[en] We investigate the relation of the stellar initial mass function and the dense core mass function (CMF), using stellar masses and positions in 14 well-studied young groups. Initial column density maps are computed by replacing each star with a model initial core having the same star formation efficiency (SFE). For each group the SFE, core model, and observational resolution are varied to produce a realistic range of initial maps. A clump-finding algorithm parses each initial map into derived cores, derived core masses, and a derived CMF. The main result is that projected blending of initial cores causes derived cores to be too few and too massive. The number of derived cores is fewer than the number of initial cores by a mean factor of 1.4 in sparse groups and 5 in crowded groups. The mass at the peak of the derived CMF exceeds the mass at the peak of the initial CMF by a mean factor of 1.0 in sparse groups and 12.1 in crowded groups. These results imply that in crowded young groups and clusters, the mass distribution of observed cores may not reliably predict the mass distribution of protostars that will form in those cores.

[en] The activity and mass distribution of the summer daytime Taurid meteor complex stream Zeta Perseids and Beta Taurids in 1997-2004 is analysed and discussed. The results are based on radio observations obtained by the BLM forward-scatter system (Italy-Slovakia) and by the Ondrejov backscatter meteor radar (Czech Republic). The observed positions of maxima of the streams are in a general agreement with previous analysis. The observations indicate a filamentary structure of the streams, the existence of which is supported also by the mass exponent values

[en] We propose two-species catalysis-driven aggregation models in which coagulation of one species occurs only in the presence of another species (the catalyst). By means of generalized Smoluchovski rate equations, we study the kinetics of the system with the rate kernel K_A(i; j; l) ∝ l^υ, at which two A clusters of size i and j bond together under the catalytic action of a B cluster of size l. The results show that the cluster mass distribution of species A obeys a conventional scaling law in the υ ≥ 0 case while it may satisfy the modified scaling form in other cases. Moreover, it is found that the scaling exponents are nonuniversal and dependent on the value of index υ in most cases. On the other hand, we also investigate the scaling behaviour of the mutually catalysis-driven aggregate growth. For the system with the rate kernel K_A(i; j; l) ∝ l^υ₁ and K_B(i; j; l) ∝ l^υ₂, its kinetics depends crucially on the values of the indices υ₁ and υ₂. Either species scales according to the conventional or modified form in most cases; while the system may undergo a gelation transition in some special cases

[en] The authors describe a structure for launching the TE₀₁ and both polarizations of TE₁₂ modes into a highly overmoded low loss circular waveguide providing remote transmission for a multi-moded Delay Line Distribution System (DLDS). The power from four sources is delivered to four structure ports by rectangular waveguide, and the mode for each pulse subsection is selected by varying the relative phases of the sources. The four ports symmetrically feed a section of waveguide with a fourfold symmetric four-leaf clover-like (or quatrefoil) cross section, dimensioned so as to propagate only four TE modes, characterized as 0, π/2 (two polarizations), and π modes. The 0 and π/2 modes are well matched, the π mode only moderately so. A low loss taper transforms the initial cross section to a circular cross section; the 0 mode transforming to TE₀₁, the π/2 to TE₁₁, the π to TE₂₁, all with negligible mode conversion. A sausage type mode transducer then converts TE₁₁ to TE₁₂ (a lower loss mode), and the diameter is then expanded to the full ∼five inch diameter of the delay line. A separate structure to divert power from the last pulse subsection to the local group of accelerator structures is required

[en] The fragment mass distributions of platelike objects are investigated by conducting two types of experiments. The first is a open-quotes sandwich close-quote close-quote experiment in which thin glass and plaster plates are inserted between two larger stainless steel plates and an iron projectile is dropped onto the target plate at normal incidence. The second is a open-quotes lateral impact close-quote close-quote experiment in which a hypervelocity nylon projectile collides at the side of the plaster plates. There is a discrepancy in the power-law exponent of fragment mass distribution between the sandwich experiment and the lateral impact experiment. A model that agrees with the experimental results is proposed. copyright 1997 The American Physical Society

[en] In this paper, the question is dealt with what has prevented the formation of a strong bar in the majority of disc galaxies. No truly satisfactory answer has yet been given to this question and the difficulty remains a major obstacle to our understanding of the dynamics of these systems. In this review, the author discusses the implications of recent studies of this problem. (Auth./G.J.P.)

[en] The author discusses the formation of large-scale structures in the universe. He describes how filaments and disks may form from initial gravitational instabilities. Two fluctuations are considered: isothermal and adiabatic perturbations in a presupposed dark matter of neutrinos, gravitinos and photinos. Some problems left in this 'iho-spunge' model are listed. (Auth.)

[en] Primordial and episodic theories for the origin of comets are discussed. The implications of the former type for the origin of the solar system are considered. Candidate sites for the formation of comets are compared. The possible existence of a massive inner Oort cloud is discussed

[en] We present Herschel survey maps of the L 1641 molecular clouds in Orion A. We extracted both the filaments and dense cores in the region. We identified which of the dense sources are proto- or pre-stellar, and studied their association with the identified filaments. We find that although most (71%) of the pre-stellar sources are located on filaments there, is still a significant fraction of sources not associated with such structures. We find that these two populations (on and off the identified filaments) have distinctly different mass distributions. The mass distribution of the sources on the filaments is found to peak at 4 M _☉ and drives the shape of the core mass function (CMF) at higher masses, which we fit with a power law of the form dN/dlogM∝M ^–1.4±0.4. The mass distribution of the sources off the filaments, on the other hand, peaks at 0.8 M _☉ and leads to a flattening of the CMF at masses lower than ∼4 M _☉. We postulate that this difference between the mass distributions is due to the higher proportion of gas that is available in the filaments, rather than in the diffuse cloud

[en] Observations from the Galactic Arecibo L-band Feed Array H I (GALFA-H I) Survey of the tail of Complex C are presented and the halo clouds associated with this complex are cataloged. The properties of the Complex C clouds are compared to clouds cataloged at the tail of the Magellanic Stream to provide insight into the origin and destruction mechanism of Complex C. Magellanic Stream and Complex C clouds show similarities in their mass distributions (slope = -0.7 and -0.6 log (N( log (mass)))/ log (mass), respectively) and have a common line width of 20-30 km s^-1 (indicative of a warm component), which may indicate a common origin and/or physical process breaking down the clouds. The clouds cataloged at the tail of Complex C extend over a mass range of 10^1.1-10^4.8 M_sun, sizes of 10^1.2-10^2.6 pc, and have a median volume density and pressure of 0.065 cm^-3 and (P/k) = 580 K cm^-3. We do not see a prominent two-phase structure in Complex C, possibly due to its low metallicity and inefficient cooling compared to other halo clouds. Assuming that the Complex C clouds are in pressure equilibrium with a hot halo medium, we find a median halo density of 5.8 x 10^-4 cm^-3, which given a constant distance of 10 kpc is at a z-height of ∼3 kpc. Using the same argument for the Stream results in a median halo density of 8.4 x 10-⁵ (60 kpc/d) cm^-3. These densities are consistent with previous observational constraints and cosmological simulations. We also assess the derived cloud and halo properties with three-dimensional grid simulations of halo H I clouds and find that the temperature is generally consistent within a factor of 1.5 and the volume densities, pressures, and halo densities are consistent within a factor of three.