Initial Mass Distribution Research Articles

Modeling the performance of two-bed, sillica gel-water adsorption chillers

This article presents a transient model for a two-bed, silica gel-water adsorption chiller. Compared with our previous cyclic-steady-state model, we found very good agreement between our model prediction and experimental data. We found that, regardless of the initial mass distribution, the chiller was able to achieve the same cyclic-steady-state within four cycles or 1800 s. We also demonstrated that the manufacturer had empirically evolved to select a fixed switching and cycle time such that the best peak evaporator temperature suppression, and near maximum cooling capacity can be achieved by a compact design.

Smoluchowski's coagulation equation: uniqueness, nonuniqueness and a hydrodynamic limit for the stochastic coalescent

Sufficient conditions are given for existence and uniqueness in Smoluchowski's coagulation equation, for a wide class of coagulation kernels and initial mass distributions. An example of nonuniqueness is constructed. The stochastic coalescent is shown to converge weakly to the solution of Smoluchowski's equation.

A monte carlo simulation of the depolymerization of linear homopolymers by endo-enzymes exhibiting random-attack probability and single-attack mechanism: application to the (1-->3), (1-->4)-beta-D-glucan/endo-(1-->3),(1-->4)-beta-D-glucanase system

A Monte Carlo simulation of the depolymerization of linear homopolymers by specific endo-enzymes exhibiting random-attack probability and a single-attack mechanism has been developed. The program simulates the "real" depolymerization versus time of a polydisperse sample of substrate by a specific endo-enzyme. Given the initial mass distribution and concentration of the substrate, the initial concentration of the enzyme, and its Michaelis-Menten constant, the program simulates the evolution of the mass distribution of the substrate with the depolymerization time. When tested against experimental data from the depolymerization of barley (1-->3),(1-->4)-beta-D-glucan by malt endo-(1-->3), (1-->4)-beta-D-glucanase, monitored using the Calcofluor-FIA method with fluorescent detection, excellent results were obtained. Copyright 1998 John Wiley & Sons, Inc.

Binaries in Globular Clusters

Binary stars in a globular cluster (hereafter, GC) may be primordial (i.e. formed along with the cluster), or the result of cluster dynamics. “Dynamical” binaries can result from conservative three-body encounters (e.g. Spitzer, 1987) if a third star can carry away enough kinetic energy to leave two others bound, or from dissipative two-body encounters, if two stars happen to pass within a few stellar radii of one other (Fabian, Pringle, & Rees, 1975). Such non-primordial systems are likely to be found primarily in evolved GC cores, both because conditions are more favorable for making them there, and because of mass segregation. Knowledge of the formation process allows reasonable estimates to be made of their mass and energy distributions. The initial spatial, mass, and energy distributions of primordial binaries, on the other hand, are largely unknown.

Hard X‐Rays and Gamma Rays from Type Ia Supernovae

The γ-ray light curves and spectra are presented for a set of theoretical Type Ia supernova (SN Ia) models including deflagration, detonation, delayed detonation, and pulsating delayed detonations of Chandrasekhar-mass white dwarfs, as well as merger scenarios that may involve more than the Chandrasekhar mass and helium detonations of sub-Chandrasekhar-mass white dwarfs. The results have been obtained with a Monte Carlo radiation transport scheme that takes into account all relevant γ-transitions and interaction processes. The result is a set of accurate line profiles that are characteristic of the initial 56Ni mass distribution of the supernova models. The γ-rays probe the isotopic rather than merely the elemental distribution of the radioactive elements in the ejecta. Details of the line profiles (including the line width, shift with respect to the rest frame, and line ratios) are discussed. With sufficient energy and temporal resolution, different model scenarios can clearly be distinguished. Observational strategies are discussed for current and immediately upcoming generations of satellites (Compton Gamma Ray Observatory [CGRO] and International Gamma-Ray Astrophysical Laboratory [INTEGRAL]), as well as projected future missions including presently unavailable equipment such as Laue telescopes. With CGRO, it is currently possible with sufficiently early observations (near optical maximum) to distinguish helium detonations from explosions of Chandrasekhar-mass progenitors and of those involving mergers up to a distance of about 15 Mpc. This translates into one target of opportunity every 8 years. SNe Ia up to about 10 Mpc would allow detailed CGRO studies of line ratios of 56Co lines. INTEGRAL will be able to perform detailed studies of the 56Co line profiles with a range comparable to CGRO. The superior sensitivity of INTEGRAL for low energies makes detection and detailed study of the positron annihilation line and appropriate low-energy 56Ni lines possible up to about 10-15 Mpc for all models. This capability means that this lower energy range may be the most useful for INTEGRAL detection and study of SNe Ia. Such studies will allow the determination of the precise time of the explosion. Whereas the current generation of γ-ray detectors will allow the study of supernovae that are discovered by other means, a new generation of proposed γ-ray detectors with sensitivity of about 10-6 photons s-1 cm-2 would generate the opportunity to discover supernovae by their γ-ray emission up to a distance of ≈ 100 Mpc. This would allow a systematic study of the variety of SNe Ia in terms of their γ-ray properties, independent of their optical properties. In addition, since γ-rays are not obscured by the host galaxy, such experiments would, for the first time, provide absolute supernova rates. Relative rates as a function of the morphology of and position in the host galaxy could be studied directly.

Fortification of Sugar with Vitamin A

The technology for fortifying sugar with vitamin A was developed in Guatemala in the mid-1970s, and the Guatemalan government enacted legislation to make fortification mandatory in June 1974. This action was copied by other Central American governments. The fortification programme in Guatemala developed in two stages. In the first (1975–77), the fortification programme was evaluated four times at six-month intervals and was shown to be effective. The sugar industry was responsible for carrying out the programme, but the programme was suspended, mainly because of economic arguments. After 10 years of effort, the programme was restarted in 1989. At this time the programme was combined with an initial mass distribution of vitamin A capsules to pre-school children, which began the first successful social mobilization effort in the area. The programme was evaluated for six months and was shown to be effective in improving the vitamin A status of the Guatemalan population. This sec- ond stage has been active continuously since 1989. With improvements in the technology of fortification, new approaches have been tested, and now it is possible to obtain an excellent sugar doubly fortified with vitamin A and iron, using new iron products of high bioavailability that do not alter the organoleptic characteristics of the sugar and do not produce unwanted colour changes during processing. To avoid the rancidity of premixes, new processes of dry mixing have been developed in which no oil is used, This opens a real possibility for the fortification of sugar with other nutrients. Sugar fortified with vitamin A, iron, and zinc, either alone or in any combination, is commercially available in Brazil, where, under the guidance of the Latin American Centre of Nutrition and Metabolic Studies (CELANEM), the procedures have been developed using iron amino acid chelated minerals.

Globular cluster evolution in M87 and fundamental plane ellipticals

The globular cluster population in M87 has decreased measurably through dynamical evolution caused by relaxation, binary heating and time-dependent tidal perturbation. For fundamental plane ellipticals in general, cluster populations evolve more rapidly in smaller galaxies because of the higher mass density. A simple evolutionary model reproduces the observed trend in specific frequency with luminosity for an initially constant relationship. Fits of theoretically evolved populations to M87 cluster data from McLaughlin et al. (1994) show the following: 1) dynamical effects drive evolution in the initial mass and space distributions and can account for the large core in the spatial profile as well as producing radial-dependence in the mass spectrum; 2) evolution reduces S_N by 50% within 16 kpc and 35% within 50 kpc, implying that S_N was initially 26 in this region. We estimate that 15% of the `missing' clusters lie below the detection threshold with mass less than 10^5 M_sun.

A Universal Formation Mechanism for Open and Globular Clusters in Turbulent Gas

A universal mechanism for cluster formation in all epochs and environments is found to be consistent with the properties and locations of young and old globular clusters, open clusters and unbound associations, and interstellar clouds. The primary structural differences between various cluster types result from differences in pressure at the time of formation, combined with different ages for subsequent evolution. All clusters begin with a mass distribution similar to that for interstellar clouds, which is approximately n(M)dM M-2 dM. Old halo globulars have a current mass distribution that falls off at low mass because of a Hubble time of cluster destruction. Young globulars have not yet had time for a similar loss, and some old open clusters have survived because of their low densities. The peak in the halo cluster luminosity function depends only on age, and is independent of the host galaxy luminosity, as observed. The peak globular cluster mass is not a characteristic or Jeans mass in the primordial galaxy, as previously suggested. The initial mass distribution functions for young and old globular clusters, open clusters and associations, and interstellar clouds are all power laws with a slope of ~ -2. This distribution could be the result of fractal structure in turbulent gas. New data on clusters in the LMC also follow this power law. The slope is so steep that it implies a significant fraction of star formation occurs in small clusters. Numerous halo field stars should come from the evaporation of small halo clusters, and a high fraction of disk field stars should arise in small unbound disk clusters. This differs significantly from previous suggestions that most disk stars form in large OB associations. Globular clusters of all ages preferentially form in high-pressure regions. This is directly evident today in the form of large kinematic pressures from the densities and relative velocities of member stars. High pressures at the time of globular cluster formation are either the result of a high background virial density in that part of the galaxy (as in dwarf galaxies or galactic nuclei and nuclear rings), turbulence compression (in halo globulars), or large-scale shocks (in interacting galaxies). Massive clusters that form in such high-pressure environments are more likely to be bound than low-mass clusters or clusters of equal mass in low-pressure regions. This is because virialized clouds are more tightly bound at high pressure. A simple model illustrates this effect. One implication of this result is that starburst regions preferentially make globular clusters, in which case some elliptical galaxies could have formed by the violent merger of spiral galaxies.

Analytical Solution of the Multicomponent Aerosol General Dynamic Equation—without Coagulation

ABSTRACT An analytical analysis of multicomponent aerosol dynamics is presented. The analysis is applicable for linear as well as nonlinear condensation—evaporation rates and for any type of initial size—mass distribution. The effects of growth and removal are described, while the influence of particle coagulation is not considered. The analytical solution can be of use for describing the evolution of an initial mass distribution representing a multicomponent aerosol where each species grows-evaporates at a different rate.

Aggregation dynamics in a self-gravitating one-dimensional gas

Aggregation of mass by perfectly inelastic collisions in a one-dimensional self-gravitating gas is studied. The binary collisions are subject to the laws of mass and momentum conservation. A method to obtain an exact probabilistic description of aggregation is presented. Since the one-dimensional gravitational attraction is confining, all particles will eventually form a single body. The detailed analysis of the probabilityP n (t) of such a complete merging before timet is performed for initial states ofn equidistant identical particles with uncorrelated velocities. It is found that for a macroscopic amount of matter (n→∞), this probability vanishes before a characteristic timet*. In the limit of a continuous initial mass distribution the exact analytic form ofP n (t) is derived. The analysis of collisions leading to the time-variation ofP n (t), reveals that in fact the merging into macroscopic bodies always occurs in the immediate vicinity oft*. Fort>t*, andn large,P n (t) describes events corresponding to the final aggregation of remaining microscopic fragments.

Temperature and dimension of nuclear tracks

From secondary ion mass and energy spectroscopy we can obtain information on the target properties and on track formation mechanisms. We present measurements of initial velocity and mass distributions of organic fragment ions desorbed from C, Al, and Au substrates by fast heavy atomic and molecular ion (e.g. 0.9 MeV N +/1.8 MeV N 2 +) bombardment. We show that molecular ions can be used to control the local and temporal distance of nuclear track formation processes. Information on the dimensions of infra- and ultratrack is obtained from a comparison between secondary ion emission from binary molecular and single incident ions.

Collisional Buildup of Molecular Clouds: Mass and Velocity Spectra

view Abstract Citations (10) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collisional Buildup of Molecular Clouds: Mass and Velocity Spectra Das, Mousumi ; Jog, Chanda J. Abstract We have studied the evolution of a local region of molecular clouds, moving in the mean gravitational potential of the Galactic disk. The clouds interact gravitationally with one another and undergo inelastic collisions. The clouds have been modeled as spheres, and a collision is assumed to take place when two clouds overlap. The outcome of a collision depends on the relative mass and velocity of the clouds and can result in the fragmentation or coalescence of the clouds. We find that the initial random mass distribution of the clouds evolves into a power-law distribution of the form N(m) ∝ mα, where α = -1.7 to -1.9, and is flatter toward the low-mass end. The mean one-dimensional random velocity of the molecular clouds is ∼8-10 km s-1 and is found to be independent of cloud mass. These results agree well with the observed mass and velocity distribution of molecular clouds. We also conclude that cloud collisions in a sheared galactic disk, rather than local gravitional interactions, are important in determining the mass and random velocity distribution of molecular clouds. Cloud collisions thus play a dominant role in the formation of molecular clouds. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177152 Bibcode: 1996ApJ...462..309D Keywords: ISM: CLOUDS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES full text sources ADS |

Mass-transshipment problems and ideal metrics

The Monge-Kantorovich mass-transshipment problem is to minimize the total cost ∫ R 2n c(x,y) db(x,y) over all transshipments b that satisfy the balancing condition b(●× R n)−b( R n×●)=(P−:Q)(●) ; P and Q are viewed as initial and final mass distributions, respectively, and c( x, y) is a cost function. The dual form of the problem was given by Kantorovich and Rubinstein (1958) for P and Q having bounded support, and the general case was considered in Lecture 20 of Dudley (1976). We extend these results studying more general transshipment problems based on higher-order differences. A new class of ideal metrics arises from our version of the Monge—Kantorovich problem, and a dual representation for these metrics is obtained.

The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

Nucleosynthesis in massive stars and the 12C(α, γ) 16O reaction rate

The evolution of a grid massive stars ranging from 12 to 40 M⊙ has been followed through all stages of nuclear burning up to the point of iron core collapse. The critical and highly uncertain rate for the reaction 12C(α, γ) 16O has been varied over a range from 0.5 to 3.0 times that given by Caughlan and Fowler and two different prescriptions for semiconvection have been explored. The nucleosynthesis resulting from integrating the yields of these models over plausible initial stellar mass distributions is found to be in excellent agreement with the observed solar abundances of virtually all the intermediate mass isotopes (16 ≤ A ≤ 32) if, and only if, the rate of the 12C(α, γ) 16O reaction is taken to be 1.7 ± 0.5 times that given by Caughlan and Fowler. This range is a small subset of what is allowed by current experimental measurements and can be taken as a nucleosynthetic “prediction” of the value that this rate needs to have in order to prevent 5- to 100-fold deviations from the observed relative abundances of key isotopes. These results are insensitive to the assumed slope of the initial stellar mass distribution within observational limits, and relatively insensitive to the theory of semiconvection (except for the apparent excessive production of 18O when semiconvective mixing is suppressed). Three of the stars have been followed through simulated explosions to obtain the explosive modifications to their nucleosynthesis (including the “neutrino process”), which for most isotopes is relatively small. Isotopic yields of both stable radioactive products are tabulated as are the calculated iron core masses of the presupernova stars.

Dissipationless galaxy formation revisited

A large set of numerical simulations has been performed by using two different N-body codes to derive detailed properties of the end-product of dissipationless collapse. Three classes of initial mass distribution have been adopted, characterized by different inhomogeneity scales, with velocity dispersion corresponding to a virial ratio in a range 5 × 10 −4 -0.2. The results show that the phase space properties of the final equilibrium state depend strongly on the initial mass distribution.

Evaporation rates of hot sodium clusters

A scheme based in density functional theory with pseudopotentials is used to obtain the normal modes of vibration of Nan clusters (4 ≤n ≤ 22). The monomer and dimer evaporation rates from thermally excited clusters are obtained in this harmonic approximation. The time evolution of the abundance spectra from an initial uniform mass distribution of hot clusters is studied and its influence in the experimentally observed spectra is discussed.

Mass transhipment problems and ideal metrics

Given initial and final mass distributions P and Q on we study dual and explicit solutions of the mass transhipment problem: Minimize subject to for all Borel where m n is a signed measure with d.f. having derivative For the usual choice of the cost function, the solution of the transhipment problem determines an ideal metric of order kn + 1.

Photometric evolution of galaxies in rich clusters: Numerical simulations

This paper briefly presents a numerical code which simulates the evolution of galaxies belonging to rich clusters. The evolutionary model considers both, cluster dynamics and galaxy photometry, taking into account the galaxy-cluster interactions (collisional stripping, merging and ram-pressure stripping by the ICM) and the intrinsic galaxy evolution. We use different initial mass distributions for galaxies and we briefly discuss the influence of the initial segregation in mass on the evolution of the photometrical properties.

A model for the formation of the Local Group

Observational tests of a model for the formation of the Local Group are presented and analyzed in which the mass concentration grows by gravitational accretion of local-pressure matter onto two seed masses in an otherwise homogeneous initial mass distribution. The evolution of the mass distribution is studied in an analytic approximation and a numerical computation. The initial seed mass and separation are adjusted to produce the observed present separation and relative velocity of the Andromeda Nebula and the Galaxy. If H(0) is adjusted to about 80 km/s/Mpc with density parameter Omega = 1, then the model gives a good fit to the motions of the outer members of the Local Group. The same model gives particle orbits at radius of about 100 kpc that reasonably approximate the observed distribution of redshifts of the Galactic satellites.