Dense Central Core Research Articles

Visualizing the Attack of RNase Enzymes on Dendriplexes and Naked RNA Using Atomic Force Microscopy

Cationic polymers such as poly(amidoamine), PAMAM, dendrimers have been used to electrostatically complex siRNA molecules forming dendriplexes for enhancing the cytoplasmic delivery of the encapsulated cargo. However, excess PAMAM dendrimers is typically used to protect the loaded siRNA against enzymatic attack, which results in systemic toxicity that hinders the in vivo use of these particles. In this paper, we evaluate the ability of G4 (flexible) and G5 (rigid) dendrimers to complex model siRNA molecules at low +/− ratio of 2/1 upon incubation for 20 minutes and 24 hours. We examine the ability of the formed G4 and G5 dendriplexes to shield the loaded siRNA molecules and protect them from degradation by RNase V1 enzymes using atomic force microscopy (AFM). Results show that G4 and G5 dendrimers form similar hexagonal complexes upon incubation with siRNA molecules for 20 minutes with average full width of 43±19.3 nm and 62±8.3 at half the maximum height, respectively. AFM images show that these G4 and G5 dendriplexes were attacked by RNase V1 enzyme leading to degradation of the exposed RNA molecules that increased with the increase in incubation time. In comparison, incubating G4 and G5 dendrimers with siRNA for 24 hours led to the formation of large particles with average full width of 263±60 nm and 48.3±2.5 nm at half the maximum height, respectively. Both G4 and G5 dendriplexes had a dense central core that proved to shield the loaded RNA molecules from enzymatic attack for up to 60 minutes. These results show the feasibility of formulating G4 and G5 dendriplexes at a low N/P (+/−) ratio that can resist degradation by RNase enzymes, which reduces the risk of inducing non-specific toxicity when used in vivo.

Leaf Structure and Histochemical Investigation in Papaver rhoeas L. (Corn Poppy, Field Poppy)

The anatomy of the dorsiventral, amphistomatic leaf of Papaver rhoeas was investigated. It was a simple structure possessing large epidermal cells having their vacuole impregnated with glycoproteins which varied in texture, forming a dense, hard core in the middle of the vacuole. Slender rays of cisternae radiated from the dense central core to the cell wall. Thin-walled palisade cells presented a unique, lobed shape probably creating larger surfaces for gas exchange. Mesophyll cells secreted phenolics, condensed tannins, alkaloids, terpene containing steroids and sesquiterpenes. P. rhoeas although being a therophyte, has adopted some structural features common in mediterranean phanerophytes.

Silent Colonic Malakoplakia in a Living-Donor Kidney Transplant Recipient Diagnosed during Annual Medical Examination

Malakoplakia is a characteristic inflammatory condition, which is usually seen in the urogenital tract, and less frequently in the gastrointestinal tract. We present a case of colonic malakoplakia in an immunocompromised patient. A 55-year-old female visited the outpatient clinic for routine cancer surveillance. Her past medical history was significant for kidney transplantation 11 years ago, and she had been taking immunosuppressants. A colonoscopy revealed several depressed flat lesions and elevated polyps, which were 0.3 to 0.4 cm in size and accompanied by whitish exudates. A biopsy revealed an infiltration of histiocytes with ample granular eosinophilic cytoplasm, with some lymphocytes and plasma cells. Many histiocytes had the characteristic morphology, described as Michaelis-Gutmann bodies: one or several round basophilic structures of approximately 1 to 10 µm in size with some being laminated, some appearing homogeneous, and others having a dense central core with a targetoid appearance. These Michaelis-Gutmann bodies were positively stained on von Kossa stain, and were diagnostic for malakoplakia.

A mid-infrared imaging catalogue of post-asymptotic giant branch stars★

Post-AGB stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the Asymptotic Giant Branch (AGB) towards the Planetary Nebula stage. There is growing evidences that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of Post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of Post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VISIR/VLT, T-Recs/Gemini South and Michelle/Gemini North. We found that all the the Proto-Planetary Nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non resolved. The resolved targets can be divided in two categories. The nebulae with a dense central core, that are either bipolar and multipolar. The nebulae with no central core have an elliptical morphology.The dense central torus observed likely host binary systems which triggered fast outflows that shaped the nebulae.

H2flows in the Corona Australis cloud and their driving sources

We uncover the H2 flows in the Corona Australis molecular cloud and in particular identify the flows from the Coronet cluster. Near-infrared H2 v=1--0 S(1), 2.12micron-line, narrow-band imaging survey of the R CrA cloud core was carried out. We identify the best candidate-driving source for each outflow by comparing the flow properties, available proper motions, and the known/estimated properties of the driving sources. We also adopted the thumbrule of outflow power as proportional to source luminosity and inversely proportional to the source age to reach a consensus. Results: Continuum-subtracted, narrow-band images reveal several new Molecular Hydrogen emission-line Objects (MHOs). Together with previously known MHOs and Herbig-Haro objects we catalog at least 14 individual flow components of which 11 appear to be driven by the RCrA aggregate members. The flows originating in the Coronet cluster have lengths of ~0.1-0.2 pc. Eight out of nine submillimeter cores mapped in the Coronet cluster region display embedded stars driving an outflow component. Roughly 80% of the youngest objects in the Coronet are associated with outflows. The MHO flows to the west of the Coronet display lobes moving to the west and vice-versa, resulting in nondetections of the counter lobe in our deep imaging. We speculate that these counterflows may be experiencing a stunting effect in penetrating the dense central core. Conclusions:Although this work has reduced the ambiguities for many flows in the Coronet region, one of the brightest H2 feature (MHO2014) and a few fainter features in the region remain unassociated with a clear driving source. The flows from Coronet, therefore, continue to be interesting targets for future studies.

A mid-infrared imaging survey of post-AGB stars

AbstractPost-AGB stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the Asymptotic Giant Branch (AGB) towards the planetary nebula stage. There is growing evidences that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VISIR/VLT, T-Recs/Gemini South and Michelle/Gemini North. We found that all the the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non resolved. The resolved targets can be divided in two categories. The nebulae with a dense central core, that are either bipolar and multipolar. The nebulae with no central core have an elliptical morphology. The dense central torus observed likely host binary systems which triggered fast outflows that shaped the nebulae.

Jackstone: A rare entity of vesical calculus

Jackstone calculi are urinary tract stones that have a specific appearance resembling toy jacks. They are almost always composed of calcium oxalate dihydrate consist of a dense central core and radiating spicules. They are usually light brown with dark patches and are usually described to occur in the urinary bladder and rarely in the upper urinary tract. Their appearance on plain radiographs and computed tomography in human patients has been described.

A millimeter survey of ultra-compact HII-regions and associated molecular clouds

We report observations, using the IRAM 30 m telescope, of 30 ultracompact and hypercompact HII regions in the lines of HCO + (3−2) and/or HCO + (1−0) and H30α and/or H39α. Images are presented in both HCO + (3−2) and H30α toward a subset of regions (16 in HCO + (3−2), 14 in H30α) with a resolution of 12 �� . In addition, H 13 CO + (3−2) observations are reported toward 13 HII regions where HCO + (3−2) displays complex profiles. It is shown that the absorption dips in the HCO + profiles are due to HCO + self-absorption, not absorption of the HII free-free emission or warm dust emission surrounding the HII region or two velocity components along the line of sight. It was found that among the sources with self-absorbed profiles, 8 are contracting and 5 are expanding. Mass fluxes are found to be typically a few times 10 −3 Myr −1 , implying time scales for massive star formation <10 5 yrs. HCO + and H2 column densities are estimated for a subset of the sources from which masses of the dense central cloud cores were estimated. Implications of the derived column densities, masses, flow velocities, and mass fluxes are discussed. Ultra-compact (UC) HII regions are sites of recent massive star formation. UC HII regions are of special interest because they occupy an important stage in the evolution of young massive stars that is still only understood in broad outline. Identifying the ionizing star(s) and their associated natal cluster of lower mass stars in UC HII regions has proven quite difficult; identifi- cations have been reported for only a few UC HII regions. The immediate regions around the central star(s) of UC HII regions are expected to be very dynamic due to possible infall, outflows, stellar winds, accretion disk rotation, turbulence, and shocks. The dynamics and physical properties of the photo-dissociation regions (PDRs) that surround UC HII regions and the ambient natal molecular gas that surrounds the PDRs must also be in- cluded to place UC HII regions in context with their environ- ments. Spectroscopy of the H + ,P DR(H 0 ), and molecular en- velopes (H2) is essential to understand the interactions of UC HII regions with their environments. Churchwell (2002) has ar- gued, based on the lack of evidence for outflows in high reso- lution radio continuum images, that by the time young massive stars have formed UC HII regions they have largely ceased the accretion process. This is indirect evidence that has so far not been confirmed by spectroscopic observations. To understand the early evolution of massive stars and how they impact their environments, we must determine at what evolutionary stage young massive stars quench accretion and by what mechanism. Is it because the stars use all the matter in their neighborhood or

Adenovirus Virion Stability and the Viral Genome: Size Matters

Ongoing investigations into the fundamental aspects of virus biology continue to provide crucial insights for the development of more effective virus-based therapeutics. Within the field of gene therapy, these discoveries have translated into virus vectors with improved tissue tropism, prolonged transgene expression, and enhanced safety. However, radical modifications to the viral genome or capsid constituents can have marked effects on virion stability. In particular, recent insights into the role of viral genomes in contributing to the physical stability of the virion highlight the need to reconsider this heretofore underappreciated aspect of vector design. Here we discuss the impact of the genome on virion stability, with particular emphasis on the development of adenovirus (Ad)-based vectors.

BIMA N2H+1-0 MAPPING OBSERVATIONS OF L183: FRAGMENTATION AND SPIN-UP IN A COLLAPSING, MAGNETIZED, ROTATING, PRESTELLAR CORE

We have used the Berkeley-Illinois-Maryland Array to make deep N2H+ 1-0 maps of the prestellar core L183, in order to study the spatial and kinematic substructure within the densest part of the core. Three spatially and kinematically distinct clumps are detected, which we label L183-N1, L183-N2, and L183-N3. L183-N2 is approximately coincident with the submillimeter dust peak and lies at the systemic velocity of L183. Thus we conclude that L183-N2 is the central dense core of L183. L183-N1 and 3 are newly discovered fragments of L183, which are marked by velocity gradients that are parallel to, but far stronger than, the velocity gradient of L183 as a whole, as detected in previous single-dish data. Furthermore, the ratio of the large-scale and small-scale velocity gradients, and the ratio of their respective size-scales, are consistent with the conservation of angular momentum for a rotating, collapsing core undergoing spin-up. The inferred axis of rotation is parallel to the magnetic field direction, which is offset from its long axis, as we have seen in other prestellar cores. Therefore, we propose that we have detected a fragmenting, collapsing, filamentary, prestellar core, rotating about its B-field, which is spinning up as it collapses. It will presumably go on to form a multiple protostellar system.

Evolution of the electrically exploding wire observed with a Mach–Zehnder interferometer

The evolution of an exploding titanium wire embedded in 10 kPa air was studied with Mach–Zehnder interferometry. The exploding wire is characterized by a central dense core as well as the surrounding plasma and a rapidly expanding gas shell. Based on the fringe shifts, the electron density of the plasma and the increased density in the gas shell were calculated to be about 1.94×1018/cm3 and 4.78×10−4 g/cm3, respectively. The expanding speed of the gas shell is about 2.28 km/s. A thermal expansion lag of the dense vapor core and two-phase vaporization of the wire were observed. Due to the wire exploding in “under heat” mode, the first phase of the vaporization is by the Joule heating and the second one by the plasma heating.

EFFECT OF CENTRAL MASS CONCENTRATION ON THE FORMATION OF NUCLEAR SPIRALS IN BARRED GALAXIES

We have performed smoothed particle hydrodynamics simulations to study the response of the central kiloparsec region of a gaseous disk to the imposition of nonaxisymmetric bar potentials. The model galaxies are composed of three axisymmetric components (halo, disk, and bulge) and a nonaxisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. The potential of spherical γ-models of Dehnen is adopted for the bulge component whose density varies as r−γ near the center and r−4 at larger radii and, hence, possesses a central density core for γ = 0 and cusps for γ>0. Since the central mass concentration of the model galaxies increases with the cusp parameter γ, we have examined here the effect of the central mass concentration by varying the cusp parameter γ on the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies. Our simulations show that the symmetric two-armed nuclear spirals are formed by hydrodynamic spiral shocks driven by the gravitational torque of the bar for the models with γ = 0 and 0.5. On the other hand, the symmetric two-armed nuclear spirals in the models with γ = 1 and 1.5 are explained by gas density waves. Thus, we conclude that the mechanism responsible for the formation of symmetric two-armed nuclear spirals in barred galaxies changes from hydrodynamic shocks to gas density waves as the central mass concentration increases from γ = 0 to 1.5.

HIGH-RESOLUTION ROTATION CURVES AND GALAXY MASS MODELS FROM THINGS

We present rotation curves of 19 galaxies from THINGS, The HI Nearby Galaxy Survey. The high spatial and velocity resolution of THINGS make these the highest quality HI rotation curves available to date for a large sample of nearby galaxies, spanning a wide range of HI masses and luminosities. The high quality of the data allows us to derive the geometrical and dynamical parameters using HI data alone. We do not find any declining rotation curves unambiguously associated with a cut-off in the mass distribution out to the last measured point. The rotation curves are combined with 3.6 um data from SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models. Our best-fit, dynamical disk masses, derived from the rotation curves, are in good agreement with photometric disk masses derived from the 3.6 um images in combination with stellar population synthesis arguments and two different assumptions for the stellar Initial Mass Function (IMF). We test the Cold Dark Matter-motivated cusp model, and the observationally motivated central density core model and find that (independent of IMF) for massive, disk-dominated galaxies, all halo models fit apparently equally well; for low-mass galaxies, however, a core-dominated halo is clearly preferred over a cuspy halo. The empirically derived densities of the dark matter halos of the late-type galaxies in our sample are half of what is predicted by CDM simulations, again independent of the assumed IMF.

Membrane Transformations in Degenerating Rodlet Cells in Fishes of Two Teleostean Families (Salmonidae, Cyprinidae)

Rodlet cells (RCs) of teleosts are identified by their fibrillar capsule and peculiar inclusions, the rodlets, consisting of a club-like sac and a central dense core. Former ultrastructural studies showing signs of hypertrophy of endoplasmic reticulum (ER) were followed up in Salmonids (Oncorhynchus mykiss, Salmo trutta L.) and compared with Cyprinids (Cyprinus carpio L., Carassius auratus L., Alburnus alburnus). Focusing on membrane transformations, unusual undulations of the membranes of rodlet sacs and often apposed ER-membranes, which were observed in mature or discharging cells, increased continuously in degenerating stages and ejected cytoplasmic packages or rodlets. Tubular elements (ø 25-30 nm or 30-50 nm) or small vesicles appeared partly derived from them. Terminal stages of this development were represented by RCs retained in the epithelium, which were completely filled by stacks of tubules and cores. Convoluted membranes were also found persisting between mostly undissolved rodlets at the epithelial surfaces. In Cyprinid species, the membrane changes were less conspicuous but essentially similar, including stages with confluent ER reported only in trout up to now. The membrane transformations resemble structures known as "crystalloid ER" indicating a disturbance in the protein production. The positive immunocytochemical reaction for calreticulin in the rodlet sacs, a luminal ER chaperone mediating recycling of misfolded proteins and upregulated during stress, supports this interpretation. The ER stress-reaction is an evolutionary conservative cytoprotective mechanism during physiological, environmental, and genetic aberrations and fits the increase of RCs reported in quite different situations, although details of its triggering need further investigation.

Von Hansemann cells and Michaelis-Gutmann bodies in a retroperitoneal mass.

A 22-year-old woman was hospitalized for progressive right lumbar pain and tumefaction, fever and malaise of several months’ duration. The patient had a 12-year history of intermittent symptoms of urinary tract infections. An exhaustive study searching for a cause of the recurrent infections was not done. Her family history was negative for renal diseases. On examination there was tenderness, redness and a fistulous tract in the right lumbar region. Laboratory investigations showed a normal renal function. Urinalysis revealed numerous leukocytes. An abdominal computed tomography scan revealed a right kidney displaced and compressed by a well-defined lesion with cystic aspect that is in contact with renal pelvis. Adjacent there was an ill-defined retroperitoneal mass which was in contact with the psoas, extending from the diaphragm to the pelvis, with involvement of the lumbar subcutaneous tissue and connecting to the fistulous tract (Figure ​(Figure1).1). Left kidney appeared normal. A CT-guided percutaneous biopsy of the mass was undertaken. Fig. 1 CT scan revealed a well-defined capsulated mass with cystic aspect in contact with the right renal pelvis. In retroperitoneum there is an ill-defined mass in contact with the psoas and extending to paravertebral space, lumbar subcutaneous tissue and skin ... The biopsy revealed clusters of histiocytes with ample granular eosinophilic cytoplasm. In many of them were one or more round basophilic structures measuring between 1 μm and 10 μm approximately 1 μm and 10 μm; some were laminated, others appeared homogeneous, and others had a dense central core with a targetoid appearance (Figure ​(Figure2).2). Nephrectomy of the right kidney demonstrated focal congenital cystic renal dysplasia. Fig. 2 Collections of large histiocytes with granular eosinophilic cytoplasm: von Hansemann cells. The cytoplasm contains abundant basophilic inclusions with a variable size: Michaelis–Gutmann bodies. Some of them are laminated and others have targetoid ... Malakoplakia is a chronic inflammatory process which most often affects the urinary tract, but it may involve a variety of other organs. Malakoplakia is the result of an acquired defect in macrophage function causing impairment of bactericidal activity. The large macrophages that are present at sites of infection (von Hansemann cells) exhibit numerous secondary lysosomes containing partially digested organisms. Fusion and calcification of these lysosomes result in the formation of intracytoplasmic bodies called Michaelis–Gutmann bodies, considered pathognomonic of malakoplakia [1,2]. Conflict of interest statement. None declared.

The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess

We analyze brightness profiles for 143 early-type galaxies in the Virgo and Fornax Clusters, observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Sérsic models are found to provide accurate representations of the global profiles with a notable exception: the observed profiles deviate systematically inside a characteristic "break" radius of Rb ≈ 0.02−0.01+0.025Re, where Re is the effective radius of the galaxy. The sense of the deviation is such that bright galaxies (MB ≲ − 20) typically show central light deficits with respect to the inward extrapolation of the Sérsic model, while the great majority of low- and intermediate-luminosity galaxies (-19.5 ≲ MB ≲ − 15) show central light excesses; galaxies of intermediate luminosities (-20≲ MB ≲ − 19.5) are generally well fitted by Sérsic models over all radii. We show that the slope, γ', of the central surface brightness profiles, when measured at fixed fractions of Re, varies smoothly as a function of galaxy luminosity in a manner that depends sensitively on the choice of measurement radius. We find no evidence for a core/power-law dichotomy, and show that a recent claim of strong bimodality in γ' is likely an artifact of the biased galaxy selection function used in that study. To provide a more robust characterization of the inner regions of galaxies, we introduce a parameter Δ0.02 = log (g/ S) —where g and S are the integrated luminosities inside 0.02Re of the observed profile and of the inward extrapolation of the outer Sérsic model—to describe the central luminosity deficit (Δ0.02 < 0) or excess (Δ0.02 > 0). We find that Δ0.02 varies smoothly over the range of ≈720 in luminosity spanned by the sample galaxies, with again no evidence for a dichotomy. We argue that the central light excesses in MB ≳ − 19 galaxies may be the analogs of the dense central cores predicted by some numerical simulations to form via gas inflows.

Self-consistent triaxial de Zeeuw-Carollo models

We use the standard method of Schwarzschild to construct self-consistent solutions for the triaxial de Zeeuw & Carollo (1996) models with central density cusps. ZC96 models are triaxial generalizations of spherical γ-models ofDehnen whose densities vary as r -γ near the center and r -4 at large radii and hence, possess a central density core for γ = 0 and cusps for γ > 0. We consider four triaxial models from ZC96, two prolate triaxials: (p, q) = (0.65,0.60) with y = 1.0 and 1.5, and two oblate triaxials: (p, q) = (0.95, 0.60) with γ = 1.0 and 1.5. We compute 4500 orbits in each model for time periods of 10 5 T D . We find that a large fraction of the orbits in each model are stochastic by means of their nonzero Liapunov exponents. The stochastic orbits in each model can sustain regular shapes for ∼10 3 T D or longer, which suggests that they diffuse slowly through their allowed phase-space. With the exception of the oblate triaxial models with y = 1.0, our attempts to construct self-consistent solutions employing only the regular orbits fail for the remaining three models. However, the self-consistent solutions are found to exist for all models when the stochastic and regular orbits are treated in the same way because the mixing-time, ∼10 4 T D , is shorter than the integration time, 10 5 T D . Moreover, the fully-mixed solutions can also be constructed for all models when the stochastic orbits are fully mixed at 15 lowest energy shells. Thus, we conclude that the self-consistent solutions exist for our selected prolate and oblate triaxial models withy = 1.0 and 1.5.

Self-similar dynamics of a magnetized polytropic gas

In broad astrophysical contexts of large-scale gravitational collapses and outflows and as a basis for various further astrophysical applications, we formulate and investigate a theoretical problem of self-similar magnetohydrodynamics (MHD) for a non-rotating polytropic gas of quasi-spherical symmetry permeated by a completely random magnetic field. Within this framework, we derive two coupled nonlinear MHD ordinary differential equations (ODEs), examine properties of the magnetosonic critical curve, obtain various asymptotic and global semi-complete similarity MHD solutions, and qualify the applicability of our results. Unique to a magnetized gas cloud, a novel asymptotic MHD solution for a collapsing core is established. Physically, the similarity MHD inflow towards the central dense core proceeds in characteristic manners before the gas material eventually encounters a strong radiating MHD shock upon impact onto the central compact object. Sufficiently far away from the central core region enshrouded by such an MHD shock, we derive regular asymptotic behaviours. We study asymptotic solution behaviours in the vicinity of the magnetosonic critical curve and determine smooth MHD eigensolutions across this curve. Numerically, we construct global semi-complete similarity MHD solutions that cross the magnetosonic critical curve zero, one, and two times. For comparison, counterpart solutions in the case of an isothermal unmagnetized and magnetized gas flows are demonstrated in the present MHD framework at nearly isothermal and weakly magnetized conditions. For a polytropic index γ=1.25 or a strong magnetic field, different solution behaviours emerge. With a strong magnetic field, there exist semi-complete similarity solutions crossing the magnetosonic critical curve only once, and the MHD counterpart of expansion-wave collapse solution disappears. Also in the polytropic case of γ=1.25, we no longer observe the trend in the speed-density phase diagram of finding infinitely many matches to establish global MHD solutions that cross the magnetosonic critical curve twice.

Spatiotemporal evolution of vortex dust structures in a track plasma

Results are presented from experimental studies of the behavior of dust grains in a track plasma produced by an accelerated proton beam. Dynamic dust structures in such a plasma are obtained for the first time, and their spatiotemporal evolution is thoroughly investigated. The structures develop from a dust spiral, which abruptly transforms with increasing dust density into a differentially rotating dust cloud across which dust-sound waves (including spiral waves generated by the dense central core) propagate. As time elapses, the dust cloud loses its fragments and gradually vanishes. At constant experimental conditions, the lifetime of the structures attains a few minutes.

An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MOND

We investigate the in-spiralling time-scales of globular clusters (GCs) in dwarf spheroidal (dSph) and dwarf elliptical (dE) galaxies, due to dynamical friction (DF). We address the problem of these time-scales having been variously estimated in the literature as much shorter than a Hubble time. Using self-consistent two-component (dark matter and stars) models, we explore mechanisms which may yield extended DF time-scales in such systems in order to explain why dwarf galaxies often show GC systems. As a general rule, dark matter and stars both give a comparable contribution to the dynamical drag. By exploring various possibilities for their gravitational make-up, it is shown that these studies help to constrain the parameters of the dark matter haloes in these galaxies, as well as to test alternatives to dark matter. Under the assumption of a dark halo having a central density core with a typical King core radius somewhat larger than the observed stellar core radius, DF time-scales are naturally extended upwards of a Hubble time. Cuspy dark haloes yield time-scales ≲4.5 Gyr, for any dark halo parameters in accordance with observations of stellar line-of-sight velocity dispersion in dSph galaxies. We confirm, after a detailed formulation of the DF problem under the alternative hypothesis of modified Newtonian dynamics (MOND) and in the lack of any dark matter, that due to the enhanced dynamical drag of the stars, the DF time-scales in MOND would be extremely short. Taking the well-measured structural parameters of the Fornax dSph and its GC system as a case study, we conclude that requiring DF time-scales comparable to the Hubble time strongly favours dark haloes with a central core.