1,416 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.
Electrochemical Reduction of Trinitrotoluene on a Modified Platinum Electrode
Poster presented at the 61st Annual Meeting of the International Society of Electrochemistry, Nice, France, September 26 ā October 1, 201
On Orbits for a Particular Case of Axial Symmetry
A particular case of steady state and axial symmetry - the potentialformula proposed by Miyamoto and Nagai - is studied. A number of orbits of abound test particle is determined numerically, with both, the potentialparameters and initial conditions, varied. Unlike special cases, such asnearly circular and nearly planar orbits, in the case of "truly spatial orbits" the time dependence of the coordinates becomes very complicated and amathematical treatment including any known periodic functions is hardlypossible. Bearing in mind that orbits studied in the present paper aredetermined by three elements, the authors propose the mean values over time ofthe squares of velocity components to characterize them
Flora of the city of Podgorica, Montenegro: Taxonomic analysis
In this paper we present the taxonomic segment of a floristic study undertaken in the city of Podgorica in the period of 2002-2007. The check-list of spontaneously growing vascular plants includes 1227 species and subspecies belonging to 545 genera and 118 families. The dominant families are Poaceae (11.7%), asteraceae (11.2%) and Fabaceae (9.2%). The most abundant genera are Trifolium (2.1%), Euphorbia (1.5%), Carex (1.5%), Bromus (1.3%) and Vicia (1.2%). Analysis of the flora of Podgorica in comparison with some other european cities showed that the flora of Podgorica is most similar to that of Rome (Q/S= 0,7)
Flora of the city of Podgorica, Montenegro: Chorologic structure and comparison with the floras of Rome, Patras, and Salonika
Research on the geographical structure of the flora of Podgorica revealed that 85.9% of the species are native, while 14.1% are non-native. This ratio is typical of Mediterranean settlements, where even the most urbanized region reflects the overall character of the surrounding flora. In terms of chorologic groups, the three largest are: eury-Mediterranean (18.2%), cosmopolitan (12.6%), and steno-Mediterranean (8.3%). The percentage of endemic and subendemic plants is also significant (6.8%). Within the group of aliens, species of Asian origin prevail. Comparative analysis of the chorologic spectra of Podgorica, Rome, Patras, and Salonika revealed some similarities
Motorne funkcije i kognicija kod starih osoba
The prolonging of a lifespan and the increasing proportion of elderly people in general population are setting new healthcare tasks. One of them is researching and clarifying the relations and links between motoric and cognitive functions in elderly. 'Impoverishment' of cognitive capacities occurs during the aging process. Many studies show a strong link between cognition and the function of walking. There is growing evidence that the decline in cognitive functions is resulting in deterioration of walking. Usually described as characteristic of the later stages of dementia, the distortion of ambulation may also be present in the earlier stages, even before the prodromal stage of mild cognitive impairment. Speed and temporal and spatial variability of steps are the main gait characteristics which are connected to the degree of decline in cognitive processes. Those characteristics are motor phenotype that reflects the deterioration of cognitive performance and which can be used for prediction of dementia. It is assumed that physical activity provides beneficial effects at cognitive and psychological levels, including prevention and improvement of depressive states and anxiety disorders, enhancing stress reduction, improved self-confidence and above all it delays cognitive decline in the elderly. Disruption of axons and myelin in the cerebral white matter is considered one of the primary mechanisms underlying age-related cognitive decline. Therefore, maintaining white matter structural connectivity in the old age may be one of the key factors in preserving brain function and high cognitive performance necessary for independent living. Physical activity also influences cerebrovascular mechanisms, such as preserving higher blood vessel elasticity and wall integrity. Moreover, there is an association between light physical activity and white matter integrity especially in the temporal lobe. The conclusion of some studies shows a relationship between the Īµ4 allele and brain derived neurotrophic factor (BDNF) response to physiologic adaptation which likely impacts the extent of neuroprotective benefit gained from engagement in physical exercise. Some authors propose a program of exercises which consist of a combined aerobic and resistance training. Motoric function and cognition are closely related and using regular physical activity is important for maintaining physical and mental health in the elderly.Produžetak životnog veka i poveÄanje udela starijih ljudi u opÅ”toj populaciji postavlja nove zadatke za zdravstvene službe. Jedan od njih je istraživanje i razjaÅ”njavanje odnosa i povezanosti izmeÄu motoriÄkih i kognitivnih funkcija kod osoba starijeg životnog doba. Tokom procesa starenja odigrava se 'osiromaÅ”enje' kognitivnih kapaciteta. Mnoge studije ukazuju na postojanje izrazite povezanosti izmeÄu kognitivnih funkcija i funkcije hoda. Postoji sve viÅ”e dokaza da opadanje kognitivnih funkcija rezultuje deterioracijom funkcije hoda. PoremeÄaj funkcije hoda se obiÄno povezuje sa kasnijim stadijumima demencije, meÄutim, ona može biti naruÅ”ena i u ranijim stadijumima pa Äak i pre nastanka prodromalnog stadijuma tj. blagog kognitivnog poremeÄaja. Brzina koraka i vremenska i prostorna varijabilnost koraka su glavne karakteristike koje se povezuju sa stepenom pada kognitivnih procesa. Ove karakteristike su motorni fenotip koji reflektuje stepen deterioracije kognitivnog funkcionisanja i koji može biti upotrebljen kao prediktivni pokazatelj nastanka demencija. Pretpostavlja se da fiziÄka aktivnost obezbeÄuje pozitivne efekte na kognitivnom i psiholoÅ”kom planu, ukljuÄujuÄi prevenciju i poboljÅ”anje depresivnih i anksioznih stanja, da redukuje stres, unapreÄuje samopouzdanje i konaÄno, odlaže nastanak procesa opadanja kognitivnih funkcija kod osoba starijeg doba. Prekidi aksonskih puteva i mijelina u beloj masi se smatraju jednim od primarnih mehanizama za nastanak opadanja kognitivnih funkcija tokom procesa starenja. Zbog toga se pretpostavlja da je održavanje strukturalne celovitosti bele mase jedan od kljuÄnih faktora koji doprinose oÄuvanju viÅ”ih kognitivnih funkcija koje su neophodne za nezavisno funkcionisanje u starijem životnom dobu. FiziÄka aktivnost takoÄe deluje preko cerebrovaskulnih mehanizama kao Å”to su oÄuvanost elastiÄnosti i integriteta zidova krvnih sudova. Osim pomenutog, postoji povezanost izmeÄu lagane fiziÄke aktivnosti i integriteta bele mase posebno u temporalnom lobusu. ZakljuÄci pojedinih istraživanja ukazuju na postojanje odnosa izmeÄu Īµ4 genskog alela i brain derived neurotrophic factor (BDNF) odgovora na fizioloÅ”ku adaptaciju nastalu fiziÄkim vežbanjem, za koju se pretpostavlja da pozitivno utiÄe na neuroprotekciju. Neki autori predlažu program fiziÄkog vežbanja kao kombinaciju aerobnog i treninga sa primenjenim otporom. MotoriÄka funkcija i kognicija su blisko poezani, a redovna fiziÄka aktivnost i vežbanje je važno za održavanje fiziÄkog i mentalnog zdravlja
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