreted as being either over-massive or in line with the BH mass-stellar mass relation depending on the choice of assumptions. The recovered Eddington ratio varies accordingly, but it exceeds $10 <!PCT!>$ in any case. We set our results into context by providing an extensive overview and discussion of recent literature results and their associated assumptions. Our findings provide an important demonstration of the uncertainties inherent in the virial BH mass estimates of individual objects which are of particular relevance in the JWST era, given the increasing number of studies on rapidly accreting quasars at high redshift.

Ru(II) complexes, [Ru(bpy)2(m-R-L)](PF6)2 where bpy = 2,2’-bipyridyl and m-R-L= 1-(meta-R)-benzoyl-3-(pyridine-2-yl)-1H-pyrazole derivatives (R = H, CH3 and Cl) abbreviated as RuL, Ru(m-CH3-L) and Ru(m-Cl-L) complexes, respectively, were synthesized and characterized with spectroscopic techniques namely, infrared, UV-Vis and nuclear magnetic resonance (NMR), photoluminescence and mass spectroscopy. Density functional theory (DFT) and time-dependent (TD) DFT calculations were carried out to study the structural and electronic features of the molecules. These Ru(II) complexes exhibit photo-electronic properties required for a photosensitiser in a TiO2-catalysed photoelectrochemical (PEC) cell. In-depth understanding of the R-L fragment functionality is important to tune the photo-electronic properties of the Ru(II) complex. The highest-occupied molecular orbital (HOMO) is mainly localized at the Ru(II) centre, while the LUMO is dominantly spread across the R-L ligand. The Ru(II) complexes showed favourable metal-to-ligand charge transfer (MLCT) energy levels, which are comparably higher than the conduction band of TiO2 to facilitate electron injection process. Among the Ru(II) complexes, Ru(m-Cl-L) comparatively possesses the highest photoluminescence quantum yield and has the potential to be applied as photosensitiser in PEC systems.

AbstractThe Future Circular Collider (FCC-ee) offers the unique opportunity of studying the Higgs Yukawa coupling to the electron, $$y_\mathrm {e}$$ y e , via resonant s-channel production, $$\mathrm {e^+e^-}\rightarrow \mathrm {H}$$ e + e - → H , in a dedicated run at $$\sqrt{s} = m_\mathrm {H}$$ s = m H . The signature for direct Higgs production is a small rise in the cross sections for particular final states, consistent with Higgs decays, over the expectations for their occurrence due to Standard Model (SM) background processes involving $$\mathrm {Z}^*$$ Z ∗ , $$\gamma ^*$$ γ ∗ , or t-channel exchanges alone. Performing such a measurement is remarkably challenging for four main reasons. First, the low value of the e$$^\pm $$ ± mass leads to a tiny $$y_\mathrm {e}$$ y e coupling and correspondingly small cross section: $$\sigma _\mathrm {ee\rightarrow H} \propto m_\mathrm {e}^2 = 0.57$$ σ ee → H ∝ m e 2 = 0.57 fb accounting for initial-state $$\gamma $$ γ radiation. Second, the $$\mathrm {e^+e^-}$$ e + e - beams must be monochromatized such that the spread of their centre-of-mass (c.m.) energy is commensurate with the narrow width of the SM Higgs boson, $$\varGamma _\mathrm {H} = 4.1$$ Γ H = 4.1 MeV, while keeping large beam luminosities. Third, the Higgs mass must also be known beforehand with a few-MeV accuracy in order to operate the collider at the resonance peak, $$\sqrt{s} = m_\mathrm {H}$$ s = m H . Last but not least, the cross sections of the background processes are many orders-of-magnitude larger than those of the Higgs decay signals. A preliminary generator-level study of 11 Higgs decay channels using a multivariate analysis, which exploits boosted decision trees to discriminate signal and background events, identifies two final states as the most promising ones in terms of statistical significance: $$\mathrm {H}\rightarrow gg$$ H → g g and $$\mathrm {H}\rightarrow \mathrm {W}\mathrm {W}^*\!\rightarrow \ell \nu $$ H → W W ∗ → ℓ ν + 2 jets. For a benchmark monochromatization with 4.1-MeV c.m. energy spread (leading to $$\sigma _\mathrm {ee\rightarrow H} = 0.28$$ σ ee → H = 0.28 fb) and 10 ab$$^{-1}$$ - 1 of integrated luminosity, a $$1.3\sigma $$ 1.3 σ signal significance can be reached, corresponding to an upper limit on the e$$^\pm $$ ± Yukawa coupling at 1.6 times the SM value: $$|y_\mathrm {e}|<1.6|y^\mathrm {\textsc {sm}}_\mathrm {e}|$$ | y e | < 1.6 | y e S M | at 95% confidence level, per FCC-ee interaction point per year. Directions for future improvements of the study are outlined.

Le FCC-ee offre la possibilité de mesurer le couplage de Yukawa de l’électron via la production directe du Higgs dans le canal s à une énergie au centre de masse (CM) d’environ 125 GeV. Cette mesure est grandement facilitée si la dispersion en énergie au centre de masse des collisions électron-positron peut être réduite à un niveau comparable à la largeur naturelle du boson de Higgs dans le Modèle Standard, qui est de 4,1 MeV, sans perte substantielle de luminosité. Cette réduction de la dispersion en énergie des collisions est possible grâce au concept de « monochromatisation ». L’idée de base consiste à créer des corrélations opposées entre la position spatiale et la déviation en énergie au sein des faisceaux en collision, ce qui peut être réalisé en termes d’optique des faisceaux en introduisant une fonction de dispersion non nulle avec des signes opposés pour les deux faisceaux au point d’interaction. Depuis la première proposition en 2016, la mise en œuvre de la monochromatisation au FCC-ee a été continuellement améliorée, en commençant par des études paramétriques préliminaires. Dans cette thèse, une étude détaillée de la conception optique de la région d’interaction a été menée pour ce mode de collision nouvellement proposé, explorant différentes configurations potentielles et leur mise en œuvre dans le réseau global du FCC-ee, ainsi que des simulations de la dynamique des faisceaux et des évaluations de performance, incluant l’impact du « beamstrahlung »
The FCC-ee offers the potential to measure the electron Yukawa coupling via direct s-channel Higgs production at a centre-of-mass (CM) energy of about 125 GeV. This measurement is significantly facilitated if the CM energy spread of electron-positron collisions can be reduced to a level comparable to the Standard Model Higgs boson's natural width of 4.1 MeV without substantial loss in luminosity. Achieving this reduction in collision-energy spread is possible through the “monochromatization” concept. The basic idea consists of creating opposite correlations between spatial position and energy deviation within the colliding beams, which can be accomplished in beam-optics terms by introducing a nonzero dispersion function with opposite signs for the two beams at the interaction point. Since the first proposal in 2016, the monochromatization implementation at the FCC-ee has been continuously improved, starting from preliminary parametric studies. In this thesis, a detailed study of the interaction region optics design has been conducted for this newly proposed collision mode, exploring different potential configurations and their implementation in the FCC-ee global lattice, along with beam dynamics simulations and performance evaluations including the “beamstrahlung” impact