Observed Mass Distribution Research Articles

Search for Pair Production of a Newb′Quark that Decays into aZBoson and a Bottom Quark with the ATLAS Detector

A search is reported for the pair production of a new quark b' with at least one b' decaying to a Z boson and a bottom quark. The data, corresponding to 2.0 fb(-1) of integrated luminosity, were collected from pp collisions at √s = 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. Using events with a b-tagged jet and a Z boson reconstructed from opposite-charge electrons, the mass distribution of large transverse momentum b' candidates is tested for an enhancement. No evidence for a b' signal is detected in the observed mass distribution, resulting in the exclusion at a 95% confidence level of b' quarks with masses m (b') < 400 GeV that decay entirely via b' → Z+b. In the case of a vectorlike singlet b' mixing solely with the third standard model generation, masses m(b') < 358 GeV are excluded.

The dynamics of the bulge dominated galaxy NGC 7814 in MOND

The bulge dominated galaxy NGC 7814 provides one of the strongest dynamical tests possible for Modified Newtonian Dynamics (MOND). Spitzer 3.6 micron photometry fixes the bulge parameterisation and strongly constrains the properties of the sub-dominant stellar disk. Furthermore, the distance is known to better than 5 percent, virtually eliminating it as a free parameter. The rotation curve is easily measured, since the H I (and stellar) disks are edge on, and both the receding and approaching sides agree very well. In this paper we explore the agreement between the model and observed rotation curves in MOND given that the only two free parameters available are the mass-to-light ratios of the bulge and disk. We use a grid based MOND Poisson solver that accurately solves for the MOND gravity and produces our model rotation curves from a given mass distribution. The input to the Poisson solver is a 3D distribution of N particles which is generated from modelling the observed distribution of stars and gas in the galaxy. By ensuring a superior fit to the radial surface brightness profile than previous works, by virtue of a double Sersic fit to the bulge, we were able to produce excellent fits to the rotation curve with typical values for both mass-to-light ratios. We conclude that the model rotation curve of a mass distribution in MOND is extremely sensitive to the bulge-disk decomposition and even slight deviation from the observed mass distribution can produce large differences in the model rotation curve.

Motion of myosin head domains during activation and force development in skeletal muscle

Muscle contraction is driven by a change in the structure of the head domain of myosin, the "working stroke" that pulls the actin filaments toward the midpoint of the myosin filaments. This movement of the myosin heads can be measured very precisely in intact muscle cells by X-ray interference, but until now this technique has not been applied to physiological activation and force generation following electrical stimulation of muscle cells. By using this approach, we show that the long axes of the myosin head domains are roughly parallel to the filaments in resting muscle, with their center of mass offset by approximately 7 nm from the C terminus of the head domain. The observed mass distribution matches that seen in electron micrographs of isolated myosin filaments in which the heads are folded back toward the filament midpoint. Following electrical stimulation, the heads move by approximately 10 nm away from the filament midpoint, in the opposite direction to the working stroke. The time course of this motion matches that of force generation, but is slower than the other structural changes in the myosin filaments on activation, including the loss of helical and axial order of the myosin heads and the change in periodicity of the filament backbone. The rate of force development is limited by that of attachment of myosin heads to actin in a conformation that is the same as that during steady-state isometric contraction; force generation in the actin-attached head is fast compared with the attachment step.

Age distribution of the central stars of galactic disk planetary nebulae

The determination of ages of central stars of planetary nebulae (CSPN) is a complex problem, and there is presently no single method that can be generally applied. We have developed several methods to estimate the ages of CSPN, based both on the observed nebular properties and in some properties of the stars themselves.Our aim is to estimate the ages and the age distribution of CSPN and to compare the derived results with mass and age determinations of CSPN and white dwarfs based on empirical determinations of these quantities. We discuss several methods to derive the age distribution of CSPN, namely, (i) the use of an age-metallicity relation that also depends on the galactocentric distance, (ii) the use of an age-metallicity relation obtained for the galactic disk, and (iii) the determination of ages from the central star masses obtained from the observed nitrogen abundances. We consider a sample of planetary nebulae in the galactic disk, most of which ($\sim$ 69%) are located in the solar neighbourhood, within 3 kpc from the Sun. We estimate the age distribution of CSPN with average uncertainties of 1-2 Gyr, and compare our results with the expected distribution based both on the observed mass distribution of white dwarfs and on the age distribution derived from available mass distributions of CSPN. We conclude most CSPN in the galactic disk have ages under 6 Gyr, and that the age distribution is peaked around 2-4 Gyr.

Search for Higgs Bosons Predicted in Two-Higgs-Doublet Models via Decays to Tau Lepton Pairs in 1.96 TeVpp¯Collisions

We present the results of a search for Higgs bosons predicted in two-Higgs-doublet models, in the case where the Higgs bosons decay to tau lepton pairs, using 1.8 fb(-1) of integrated luminosity of pp collisions recorded by the CDF II experiment at the Fermilab Tevatron. Studying the mass distribution in events where one or both tau leptons decay leptonically, no evidence for a Higgs boson signal is observed. The result is used to infer exclusion limits in the two-dimensional space of tanbeta versus m(A) (the ratio of the vacuum expectation values of the two Higgs doublets and the mass of the pseudoscalar boson, respectively).

Einstein’s Theory of Gravity and the Problem of Missing Mass

The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton's and Einstein's theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein's theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter.

Non-circular motions and the cusp-core discrepancy in dwarf galaxies

Context. The cusp-core discrepancy is one of the major problems in astrophysics. It results from comparing the observed mass distribution of galaxies with the predictions of Cold Dark Matter simulations. The latter predict a cuspy density profile in the inner parts of galaxies, whereas observations of dwarf and low surface brightness galaxies show a constant density core. Aims. We want to determine the shape of the dark matter potential in the nuclear regions of a sample of six nearby irregular dwarf galaxies. Methods. In order to quantify the amount of non-circular motions which could potentially affect a mass decomposition, we first perform a harmonic decomposition of the HI Hermite velocity fields of all sample galaxies. We then decompose the HI rotation curves into different mass components by fitting NFW and pseudo-isothermal halo models to the HI rotation curves using a chi^2 minimisation. We model the minimum-disc, the minimum-disc+gas, and the maximum-disc cases. Results. The non-circular motions are in all cases studied here of the order of only a few km/s (generally corresponding to less than 25% of the local rotation velocity), which means that they do not significantly affect the rotation curves. The observed rotation curves can better be described by the cored pseudo-isothermal halo than by the NFW halo. The slopes of the dark matter density profiles confirm this result and are in good agreement with previous studies. The quality of the fits can often be improved when including the baryons, which suggests that they contribute significantly to the inner part of the density profile of dwarf galaxies.

An Interpretation of the Anomalously Low Mass of Mars

Conventionally the models of the solar nebula have been constructed so that the surface density of the nebula is a monotonic function of the heliocentric distance. This mass distribution is not consistent with the observed mass distribution of planets, in particular, the Mars drop (the anomalously low mass of Mars). In order to explain this Mars drop, some researchers adopt processes to take mass out of the Mars region, and the approach taken so far is from the point of view of planetary formation theory. Here we present our new calculations of the evolution of the solar nebula. We find that the surface density in the nebula is not monotonic and that there is a minimum in the Mars region. This naturally fits the planet mass distribution, especially the Mars drop. We suggest that the existence of this minimum leads to the low mass of Mars in the following three ways. (1) The low surface density of the Mars region gives a low mass supply, and (2) it gives a low rate of planetesimal formation from dust. (3) The low surface density in the Mars region preferentially makes Mars a leftover protoplanet without gaining much mass during chaotic growth, the last stage of planet formation.

Dynamical evolution of galaxy clusters in the framework of the N-body problem. The formation of supermassive cD galaxies

We have carried out numerical simulations of the dynamical evolution of galaxy clusters taking into account merging when the relative velocities of the colliding galaxies are low. In particular, we study the evolution of the structure, mass spectrum, and velocity spectrum of a cluster of a thousand galaxies, as well as the growth of the central supermassive cD galaxy. The initial velocity dispersion of the galaxies and the rotation of the cluster were taken into account. The observed logarithmic spectrum dN ∼ % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC% vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbuLwBLnhiov2DGi1BTfMBaeHb% d9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb% L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe% pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaadeWaaq% aadaqbaaGcbaWaaSqaaSqaaiabdsgaKjabd2eanbqaaiabd2eanbaa% aaa!3E82! $$\tfrac{{dM}}{M}$$ was adopted as the initial mass spectrum. The dynamical evolution of galaxy clusters, allowing for the possible merging of colliding galaxies, results in the emergence of a central supermassive galaxy, whose mass continuously increases due to mergers. This occurs only if the mass of the central galaxy becomes greater than ∼0.1 of the total mass of the cluster. The observation of cD galaxies with relative masses of ∼0.01 suggests that they initially formed in the cluster core, merged with nearby galaxies, and accreted intergalactic gas. The model indicates that a logarithmic galaxy mass spectrum is preserved during the cluster evolution, despite the substantial decrease in the number of galaxies in the cluster with time. The model can also reproduce the observed mass distribution with distance from the cluster center, M r ∼ r 1.7.

The Hyades stream: an evaporated cluster or an intrusion from the inner disk?

The nature of the Hyades stream, or Hyades moving group, is a long-standing question of Galactic Astronomy. While it has become widely recognized that the Hercules stream, an unbound group of stars lagging behind galactic rotation and moving outward in the galactic disk, is associated with the outer Lindblad resonance of the rotating galactic bar, there is still some debate about the nature of the more prominent low-velocity stream sharing the kinematics of the Hyades open cluster. Is this stream caused by additional non-axisymmetric perturbations of the galactic potential, such as transient or quasi-stationary spiral waves, or by the on-going evaporation of the Hyades cluster? Here, a simple observational test has been designed to determine whether the Hyades stream is primarily composed of coeval stars originating from the Hyades cluster, or of field stars. Using the Geneva-Copenhagen survey of F and G dwarfs, we compare the mass distribution and metallicity of the stream to those of field disk stars. If the Hyades stream is composed of stars trapped at resonance, its mass distribution should obey the present-day mass function (PDMF) of the disk, and its metallicity should reflect its origin in the inner regions of the Galaxy. On the other hand, if it is an evaporated cluster, we expect a different mass distribution, depending on the inital mass function (IMF) of the cluster, and on the proportion of evaporated stars as a function of mass. We find that extreme conditions have to be adopted for the selective evaporation and IMF of the cluster to make the observed mass distribution of the stream only roughly consistent (at a one-sigma level) with the coeval evaporated cluster scenario. The observed mass distribution is in much better agreement with the PDMF of the field. The peculiar metallicity of the stream is inconsistent with that of a field population from the solar neighbourhood trapped in the primordial cluster during its formation process and subsequently evaporated. These observations thus favour a resonant origin for the Hyades stream.

Aerosol chemical and optical properties over the Paris area within ESQUIF project

Abstract. Aerosol chemical and optical properties are extensively investigated for the first time over the Paris Basin in July 2000 within the ESQUIF project. The measurement campaign offers an exceptional framework to evaluate the performances of the chemistry-transport model CHIMERE in simulating concentrations of gaseous and aerosol pollutants, as well as the aerosol-size distribution and composition in polluted urban environments against ground-based and airborne measurements. A detailed comparison of measured and simulated variables during the second half of July with particular focus on 19 and 31 pollution episodes reveals an overall good agreement for gas-species and aerosol components both at the ground level and along flight trajectories, and the absence of systematic biases in simulated meteorological variables such as wind speed, relative humidity and boundary layer height as computed by the MM5 model. A good consistency in ozone and NO concentrations demonstrates the ability of the model to reproduce the plume structure and location fairly well both on 19 and 31 July, despite an underestimation of the amplitude of ozone concentrations on 31 July. The spatial and vertical aerosol distributions are also examined by comparing simulated and observed lidar vertical profiles along flight trajectories on 31 July and confirm the model capacity to simulate the plume characteristics. The comparison of observed and modeled aerosol components in the southwest suburb of Paris during the second half of July indicates that the aerosol composition is rather correctly reproduced, although the total aerosol mass is underestimated by about 20%. The simulated Parisian aerosol is dominated by primary particulate matter that accounts for anthropogenic and biogenic primary particles (40%), and inorganic aerosol fraction (40%) including nitrate (8%), sulfate (22%) and ammonium (10%). The secondary organic aerosols (SOA) represent 12% of the total aerosol mass, while the mineral dust accounts for 8%. The comparison demonstrates the absence of systematic errors in the simulated sulfate, ammonium and nitrates total concentrations. However, for nitrates the observed partition between fine and coarse mode is not reproduced. In CHIMERE there is a clear lack of coarse-mode nitrates. This calls for additional parameterizations in order to account for the heterogeneous formation of nitrate onto dust particles. Larger discrepancies are obtained for the secondary organic aerosols due to both inconsistencies in the SOA formation processes in the model leading to an underestimation of their mass and large uncertainties in the determination of the measured aerosol organic fraction. The observed mass distribution of aerosols is not well reproduced, although no clear explanation can be given.

The open-cluster initial--final mass relationship and the high-mass tail of the white dwarf distribution

Recent studies of white dwarfs in open clusters have provided new constraints on the initial - final mass relationship (IFMR) for main sequence stars with masses in the range 2.5 - 6.5 Mo. We re-evaluate the ensemble of data that determines the IFMR and argue that the IFMR can be characterised by a mean initial-final mass relationship about which there is an intrinsic scatter. We investigate the consequences of the IFMR for the observed mass distribution of field white dwarfs using population synthesis calculations. We show that while a linear IFMR predicts a mass distribution that is in reasonable agreement with the recent results from the PG survey, the data are better fitted by an IFMR with some curvature. Our calculations indicate that a significant (~28%) percentage of white dwarfs originating from single star evolution have masses in excess of ~0.8 Mo, obviating the necessity for postulating the existence of a dominant population of high-mass white dwarfs that arise from binary star mergers.

The relation between the observed mass distribution for compact stars and the mechanism for supernova explosions

The observed mass distribution for the compact remnants of massive stars (neutron stars and black holes) and its relationship to the possible mechanism of ejection of the envelopes of type II and Ib/c supernovae are analyzed. The observed lack of compact remnants with masses 1.5–3 M⊙ suggests a magneto-rotational mechanism for the supernovae, and a soft equation of state for neutron stars with limiting masses near 1.5 M⊙. The observational consequences of this hypothesis are discussed.

Two Substellar Companions Orbiting HD 168443

Precise Doppler measurements during 4.4 yr from the Keck/HIRES spectrometer reveal two superimposed Keplerian velocity variations for HD 168443 (G6 IV). A simultaneous orbital fit to both companions yields companion masses of M sin i = 7.7 and 17.2 MJUP, orbital periods of P = 58 days and 4.8 yr, semimajor axes of a = 0.29 and 2.9 AU, and eccentricities of e = 0.53 and 0.20. An upper limit to the mass of the outer companion of 42 MJUP is derived from the lack of astrometric wobble. The outer companion was not detected with Keck adaptive optics in the near-IR. Dynamical simulations show that the system is remarkably stable for all possible masses of both companions. The two orbiting companions have masses that are probably near and slightly above the upper end of the observed mass distribution of planets at 10 MJUP. Formation in a protoplanetary disk seems plausible. But these objects present a puzzle about their formation and dynamical history, as well as about their possible kinship with planetary systems and triple-star systems.

A dual‐domain mass transfer approach for modeling solute transport in heterogeneous aquifers: Application to the Macrodispersion Experiment (MADE) site

A large‐scale natural‐gradient tracer test in a highly heterogeneous aquifer at the Macrodispersion Experiment (MADE) site on the Columbus Air Force Base in Mississippi is simulated using three‐dimensional hydraulic conductivity distributions derived from borehole flowmeter test data. Two methods of hydraulic conduct(fBm), are used to construct the hydraulic conductivity distributions needed by the numerical model. Calculated and observed mass distributions are compared to evaluate the effectiveness of the dual‐domain mass transfer approach relative to the single‐domain advection‐dispersion approach. The results show that the classical Fickian advection‐dispersion model can reproduce reasonably well the observed tritium plume above a certain concentration limit but fails to reproduce the extensive spreading of the tracer at diluted concentrations as observed in the field. The alternative dual‐domain mass transfer model is able to represent the rapid, anomalous spreading significantly better while retaining high concentrations near the injection point. This study demonstrates that the dual‐domain mass transfer approach may offer a practical solution to modeling solute transport in highly heterogeneous aquifers where small‐scale preferential flow pathways cannot be fully and explicitly represented by the spatial discretization of the numerical model.

Chaos and fractals in geodesic motions around a nonrotating black hole with halos

We study the escape dynamics of test particles in general-relativistic gravitational fields generated by core-shell models, which are used in astrophysics as idealized models to observed mass distributions, such as the interior of galaxies. As a general-relativistic core-halo system, we use exact axisymmetric static solutions of Einstein's field equations which represent the superposition of a central Schwarzschild black hole (the core) and multipolar fields from external masses (the halo). We are particularly interested in the occurrence of chaos in the escape, which is characterized by a great sensitivity of the choice of escape by a test particle to initial conditions. The motion of both material particles and zero rest mass particles is considered. Chaos is quantified by the fractal dimension of the boundary between the basins of the different escapes. We find chaos in the motion of both material particles and null geodesics, but its intensity depends strongly on the halo. We have found for all the cases we have considered that massless particles are less chaotic than massive particles.

DISTRIBUTION OF MATTER IN THE SOLAR SYSTEM

A new formula for the distribution of matter in the solar system is derived by assuming that the planets were formed from trapped particles of a cosmic dust disk attached to the Sun. Contrary to Boltzmann's distribution which predicts thermal collapse of this cloud on the Sun, it is found that if the primeval particles move on circular orbits according to Kepler's law, then their velocities obey a 2-D global Maxwellian and their distribution in space is given by p0 (r)=(α r2)\exp(-α r) (Km-1); α = 888.73 × 106 Km. The form ofp0 (r) agrees with the observed mass distribution of the planets and explains their present large angular momentum. PACS numbers: 96.35.Cp, 96.35.Fs

Observed mass distribution of spontaneous fission fragments from samples of lime—an SSNTD study

SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements.

The Mass Distribution of Stellar Black Holes

We examine the distribution of masses of black holes in transient low mass X-ray binary systems. A Bayesian analysis suggests that it is probable that six of the seven systems with measured mass functions have black hole masses clustered near seven solar masses. There appears to be a significant gap between the masses of these systems and those of the observed neutron stars. The remaining source, V404 Cyg, has a mass significantly larger than the others, and our analysis suggests that it is probably drawn from a different distribution. Selection effects do not appear to play a role in producing the observed mass distribution, which may be explained by currently unknown details of the supernova explosions and of binary evolution prior to the supernova.

Dynamics of the Leonid Meteoroid Stream: a Numerical Approach

AbstractWe have simulated the evolution of the Leonid stream via numerical integration of 3 million test particles ejected from 55P/Tempel-Tuttle during five perihelion passages of that comet. Using the Whipple ejection velocity formula and a random ejection spread in true anomaly about the parent comet orbit inside 2.3 AU, we have followed the subsequent evolution of Leonid meteoroids differing by over 5 orders of magnitude in mass under the influence of radiation pressure and planetary perturbations. By comparing the model predictions of Leonid activity on a year by year basis with the available observations we have attempted to determine roughly the time of ejection associated with each Leonid storm occurrence and model the observed mass distribution. On the basis of the demonstrated accuracy of the model we make predictions regarding times of peak activity and relative strengths for the Leonid returns for each year during the latter part of the 1990s.