569 research outputs found
Addressing the missing matter problem in galaxies through a new fundamental gravitational radius
We demonstrate that the existence of a Noether symmetry in theories of
gravity gives rise to a further gravitational radius, besides the standard
Schwarzschild one, determining the dynamics at galactic scales. By this
feature, it is possible to explain the baryonic Tully-Fisher relation and the
rotation curve of gas-rich galaxies without the dark matter hypothesis.Comment: 9 pages, 2 figures, to be published in JCA
Recovering the fundamental plane of galaxies by gravity
The fundamental plane (FP) of galaxies can be recovered in the framework of
gravity avoiding the issues related to dark matter to fit the
observations. In particular, the power-law version , resulting
from the existence of Noether symmetries for , is sufficient to implement
the approach. In fact, relations between the FP parameters and the corrected
Newtonian potential, coming from , can be found and justified from a
physical point of view. Specifically, we analyze the velocity distribution of
elliptical galaxies and obtain that , the scale-length depending on the
gravitational system properties, is proportional to , the galaxy effective
radius. This fact points out that the gravitational corrections induced by
can lead photometry and dynamics of the system. Furthermore, the main
byproduct of such an approach is that gravity could work in different ways
depending on the scales of self-gravitating systems.Comment: 18 pages, 3 tables, 8 figures. Accepted for publication in Phys. Dark
Univers
Constraining Extended Gravity Models by S2 star orbits around the Galactic Centre
We investigate the possibility to explain theoretically the observed
deviations of S2 star orbit around the Galactic Centre using gravitational
potentials derived from modified gravity models in absence of dark matter. To
this aim, an analytic fourth-order theory of gravity, non-minimally coupled
with a massive scalar field is considered. Specifically, the interaction term
is given by analytic functions and where is the Ricci
scalar and is a scalar field whose meaning can be related to further
gravitational degrees of freedom. We simulate the orbit of S2 star around the
Galactic Centre in (Yukawa-like) and (Sanders-like) gravity
potentials and compare it with NTT/VLT observations. Our simulations result in
strong constraints on the range of gravity interaction. In the case of analytic
functions , we are not able to obtain reliable constraints on the
derivative constants and , because the current observations of S2
star indicated that they may be highly mutually correlated. In the case of
analytic functions , we are able to obtain reliable constraints on
the derivative constants , , , , and
. The approach we are proposing seems to be sufficiently reliable
to constrain the modified gravity models from stellar orbits around Galactic
Centre.Comment: 9 pages, 6 figure to appear in Phys. Rev.
Masses of constituent quarks confined in open bottom hadrons
We apply color-spin and flavor-spin quark-quark interactions to the meson and
baryon constituent quarks, and calculate constituent quark masses, as well as
the coupling constants of these interactions. The main goal of this paper was
to determine constituent quark masses from light and open bottom hadron masses,
using the fitting method we have developed and clustering of hadron groups. We
use color-spin Fermi-Breit (FB) and flavor-spin Glozman-Riska (GR) hyperfine
interaction (HFI) to determine constituent quark masses (especially quark
mass). Another aim was to discern between the FB and GR HFI because our
previous findings had indicated that both interactions were satisfactory. Our
improved fitting procedure of constituent quark masses showed that on average
color-spin (Fermi-Breit) hyperfine interaction yields better fits. The method
also shows the way how the constituent quark masses and the strength of the
interaction constants appear in different hadron environments.Comment: 15 pages, 6 tables, 1 figure. Accepted for publication in Mod. Phys.
Lett.
Constraining Non-local Gravity by S2 star orbits
Non-local theories of gravity have recently gained a lot of interest because
they can suitably represent the behavior of gravitational interaction in the
ultraviolet regime. Furthermore, at infrared scales, they give rise to notable
cosmological effects which could be important to describe the dark energy
behavior. In particular, exponential forms of the distortion function seem
particularly useful for this purpose. Using Noether Symmetries, it can be shown
that the only non-trivial form of the distortion function is the exponential
one, which is working not only for cosmological mini-superspaces, but also in a
spherically symmetric spacetime. Taking this result into account, we study the
weak field approximation of this type of non-local gravity, and comparing with
the orbits of S2 stars around the Galactic center (NTT/VLT data), we set
constraints on the parameters of the theory. Non-local effects do not play a
significant role on the orbits of S2 stars around Sgr A*, but give richer
phenomenology at cosmological scales than the CDM model. Also, we show
that non-local gravity model gives better agreement between theory and
astronomical observations than Keplerian orbits.Comment: 11 pages, 6 figures. Accepted for publication in Phys. Rev.
Influence of the building energy efficiency on indoor air temperature: The case of a typical school classroom in Serbia
Greenhouse gases emission as well as total energy consumption in buildings of public importance, such as schools, municipal buildings, health care centers, can be significantly reduced by increasing buildings’ energy efficiency. Buildings’ energy consumption adds up to 37% of total energy consumption in the EU countries. In the Republic of Serbia this amount is significantly higher, about 50%. School buildings are considered as one of the most diverse structures from the point of energy-efficient design and construction. The main aim of this paper is to determine the most appropriate settings for possible improvements in energy efficiency and temperature comfort inside a typical primary school classroom in Serbia. The energy efficiency analysis was performed during the heating season for the naturally ventilated primary school classroom located in the eastern Serbia region. The analysis was performed using novel CFD model, suggested in this paper. The suggested model was used to solve two hypothetical scenarios. The first scenario simulates the temperature field in classroom with current energy characteristic envelope of the school building. The calculated numerical data from the first scenario were compared with in-situ measurements values of temperature and wall heat fluxes and showed satisfying accuracy. The second scenario was simulated to indicate possible improvements, which would allow energy consumption decrease and thermal quality enhancement. The analyzed results, calculated using the suggested numerical model under the second scenario conditions, showed that using appropriate set of measures, it is possible to obtain desired temperature comfort levels without need for increase in the building energy consumption
Smart capacitive moisture sensor calibration in mineral wool and green roof soil substrate
The environmental benefits of green roofs have been widely recognized. In recent years, increasing attention has been paid to moisture management in the green roof systems. The moisture in the green roof has an influence on its thermal and hydrological performances. An accurate measurement of water content in green roof substrate is important for irrigation monitoring, optimal irrigation management, and plant growth. Knowing the performance and characteristics of the sensor for the chosen substrate layer in a green roof system is essential. This paper presents laboratory calibration of the capacitive moisture sensor in two types of the green roof substrate layer. The volumetric water content of several mineral wool and soil samples, with the water content from low until saturated, were measured using the gravimetric method and related to frequency obtained by the sensor. The results have shown that the capacitive moisture sensor has a good response to water content variation
Antimicrobial activity of chitosan coatings and films against Listeria monocytogenes on black radish
AbstractThe antibacterial activity of chitosan coatings prepared with acetic or lactic acid, as well as of composite chitosan–gelatin films prepared with essential oils, was evaluated in fresh shredded black radish samples inoculated with Listeria monocytogenes ATCC 19115 and L. monocytogenes ATCC 19112 during seven days of storage at 4°C. The chitosan coating prepared with acetic acid showed the most effective antibacterial activity. All tested formulations of chitosan films exhibited strong antimicrobial activity on the growth of L. monocytogenes on black radish, although a higher inhibition of pathogens was achieved at higher concentrations of chitosan. The antimicrobial effect of chitosan films was even more pronounced with the addition of essential oils. Chitosan–gelatin films with thyme essential oils showed the most effective antimicrobial activity. A reduction of 2.4log10CFU/g for L. monocytogenes ATCC 19115 and 2.1log10CFU/g for L. monocytogenes ATCC 19112 was achieved in the presence of 1% chitosan film containing 0.2% of thyme essential oil after 24h of storage
LR and L+R Systems
We consider coupled nonholonomic LR systems on the product of Lie groups. As
examples, we study -dimensional variants of the spherical support system and
the rubber Chaplygin sphere. For a special choice of the inertia operator, it
is proved that the rubber Chaplygin sphere, after reduction and a time
reparametrization becomes an integrable Hamiltonian system on the
--dimensional sphere. Also, we showed that an arbitrary L+R system
introduced by Fedorov can be seen as a reduced system of an appropriate coupled
LR system.Comment: 18 pages, 1 figur
Coefficient stability of operator–difference schemes
A priori estimates expressing continuous dependence of the solution of a first order evolutionary equation in Hubert space on initial condition, right hand side and operator perturbations are obtained in time–integral norms. Analogous results hold for corresponding finite difference schemes.
Operatorinių-diferencialinių schemų koeficientis stabilumas
Santrauka
Darbe tiriamas pirmosios eiles nestacionariu diferencialiniu lygčiu, apibrežtu Huberto erdvese, stabilumas pradines salygos, laisvuju nariu ir operatoriaus koeficientu atžvilgiu. Stabilumo iverčiai irodomi integralinese laiko atžvilgiu normose. Analogiški rezultatai gauti ir baigtiniu skirtumu schemoms. Irodyti stipraus stabilumo iverčiai, kai modifikuojami lygties operatorius ir pradine salyga. Teoriniai rezultatai pritaikyti vienmačiam šilumos laidumo uždaviniui ir ji aproksimuojančiai baigtiniu skirtumu schemai.
First Published Online: 14 Oct 201
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