We use smoothed particle hydrodynamic simulations of cold, uniform density, self-gravitating filaments, to investigate their longitudinal collapse time-scales; these time-scales are important because ...they determine the time available for a filament to fragment into cores. A filament is initially characterized by its line-mass, μO, its radius, R
O (or equivalently its density
$\rho _{{\rm O}}= \mu _{{\rm O}}/\pi R_{{\rm O}}^2$
), and its aspect ratio, A
O (≡Z
O/R
O, where Z
O is its half-length). The gas is only allowed to contract longitudinally, i.e. parallel to the symmetry axis of the filament (the z-axis). Pon et al. (2012) have considered the global dynamics of such filaments analytically. They conclude that short filaments (A
O ≲ 5) collapse along the z-axis more-or-less homologously, on a time-scale t
HOM ∼ 0.44 A
O (GρO)−1/2; in contrast, longer filaments (A
O ≳ 5) undergo end-dominated collapse, i.e. two dense clumps form at the ends of the filament and converge on the centre sweeping up mass as they go, on a time-scale
$t_{{\rm END}} \sim 0.98\,A_{{\rm O}}^{1/2}\,(G\rho _{{\rm O}})^{-1/2}$
. Our simulations do not corroborate these predictions. First, for all A
O ≳ 2, the collapse time satisfies a single equation
\begin{equation*}
t_{{\rm COL}}\sim (0.49+0.26A_{{\rm O}})(G\rho _{{\rm O}})^{-1/2}\,,
\end{equation*}
which for large A
O is much longer than the Pon et al. prediction. Secondly, for all A
O ≳ 2, the collapse is end-dominated. Thirdly, before being swept up, the gas immediately ahead of an end-clump is actually accelerated outwards by the gravitational attraction of the approaching clump, resulting in a significant ram pressure. For high aspect ratio filaments, the end-clumps approach an asymptotic inward speed, due to the fact that they are doing work both accelerating and compressing the gas they sweep up. Pon et al. appear to have neglected the outward acceleration and its consequences.
Perturbation growth in accreting filaments Clarke, S. D; Whitworth, A. P; Hubber, D. A
Monthly notices of the Royal Astronomical Society,
05/2016, Letnik:
458, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads ...to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.
The neutrophil lymphocyte ratio (NLR) has prognostic value in patients with a variety of cancers. Many chemotherapeutic trial databases hold information on white cell and neutrophil counts only. The ...aim of the present study was to compare the prognostic value of the NLR with a derived score (dNLR), composed of white cell and neutrophil counts.
Patients (n=27,031) who were sampled incidentally between 2000 and 2007 for neutrophil, lymphocyte and white cell counts, and also had a diagnosis of cancer (Scottish Cancer Registry), were identified. Of this group, 12,118 patients who had been sampled within 2 years of their cancer diagnosis were studied.
On follow-up, there were 7366 deaths, of which 6198 (84%) were cancer deaths. The median time from blood sampling to diagnosis was 2.1 months. The area under the receiver-operating characteristic (ROC) curve for cancer-specific survival was 0.650 for the NLR and 0.640 for the dNLR. The NLR and dNLR were independently associated with survival in all cancers studied (all P<0.001). The optimal thresholds, on the basis of hazard ratios and area under the curve, were 4 : 1 for the NLR and 2 : 1 for the dNLR.
The results of the present study show that the dNLR has similar prognostic value to the NLR. Therefore, the universally available dNLR is to be commended for use in the risk stratification of patients undergoing chemotherapy.
Rapid, accurate assessment of the yield of a large-scale urban explosion will assist in implementing emergency response plans, will facilitate better estimates of areas at risk of high damage and ...casualties, and will provide policy makers and the public with more accurate information about the event. On 4 August 2020, an explosion occurred in the Port of Beirut, Lebanon. Shortly afterwards, a number of videos were posted to social media showing the moment of detonation and propagation of the resulting blast wave. In this article, we present a method to rapidly calculate explosive yield based on analysis of 16 videos with a clear line-of-sight to the explosion. The time of arrival of the blast is estimated at 38 distinct positions, and the results are correlated with well-known empirical laws in order to estimate explosive yield. The best estimate and reasonable upper limit of the 2020 Beirut explosion determined from this method are 0.50 kt TNT and 1.12 kt TNT, respectively.
ABSTRACT
Recent observations have revealed the presence of small fibres or sub-filaments within larger filaments. We present a numerical fragmentation study of fibrous filaments investigating the ...link between cores and sub-filaments using hydrodynamical simulations performed with the moving-mesh code arepo. Our study suggests that cores form in two environments: (i) as isolated cores, or small chains of cores, on a single sub-filament, or (ii) as an ensemble of cores located at the junction of sub-filaments. We term these isolated and hub cores, respectively. We show that these core populations are statistically different from each other. Hub cores have a greater mean mass than isolated cores, and the mass distribution of hub cores is significantly wider than isolated cores. This fragmentation is reminiscent of parsec-scale hub-filament systems, showing that the combination of turbulence and gravity leads to similar fragmentation signatures on multiple scales, even within filaments. Moreover, the fact that fragmentation proceeds through sub-filaments suggests that there exists no characteristic fragmentation length-scale between cores. This is in opposition to earlier theoretical works studying fibre-less filaments which suggest a strong tendency towards the formation of quasi-periodically spaced cores, but in better agreement with observations. We also show tentative signs that global collapse of filaments preferentially form cores at both filament ends, which are more massive and dense than other cores.
Context.
Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ...ambient cloud during their evolution remain debated.
Aims.
We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation.
Methods.
We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2
12
CO(1–0) map of the full Musca cloud, H
I
emission of the Chamaeleon-Musca complex, a
Planck
polarisation map, line radiative transfer models,
Gaia
data, and synthetic observations from filament formation simulations.
Results.
The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (
n
H
2
∼ 10
4
cm
−3
) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at
T
~ 15 K and
n
H
2
∼ 10
3
cm
−3
is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived from
Planck
, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H
I
cloud down to the Musca filament. We also report a strong C
18
O/
13
CO abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2 pc in a weak ambient far-ultraviolet (FUV) field.
Conclusions.
The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H
I
cloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.
Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has ...developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests.
We find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes.
The extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera's invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
How molecular clouds fragment into dense structures that eventually form stars is an open question. We investigate the relative importance of gravity (both self-gravity and tidal forces) and ...the volume and surface terms of kinetic, thermal, and magnetic energy for the formation and evolution of molecular clouds and their substructures based on the SILCC-Zoom simulations. These simulations follow the self-consistent formation of cold molecular clouds down to scales of 0.1 pc from the diffuse supernova-driven interstellar medium in a stratified galactic disc. We study the time evolution of seven molecular clouds (of which five are magnetized) over ∼2 Myr. Using a dendrogram, we identify hierarchical three-dimensional substructures inside the clouds with the aim of understanding their dynamics. The virial analysis shows that the dense gas is indeed dominated by the interplay of gravity and turbulence, while magnetic fields and thermal pressure are mostly important for fluffy, atomic structures. However, not all bound structures are gravitationally bound; some are held together by ram pressure aided by other surface terms. Overall, ∼36 per cent of the clouds have >50 per cent of their mass in ‘potentially gravity bound’ structures. A subset of them (70 per cent) is ‘potentially bound’ by gravity on scales >15 pc. A detailed tidal analysis shows that the tidal tensor is highly anisotropic. Yet the tidal forces are generally not strong enough to disrupt either large-scale or dense substructures but cause their deformation. When comparing the tidal and crossing time-scales, we find that tidal forces do not appear to be the main driver of turbulence within the molecular clouds.
To review and synthesise prognostic indices that predict subsequent risk, prescriptive indices that moderate treatment response, and mechanisms that underlie each with respect to relapse and ...recurrence of depression in adults.
Childhood maltreatment, post-treatment residual symptoms, and a history of recurrence emerged as strong prognostic indicators of risk and each could be used prescriptively to indicate who benefits most from continued or prophylactic treatment. Targeting prognostic indices or their “down-stream” consequences will be particularly beneficial because each is either a cause or a consequence of the causal mechanisms underlying risk of recurrence. The cognitive and neural mechanisms that underlie the prognostic indices are likely addressed by the effects of treatments that are moderated by the prescriptive factors. For example, psychosocial interventions that target the consequences of childhood maltreatment, extending pharmacotherapy or adapting psychological therapies to deal with residual symptoms, or using cognitive or mindfulness-based therapies for those with prior histories of recurrence. Future research that focuses on understanding causal pathways that link childhood maltreatment, or cognitive diatheses, to dysfunction in the neocortical and limbic pathways that process affective information and facilitate cognitive control, might result in more enduring effects of treatments for depression.
•Prognostic risk factors for recurrence were in order of strength of evidence:•1st: childhood maltreatment, residual symptoms and history of prior episodes•2nd: comorbid anxiety, rumination, neuroticism and age of onset•Some also may be prescriptive but evidence for such effects was limited•Neurocognitive and neuroendocrine factors were identified as potential risk factors•A conceptual framework considering the risk factors and mechanisms was developed.
ABSTRACT
We have analysed the Herschel and SCUBA-2 dust continuum observations of the main filament in the Taurus L1495 star-forming region, using the Bayesian fitting procedure ppmap. (i) If we ...construct an average profile along the whole length of the filament, it has FWHM $\simeq 0.087\pm 0.003\, {\rm pc};\,\,$ but the closeness to previous estimates is coincidental. (ii) If we analyse small local sections of the filament, the column-density profile approximates well to the form predicted for hydrostatic equilibrium of an isothermal cylinder. (iii) The ability of ppmap to distinguish dust emitting at different temperatures, and thereby to discriminate between the warm outer layers of the filament and the cold inner layers near the spine, leads to a significant reduction in the surface-density, $\varSigma$, and hence in the line-density, μ. If we adopt the canonical value for the critical line-density at a gas-kinetic temperature of $10\, {\rm K}$, $\mu _{{\rm CRIT}}\simeq 16\, {\rm M_{\odot }\, pc^{-1}}$, the filament is on average trans-critical, with ${\bar{\mu }}\sim \mu _{{\rm CRIT}};\,\,$ local sections where μ > μCRIT tend to lie close to prestellar cores. (iv) The ability of ppmap to distinguish different types of dust, i.e. dust characterized by different values of the emissivity index, β, reveals that the dust in the filament has a lower emissivity index, β ≲ 1.5, than the dust outside the filament, β ≳ 1.7, implying that the physical conditions in the filament have effected a change in the properties of the dust.
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