Stellar Dynamics at the Galactic Center with an Extremely Large Telescope

We discuss experiments achievable via monitoring of stellar dynamics near the massive black hole at the Galactic center with a next generation, extremely large telescope (ELT). Given the likely observational capabilities of an ELT and current knowledge of the stellar environment at the Galactic center, we synthesize plausible samples of stellar orbits around the black hole. We use the Markov Chain Monte Carlo method to evaluate the constraints that orbital monitoring places on the matter content near the black hole. Results are expressed as functions of the number N of stars with detectable orbital motions and the astrometric precision dtheta and spectroscopic precision dv at which stellar proper motions and radial velocities are monitored. For N = 100, dtheta = 0.5 mas, and dv = 10 km/s -- a conservative estimate of the capabilities of a 30 meter telescope -- the extended matter distribution enclosed by the orbits will produce measurable deviations from Keplerian motion if >1000 Msun is enclosed within 0.01 pc. The black hole mass and distance to the Galactic center will be measured to better than ~0.1%. Lowest-order relativistic effects, such as the prograde precession, will be detectable if dtheta < 0.5 mas. Higher-order effects, including frame dragging due to black hole spin, requires dtheta < 0.05 mas, or the favorable discovery of a compact, highly eccentric orbit. Finally, we calculate the rate at which monitored stars undergo detectable nearby encounters with background stars. Such encounters probe the mass function of stellar remnants that accumulate near the black hole. We find that ~30 encounters will be detected over a 10 yr baseline for dtheta = 0.5 mas.Comment: 14 pages, 5 figures; discussion no longer aperture-specific (TMT -> ELT), matches ApJ versio

Interruption of Tidal Disruption Flares By Supermassive Black Hole Binaries

Supermassive black hole binaries (SMBHBs) are products of galaxy mergers, and are important in testing Lambda cold dark matter cosmology and locating gravitational-wave-radiation sources. A unique electromagnetic signature of SMBHBs in galactic nuclei is essential in identifying the binaries in observations from the IR band through optical to X-ray. Recently, the flares in optical, UV, and X-ray caused by supermassive black holes (SMBHs) tidally disrupting nearby stars have been successfully used to observationally probe single SMBHs in normal galaxies. In this Letter, we investigate the accretion of the gaseous debris of a tidally disrupted star by a SMBHB. Using both stability analysis of three-body systems and numerical scattering experiments, we show that the accretion of stellar debris gas, which initially decays with time $\propto t^{-5/3}$, would stop at a time $T_{\rm tr} \simeq \eta T_{\rm b}$. Here, $\eta \sim0.25$ and $T_{\rm b}$ is the orbital period of the SMBHB. After a period of interruption, the accretion recurs discretely at time $T_{\rm r} \simeq \xi T_b$, where $\xi \sim 1$. Both $\eta$ and $\xi$ sensitively depend on the orbital parameters of the tidally disrupted star at the tidal radius and the orbit eccentricity of SMBHB. The interrupted accretion of the stellar debris gas gives rise to an interrupted tidal flare, which could be used to identify SMBHBs in non-active galaxies in the upcoming transient surveys.Comment: 13 pages, including one color figure; typos corrected; appeared in ApJ Letters (November 20 issue

Usvajanje prideva prostornih odnosa kod dece predškolskog i školskog uzrasta

The subject of this doctoral dissertation is the acquisition of spatial adjectives in the domain of physical space and abstract domain, as well as the acquisition of meaning of adjective antonym pairs in children of various ages. As children are older, and therefore linguistically and cognitively more developed, it could be expected the increase in a number of the total number of various adjectives that child uses. The acquisition of linguistic expressions for spatial coding is conditioned by the development of general cognitive abilities. The process of acquisition of abstract meaning of dimensional adjectives and meaning of opposites of these adjectives, as well as the speed at which these meanings are acquired, is presented through various development stages. We rely on Piaget's theory of cognitive development of language abilities which is based on empirically established facts. The applied method is the method of verbal associations by using the test of controlled and free word associations. The research was conducted on the child population of six and eight years of age. The results show that in the younger age most meanings were related to concrete physical space whereas in older ages abstract meanings were more often presented. Paradigmatic answers are present in larger numbers in an older age compared to a younger age which indicates a higher level of their language development. Children of an older age acquired more antonyms of spatial adjectives in relation to the children of a younger age. Better test results in all tests were achieved by children from the urban environment in comparison to children from rural environments. There is no difference between boys and girls when it comes to the adoption and understanding of the meaning of spatial adjectives

Influence of Oil Contamination on the Sea Surface Microlayer

Površinski mikrosloj mora (engl. sea surface microlayer; SSM) kao najveća granica faza ključno je područje u kojemu se odvijaju procesi izmjene između oceana i atmosfere, presudni za održavanje prirodne ravnoteže tvari na Zemlji. Ono je stanište morskog neustona, organizama prilagođenih životu na granici faza more-atmosfera uključujući i rane oblike života mnogih vrsta riba i školjaka. U tom relativno tankom sloju dolazi do koncentriranja prirodnih ali i mnogih antropogenih tvari koje tvore površinske filmove te utječu na fizikalno-kemijska i optička svojstva granice faza more-atmosfera. U novije vrijeme naftna onečišćenja oceana privlače pozornost javnosti diljem svijeta. U svjetska mora godišnje dospije oko 0,25% godišnje svjetske naftne proizvodnje, pri čemu je SSM pod izravnim utjecajem. Zagađenje SSM naftom ima velik toksični učinak na rane oblike života morskih organizama, što može kasnije bitno utjecati na morski hranidbeni lanac kao i smanjenje ulova komercijalnih vrsta u obalnim područjima. Također, naftni filmovi osjetno utječu na procese izmjene plinova materijala i energije između mora i atmosfere. Naftna onečišćenja morskog sustava čine opasnost, posebno za zatvorena i poluzatvorena morska područja, npr. Jadransko more, gdje djelovanje čovjeka može dovesti do katastrofalnih posljedica za cijeli morski ekosustav.Boundary layers between different environmental areas represent critical interfaces for biological, chemical and physical processes. The sea surface microlayer (SSM) as the uppermost 1-1000 µm forms the boundary layer interface between the atmosphere and ocean. It is now widely recognized that it plays a major role in the exchange of gases, material and energy. Also, it is a key interface for investigation of the fate and effects of airborne contaminants and particulate inputs into the sea, as well as for accumulation of dissolved pollutants. This thin layer is subject to many unique and dynamic, unbalanced processes such as wind stress, water transpiration, solar energy flux and atmospheric inputs. The SSM is also a unique ecosystem, an important habitat for marine neuston including fish eggs and larvae of many commercial species. It is rich in different natural and anthropogenic organic substances which are mostly surface active. The adsorbed organic substances form surfactant films and change physicochemical and optical properties of natural interface. The upper organic film of the SSM represents a sink for a range of pollutants, including chlorinated hydrocarbons, organotin compounds, petroleum hydrocarbons, polycyclic aromatic hydrocarbons and heavy metals. These pollutants can be enriched in the SSM by up to 104 times, relative to concentrations occurring in the underlying bulk water column. During the last few decades the marine oil pollution has become a matter of increasing international concern. Every year about 0.25 % of the world\u27s annual oil production ends up in the ocean affecting directly the SSM. Oil-polluted SSM is markedly toxic to fish eggs and larvae. Accumulation of organic pollutants from petroleum in the SSM has ecotoxicological impacts to the neustonic community including mortality, developmental abnormalities and depressed growth rates. These impacts produce dramatic effects on the marine food chain and reduce commercial catch of fish fishery recruitment in the coastal waters. Also, petroleum films can have a marked impact on exchange of heat, gases and particulate matter between the atmosphere and the ocean. It is a known fact that petroleum films due to the static effect retard evaporation, increase the temperature of the water surface film and decrease the aeration rate. Also, oil slicks are known to decrease turbulence at the interface, to damp wind-generated waves and to expert a strong effect on gas fluxes by hydrodynamic effects. Oil pollution of the SSM is extremely hazardous, especially to the closed and semi-closed costal marine environments, like the Adriatic Sea, where human influence may produce catastrophic effect on the whole marine ecosystem. A more systematic approach to research in physicochemical and biological processes of the SSM is needed for better understanding of this important environmental interface and its exact role in global distribution of human-borne contaminants

Influence of Oil Contamination on the Sea Surface Microlayer

Površinski mikrosloj mora (engl. sea surface microlayer; SSM) kao najveća granica faza ključno je područje u kojemu se odvijaju procesi izmjene između oceana i atmosfere, presudni za održavanje prirodne ravnoteže tvari na Zemlji. Ono je stanište morskog neustona, organizama prilagođenih životu na granici faza more-atmosfera uključujući i rane oblike života mnogih vrsta riba i školjaka. U tom relativno tankom sloju dolazi do koncentriranja prirodnih ali i mnogih antropogenih tvari koje tvore površinske filmove te utječu na fizikalno-kemijska i optička svojstva granice faza more-atmosfera. U novije vrijeme naftna onečišćenja oceana privlače pozornost javnosti diljem svijeta. U svjetska mora godišnje dospije oko 0,25% godišnje svjetske naftne proizvodnje, pri čemu je SSM pod izravnim utjecajem. Zagađenje SSM naftom ima velik toksični učinak na rane oblike života morskih organizama, što može kasnije bitno utjecati na morski hranidbeni lanac kao i smanjenje ulova komercijalnih vrsta u obalnim područjima. Također, naftni filmovi osjetno utječu na procese izmjene plinova materijala i energije između mora i atmosfere. Naftna onečišćenja morskog sustava čine opasnost, posebno za zatvorena i poluzatvorena morska područja, npr. Jadransko more, gdje djelovanje čovjeka može dovesti do katastrofalnih posljedica za cijeli morski ekosustav.Boundary layers between different environmental areas represent critical interfaces for biological, chemical and physical processes. The sea surface microlayer (SSM) as the uppermost 1-1000 µm forms the boundary layer interface between the atmosphere and ocean. It is now widely recognized that it plays a major role in the exchange of gases, material and energy. Also, it is a key interface for investigation of the fate and effects of airborne contaminants and particulate inputs into the sea, as well as for accumulation of dissolved pollutants. This thin layer is subject to many unique and dynamic, unbalanced processes such as wind stress, water transpiration, solar energy flux and atmospheric inputs. The SSM is also a unique ecosystem, an important habitat for marine neuston including fish eggs and larvae of many commercial species. It is rich in different natural and anthropogenic organic substances which are mostly surface active. The adsorbed organic substances form surfactant films and change physicochemical and optical properties of natural interface. The upper organic film of the SSM represents a sink for a range of pollutants, including chlorinated hydrocarbons, organotin compounds, petroleum hydrocarbons, polycyclic aromatic hydrocarbons and heavy metals. These pollutants can be enriched in the SSM by up to 104 times, relative to concentrations occurring in the underlying bulk water column. During the last few decades the marine oil pollution has become a matter of increasing international concern. Every year about 0.25 % of the world\u27s annual oil production ends up in the ocean affecting directly the SSM. Oil-polluted SSM is markedly toxic to fish eggs and larvae. Accumulation of organic pollutants from petroleum in the SSM has ecotoxicological impacts to the neustonic community including mortality, developmental abnormalities and depressed growth rates. These impacts produce dramatic effects on the marine food chain and reduce commercial catch of fish fishery recruitment in the coastal waters. Also, petroleum films can have a marked impact on exchange of heat, gases and particulate matter between the atmosphere and the ocean. It is a known fact that petroleum films due to the static effect retard evaporation, increase the temperature of the water surface film and decrease the aeration rate. Also, oil slicks are known to decrease turbulence at the interface, to damp wind-generated waves and to expert a strong effect on gas fluxes by hydrodynamic effects. Oil pollution of the SSM is extremely hazardous, especially to the closed and semi-closed costal marine environments, like the Adriatic Sea, where human influence may produce catastrophic effect on the whole marine ecosystem. A more systematic approach to research in physicochemical and biological processes of the SSM is needed for better understanding of this important environmental interface and its exact role in global distribution of human-borne contaminants

Safety assessment as a factor of national security strategy of the Republic of Serbia

У новијој историји неизвесност је постала норма понашања, а човечанство је под све већим притиском да пронађе ефикасније механизме заштите и успостављања безбеднијег света. Чини се да параметри глобалне структуре постају турбулентнији него икада, а нови облици међузависности све озбиљније мењају стереотипе у међународним односима. Праћење, разумевање и процењивање савремених трендова у међународним односима и геополитичких нужности, не само у релацијама одређеног простора, већ и у оквиру ширег окружења, важне су претпоставке безбедности државе. У процесу процењивања потребно је обухватити сва кључна питања која се рефлектују на безбедност државе, али и на остваривање националних циљева и интереса. Одувек је било присутно настојање држава да процене даљи развој цивилизације, односно релевантних међународних субјеката и њихово рефлектовање на националну безбедност. Адекватним процењивањем стварани су услови за превентивно деловање, одабир спољнополитичких инструмената и националних политика у циљу онемогућавања и спречавања изненађења односно ублажавања последица будућих догађаја. На нивоу државе врше се различите процене као што су економске, политичке, безбедносне, са циљем успешног развоја у свим областима друштвеног живота. При томе безбедносне процене имају примарни карактер јер се спроводе ради благовременог планирања, организовања и предузимања мера против разноврсних облика угрожавања безбедности државе. Међутим, погрешна је перцепција да се безбедносна процена бави искључиво безбедносним феноменом остављајући остале по страни. Управо безбедносна процена на нивоу државе повезује низ чињеница на економском, политичком, војном, међународном и другим подручјима људске делатности. Процењивање на нивоу државе није само себи циљ већ је у функцији планирања, и то свеобухватног, у процесном, просторном и временском смислу. Планирање и процењивање су активности које иду заједно јер се планирањем, уз коришћење резултата процењивања, и обратно, сагледавају унутрашњи и спољни токови, чиниоци и промене, а потом осмишљава најбољи одговор како би се превентивно ишло у сусрет догађајима и усмеравала активност државних органа на испуњењу одређених циљева. Поред тога, процењивање на нивоу државе има за циљ између осталог и усклађивање доктрине и стратегије безбедности са објективним условима угрожавања безбедности што се одражава и на дефинисање потребних мера на заштити имовине, људи, друштва и државе у целини. И поред неспорне чињенице да је свако предвиђање повезано са неизвесношћу и ризиком, то ни у ком случају не сме да буде препрека за развијање научног истраживања у овом домену. Евидентно је да се у домаћим научним и стручним радовима веома мало пажње посвећује безбедносном процењивању уопште. Међутим, предикција будућих догађаја је потребна многим субјектима националне безбедности који се у остваривању постављених циљава ослањају на предвиђање будућег развоја. То је уједно и потреба да се адекватно предвиди будући развој ситуације, а све у циљу планирања и преузимања одговорајућих мераIn recent history, uncertainty has become a norm of behavior, and humanity is under increasing pressure to find more effective mechanisms of protection and the establishment of a safer world. It seems that the parameters of the global structure are more turbulent than ever, and new forms of interdependence are more and more seriously changing stereotypes in international relations. Monitoring, understanding and assessment of contemporary trends in international relations and geopolitical necessity is an important assumption of state security, not just in the relations of a certain space, but also within the broader environment. The assessment process is necessary to include all the key issues that reflect on the security of the state, but also the accomplishment of national goals and interests. States’ efforts to assess the further development of civilization, relevant international subjects and their reflection on national security, have always been present. Adequate estimating created conditions for preventive action, appropriate selection of foreign policy tools and national policies in order to disable surprises and prevent or mitigate the effects of future events. At the state level are implemented various assessments such as economic, political and security with the aim of successful development in all spheres of social life. Security assessments have a primary character because they are untimely conducted for the planning, organization and implementation of measures against various forms of endangering state security. However, it is wrong perception that the security assessment deals only with security phenomenon, leaving the rest aside. Exactly security assessment on the state level connects a series of facts on the economic, political, military, international and other areas of human activities. It is precisely the security assessment at the state level that connects a number of facts in the economic, political, military, international and other areas of human activity. Assessing the level of the state is not a goal itself but in the function of comprehensive planning in the process, spatial and temporal terms, as well. Planning and assessment are activities which go together because the planning, using the assessment results and vice versa, perceives the internal and external flows, factors and changes, and then develops the best response to the preventively facing the events and directs activities of state organizations to fulfil certain goals. In addition, assessment at the state level aims inter alia the harmonization of doctrines and security strategy with the objective conditions of endangering the security which affects defining of the measures necessary to protect property, people, society and the state in total. IV Despite the indisputable fact that any prediction is associated with uncertainty and risk, this should in no case be an obstacle to the development of scientific research in this domain. It is obvious that in domestic scientific and professional papers, very little attention is devoted to security assessment in general. Yet, the prediction of future events is needed by many national security entities rely on anticipating future developments in achieving set goals. This is also the need to adequately anticipate the future development of the situation, all for the purpose of planning and taking the appropriate measure

Influence of toxic elements on enzyme activities in Plantago lanceolata and Taraxacum officinale rhizosphere and potential usage of plants in biomonitoring and phytoremediation

Doktorska disertacija predstavlja rezultat ispitivanja uticaja toksičnih elemenata na aktivnost enzima u rizosferi bokvice (Plantago lanceolata) i maslačka (Taraxacum officinale), kao i mogućnost upotrebe ovih biljaka u biomonitoringu i fitoremedijaciji. Istraživanje je izvršeno na području Bora i okoline na mestima uzorkovanja pod uticajem zagađenja iz topionice bakra, kao i sa flotacijskih jalovišta i odlagališta raskrivke. U uzorkovanom zemljištu određivane su fizičkohemijske osobine (pH vrednost, sadržaj vlage i organske materije, kao i granulometrijski sastav zemljišta), sadržaj elemenata (Al, Co, Cr, Cu, Fe, Mn, Ni, Pb i Zn), kao i aktivnost enzima u zemljištu (ß-glukozidaze, ureaze, arilsulfataze, kisele i alkalne fosfataze), dok je u uzorcima biljnog materijala analiziran sadržaj metala. Sadržaj elemenata u zemljištu koji je prelazio zakonom definisane granične i remedijacione vrednosti, kao i visoke vrednosti faktora kontaminacije i obogaćenja zemljišta, naročito za Cu, Pb i Zn, ukazale su da su mesta u neposrednoj blizini topionice, kao i na pravcima dominantnih vetrova pod uticajem zagađenja emitovanog tokom pirometalurške proizvodnje bakra. Ispitivanja su pokazala značajan uticaj fizičko-hemijskih osobina (naročito pH vrednosti) zemljišta i sadržaja elemenata na aktivnost enzima u rizosferi bokvice i maslačka, pri čemu aktivnost arilsulfataze ima potencijala za upotrebu u indikaciji zagađenja. Analiza koncentracija elemenata u biljnom materijalu ukazala je na mogućnost upotrebe ovih biljaka (naročito nadzemnih delova) u biomonitoringu. Bokvica i maslačak nisu pokazali potencijal za upotrebu u fitoremedijaciji (izuzev bokvice za fitostabilizaciju Zn), pri čemu je kod obe biljne vrste uočena ekskluzija elemenata.The doctoral dissertation represents the results of investigating the influence of toxic elements on enzyme activities in ribwort plantain (Plantago lanceolata) and dandelion (Taraxacum officinale) rhizosphere, as well as the possibilities of using these plants in biomonitoring and phytoremediation. The research was conducted in Bor and its surroundings at the sampling sites under the influence of pollution from the copper smelter, as well as flotation tailings ponds and overburden dumps. Physico-chemical properties (pH value, content of moisture and organic matter, and soil texture), the content of the elements (Al, Co, Cr, Cu, Fe, Mn, Ni, Pb i Zn), as well as soil enzyme activities (ß-glucosidase, urease, arylsulphtase, acid and alkaline phosphatase) were determined in the sampled soil, while the content of the metals was analyzed in plant material. The content of the elements in soil which exceeded the limit and remediation values defined by the Serbian Regulation, as well as high values of soil contamination and enrichment, especially for Cu, Pb and Zn, indicated that the sampling sites in the vicinity of the smelter, as well as in the prevailing wind directions were under the influence of the pollution originating from the pyrometallurgical copper production. The investigations showed a significant influence of soil physico-chemical properties (especially soil pH value) and soil elemental content on the enzyme activities in ribwort plantain and dandelion rhizosphere, whereby arylsulphatase activity had the potential for usage in pollution indication. The analysis of the content of the elements in the plant material showed the potential for usage of the selected plant (especially aboveground parts) in biomonitoring. Ribwort plantain and dandelion did not show the potential for usage in phytoremediation (except ribwort plantain for phytostabilization of Zn), whereby in both plant species the exclusion of the elements was observed

Long Term Evolution of Massive Black Hole Binaries

The long-term evolution of massive black hole binaries at the centers of galaxies is studied in a variety of physical regimes, with the aim of resolving the ``final parsec problem,'' i.e., how black hole binaries manage to shrink to separations at which emission of gravity waves becomes efficient. A binary ejects stars by the gravitational slingshot and carves out a loss cone in the host galaxy. Continued decay of the binary requires a refilling of the loss cone. We show that the standard treatment of loss cone refilling, derived for collisionally relaxed systems like globular clusters, can substantially underestimate the refilling rates in galactic nuclei. We derive expressions for non-equilibrium loss-cone dynamics and calculate time scales for the decay of massive black hole binaries following galaxy mergers, obtaining significantly higher decay rates than heretofore. Even in the absence of two-body relaxation, decay of binaries can persist due to repeated ejection of stars returning to the nucleus on eccentric orbits. We show that this recycling of stars leads to a gradual, approximately logarithmic dependence of the binary binding energy on time. We derive an expression for the loss cone refilling induced by the Brownian motion of a black hole binary. We also show that numerical N-body experiments are not well suited to probe these mechanisms over long times due to spurious relaxation.Comment: Replaced to match the accepted version, ApJ, 596 (2003

What is L*?: Anatomy of the Galaxy Luminosity Function

Using the empirical relations between the central galaxy luminosity and the halo mass, and between the total galaxy luminosity in a halo and the halo mass, we construct the galaxy luminosity function (LF). To the luminosity of the central galaxy in a halo of a given mass we assign log-normal scatter with a mean calibrated against the observations. In halos where the total galaxy luminosity exceeds that of the central galaxy, satellite galaxies are distributed as a power-law in luminosity. Combined with the halo mass function, this description reproduces the observed characteristics of the galaxy LF, including a shape consistent with the Schechter function. When all galaxies are included, regardless of the environment or the Hubble type, the Schechter L* is the luminosity scale above which the central galaxy luminosity-halo mass relation flattens; L* corresponds to ~10^{13}Msun on the halo mass scale. In surveys where central galaxies in massive clusters are neglected, either by design or because of the cosmic variance, L* is simply the mean luminosity of central galaxies in halos at the upper end of the selected mass range. The smooth, exponential decay of the Schechter function toward high luminosities reflects the intrinsic scatter in the central galaxy luminosity-halo mass relation. In addition to the LF, the model successfully reproduces the observed dependence of galaxy clustering bias on luminosity.Comment: 4 pages, 5 figures, updated figure 2b and the related discussion to correct for difference in Hubble constant between data and mode