Mode identification in rapidly rotating stars

Context: Recent calculations of pulsation modes in rapidly rotating polytropic models and models based on the Self-Consistent Field method have shown that the frequency spectrum of low degree pulsation modes can be described by an empirical formula similar to Tassoul's asymptotic formula, provided that the underlying rotation profile is not too differential. Aims: Given the simplicity of this asymptotic formula, we investigate whether it can provide a means by which to identify pulsation modes in rapidly rotating stars. Methods: We develop a new mode identification scheme which consists in scanning a multidimensional parameter space for the formula coefficients which yield the best-fitting asymptotic spectra. This mode identification scheme is then tested on artificial spectra based on the asymptotic formula, on random frequencies and on spectra based on full numerical eigenmode calculations for which the mode identification is known beforehand. We also investigate the effects of adding random frequencies to mimic the effects of chaotic modes which are also expected to show up in such stars. Results: In the absence of chaotic modes, it is possible to accurately find a correct mode identification for most of the observed frequencies provided these frequencies are sufficiently close to their asymptotic values. The addition of random frequencies can very quickly become problematic and hinder correct mode identification. Modifying the mode identification scheme to reject the worst fitting modes can bring some improvement but the results still remain poorer than in the case without chaotic modes

Words are Malleable: Computing Semantic Shifts in Political and Media Discourse

Recently, researchers started to pay attention to the detection of temporal shifts in the meaning of words. However, most (if not all) of these approaches restricted their efforts to uncovering change over time, thus neglecting other valuable dimensions such as social or political variability. We propose an approach for detecting semantic shifts between different viewpoints--broadly defined as a set of texts that share a specific metadata feature, which can be a time-period, but also a social entity such as a political party. For each viewpoint, we learn a semantic space in which each word is represented as a low dimensional neural embedded vector. The challenge is to compare the meaning of a word in one space to its meaning in another space and measure the size of the semantic shifts. We compare the effectiveness of a measure based on optimal transformations between the two spaces with a measure based on the similarity of the neighbors of the word in the respective spaces. Our experiments demonstrate that the combination of these two performs best. We show that the semantic shifts not only occur over time, but also along different viewpoints in a short period of time. For evaluation, we demonstrate how this approach captures meaningful semantic shifts and can help improve other tasks such as the contrastive viewpoint summarization and ideology detection (measured as classification accuracy) in political texts. We also show that the two laws of semantic change which were empirically shown to hold for temporal shifts also hold for shifts across viewpoints. These laws state that frequent words are less likely to shift meaning while words with many senses are more likely to do so.Comment: In Proceedings of the 26th ACM International on Conference on Information and Knowledge Management (CIKM2017

On the Space Time of a Galaxy

We present an exact solution of the averaged Einstein's field equations in the presence of two real scalar fields and a component of dust with spherical symmetry. We suggest that the space-time found provides the characteristics required by a galactic model that could explain the supermassive central object and the dark matter halo at once, since one of the fields constitutes a central oscillaton surrounded by the dust and the other scalar field distributes far from the coordinate center and can be interpreted as a halo. We show the behavior of the rotation curves all along the background. Thus, the solution could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure

Substructure and halo density profiles in a Warm Dark Matter Cosmology

We performed a series of high-resolution simulations designed to study the substructure of Milky Way-size galactic halos (host halos) and the density profiles of halos in a warm dark matter (WDM) scenario with a non-vanishing cosmological constant. The virial masses of the host halos range from 3.5 x 10^12 to 1.7 x 10^12 solar masses and they have more than 10^5 particles each. A key feature of the WDM power spectrum is the free-streaming length R_f which fixes an additional parameter for the model of structure formation. We analyze the substructure of host halos using three R_f values: 0.2, 0.1, and 0.05 Mpc and compare results to the predictions of the cold dark matter (CDM) model. We find that guest halos (satellites) do form in the WDM scenario but are more easily destroyed by dynamical friction and tidal disruption than their counterparts in a CDM model. The small number of guest halos that we find within the virial radii of host halos at z = 0 in the WDM models is the result of a less efficient halo accretion and a higher satellite destruction rate. Under the assumption that each guest halo hosts a luminous galaxy, we find that the observed circular velocity function of satellites around the Milky Way and Andromeda is well described by the R_f = 0.1 Mpc WDM model. In the R_f = 0.1-0.2 Mpc models, the surviving subhalos at z=0 have an average concentration parameter c_1/5 which is approximately twice smaller than that of the corresponding CDM subhalos. This difference, very likely, produces the higher satellite destruction rate found in the WDM models. The density profile of host halos is well described by the NFW fit whereas guest halos show a wide variety of density profiles (abridged).Comment: Uses emulateapj.sty: 10 pages, 4 figures, ApJ accepted. Some changes have been introduced as suggested by the referee: (1) the description of the numerical simulations was sligthly modified to make it clearer, (2) the ellipticities of the host halos are now measured, and (3) the discussion section was divided in two subsections and enlarge

Application of iChip to Grow “Uncultivable” Microorganisms and its Impact on Antibiotic Discovery

Purpose. Antibiotics have revolutionized modern medicine, allowing significant progress in healthcare and improvement in life expectancy. Development of antibiotic resistance by pathogenic bacteria is a natural phenomenon; however, the rate of antibiotic resistance emergence is increasing at an alarming rate, due to indiscriminate use of antibiotics in healthcare, agriculture and even everyday products. Traditionally, antibiotic discovery has been conducted by screening extracts of microorganisms for antimicrobial activity. However, this conventional source has been over-used to such an extent that it poses the risk of “running out” of new antibiotics. Aiming to increase access to a greater diversity of microorganisms, a new cultivation method with an in situ approach called iChip has been designed. The iChip has already isolated many novel organisms, as well as Teixobactin, a novel antibiotic with significant potency against Gram-positive bacteria

Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution

We discuss the dissipation of turbulent kinetic energy Ek in the global ISM by means of 2-D, MHD, non-isothermal simulations in the presence of model radiative heating and cooling. We argue that dissipation in 2D is representative of that in three dimensions as long as it is dominated by shocks rather than by a turbulent cascade. Energy is injected at a few isolated sites in space, over relatively small scales, and over short time periods. This leads to the coexistence of forced and decaying regimes in the same flow. We find that the ISM-like flow dissipates its turbulent energy rapidly. In simulations with forcing, the input parameters are the radius l_f of the forcing region, the total kinetic energy e_k each source deposits into the flow, and the rate of formation of those regions, sfr_OB. The global dissipation time t_d depends mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >= 1.5x10^7 yr. The global dissipation time is consistently smaller than the crossing time of the largest energy-containing scales. In decaying simulations, Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If applicable to the vertical direction, our results support models of galaxy evolution in which stellar energy injection provides significant support for the gas disk thickness, but not models of galaxy formation in which this energy injection is supposed to reheat an intra-halo medium at distances of up to 10-20 times the optical galaxy size, as the dissipation occurs on distances comparable to the disk height.Comment: 23 pages, including figures. To appear in ApJ. Abstract abridge

Using hand proportions to test taxonomic boundaries within the \u3ci\u3eTupaia glis\u3c/i\u3e species complex (Scandentia, Tupaiidae)

Treeshrews (order Scandentia) comprise 2 families of squirrel-sized terrestrial, arboreal, and scansorial mammals distributed throughout much of tropical South and Southeast Asia. The last comprehensive taxonomic revision of treeshrews was published in 1913, and a well-supported phylogeny clarifying relationships among all currently recognized extant species within the order has only recently been published. Within the family Tupaiidae, 2 widely distributed species, the northern treeshrew, Tupaia belangeri (Wagner, 1841), and the common treeshrew, T. glis (Diard, 1820), represent a particularly vexing taxonomic complex. These 2 species are currently distinguished primarily based on their respective distributions north and south of the Isthmus of Kra on the Malay Peninsula and on their different mammae counts. This problematic species complex includes 54 published synonyms, many of which represent putative island endemics. The widespread T. glis and T. belangeri collectively comprise a monophyletic assemblage representing the sister lineage to a clade composed of the golden-bellied treeshrew, T. chrysogaster Miller, 1903 (Mentawai Islands), and the long-footed treeshrew, T. longipes (Thomas, 1893) (Borneo). As part of a morphological investigation of the T. glis–T. belangeri complex, we studied the proportions of hand bones, which have previously been shown to be useful in discriminating species of soricids (true shrews). We measured 38 variables from digital X-ray images of 148 museum study skins representing several subspecies of T. glis, T. belangeri, T. chrysogaster, and T. longipes and analyzed these data using principal components and cluster analyses. Manus proportions among these 4 species readily distinguish them, particularly in the cases of T. chrysogaster and T. longipes. We then tested the distinctiveness of several of the populations comprising T. glis and T. longipes. T. longipes longipes and T. l. salatana Lyon, 1913, are distinguishable from each other, and populations of T. ‘‘glis’’ from Bangka Island and Sumatra are distinct from those on the Malay Peninsula, supporting the recognition of T. salatana, T. discolor Lyon, 1906, and T. ferruginea Raffles, 1821 as distinct species in Indonesia. These relatively small, potentially vulnerable treeshrew populations occur in the Sundaland biodiversity hotspot and will require additional study to determine their appropriate conservation status

Using hand proportions to test taxonomic boundaries within the \u3ci\u3eTupaia glis\u3c/i\u3e species complex (Scandentia, Tupaiidae)

Treeshrews (order Scandentia) comprise 2 families of squirrel-sized terrestrial, arboreal, and scansorial mammals distributed throughout much of tropical South and Southeast Asia. The last comprehensive taxonomic revision of treeshrews was published in 1913, and a well-supported phylogeny clarifying relationships among all currently recognized extant species within the order has only recently been published. Within the family Tupaiidae, 2 widely distributed species, the northern treeshrew, Tupaia belangeri (Wagner, 1841), and the common treeshrew, T. glis (Diard, 1820), represent a particularly vexing taxonomic complex. These 2 species are currently distinguished primarily based on their respective distributions north and south of the Isthmus of Kra on the Malay Peninsula and on their different mammae counts. This problematic species complex includes 54 published synonyms, many of which represent putative island endemics. The widespread T. glis and T. belangeri collectively comprise a monophyletic assemblage representing the sister lineage to a clade composed of the golden-bellied treeshrew, T. chrysogaster Miller, 1903 (Mentawai Islands), and the long-footed treeshrew, T. longipes (Thomas, 1893) (Borneo). As part of a morphological investigation of the T. glis–T. belangeri complex, we studied the proportions of hand bones, which have previously been shown to be useful in discriminating species of soricids (true shrews). We measured 38 variables from digital X-ray images of 148 museum study skins representing several subspecies of T. glis, T. belangeri, T. chrysogaster, and T. longipes and analyzed these data using principal components and cluster analyses. Manus proportions among these 4 species readily distinguish them, particularly in the cases of T. chrysogaster and T. longipes. We then tested the distinctiveness of several of the populations comprising T. glis and T. longipes. T. longipes longipes and T. l. salatana Lyon, 1913, are distinguishable from each other, and populations of T. ‘‘glis’’ from Bangka Island and Sumatra are distinct from those on the Malay Peninsula, supporting the recognition of T. salatana, T. discolor Lyon, 1906, and T. ferruginea Raffles, 1821 as distinct species in Indonesia. These relatively small, potentially vulnerable treeshrew populations occur in the Sundaland biodiversity hotspot and will require additional study to determine their appropriate conservation status