8 research outputs found
An Initial Mass Function Study of the Dwarf Starburst Galaxy NGC 4214
The production rate of ionizing photons in young (≤8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass to investigate the upper end of the stellar initial mass function (IMF). We have found that within the uncertainties the upper end of the stellar IMF appears to be universal in this galaxy, and that deviations from a universal IMF can be attributed to stochastic sampling of stars in clusters with masses ≾ 10^3 M_☉. Furthermore, we have found that there does not seem to be a dependence of the maximum stellar mass on the cluster mass. We have also found that for massive clusters, feedback may cause an underrepresentation in Hα luminosities, which needs to be taken into account when conducting this type of analysis
Crack-Like Processes Governing the Onset of Frictional Slip
We perform real-time measurements of the net contact area between two blocks
of like material at the onset of frictional slip. We show that the process of
interface detachment, which immediately precedes the inception of frictional
sliding, is governed by three different types of detachment fronts. These
crack-like detachment fronts differ by both their propagation velocities and by
the amount of net contact surface reduction caused by their passage. The most
rapid fronts propagate at intersonic velocities but generate a negligible
reduction in contact area across the interface. Sub-Rayleigh fronts are
crack-like modes which propagate at velocities up to the Rayleigh wave speed,
VR, and give rise to an approximate 10% reduction in net contact area. The most
efficient contact area reduction (~20%) is precipitated by the passage of slow
detachment fronts. These fronts propagate at anomalously slow velocities, which
are over an order of magnitude lower than VR yet orders of magnitude higher
than other characteristic velocity scales such as either slip or loading
velocities. Slow fronts are generated, in conjunction with intersonic fronts,
by the sudden arrest of sub-Rayleigh fronts. No overall sliding of the
interface occurs until either of the slower two fronts traverses the entire
interface, and motion at the leading edge of the interface is initiated. Slip
at the trailing edge of the interface accompanies the motion of both the slow
and sub-Rayleigh fronts. We might expect these modes to be important in both
fault nucleation and earthquake dynamics.Comment: 19 page, 5 figures, to appear in International Journal of Fractur
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Surgical Approaches to Thalamic Gliomas: A Systematic Review
Adult thalamic gliomas (ATG) present a surgical challenge given their depth and proximity to eloquent brain regions. Choosing a surgical approach relies on different clinical variables such as anatomical location, and size of the tumor. However, conclusive data regarding how these variables influence the balance between extent of resection and complications is lacking. We aim to systematically review the literature to describe the current surgical outcomes of ATG and to provide tools that may improve the decision-making process.
Literature regarding the surgical management of ATG patients was reviewed according to the PRISMA guidelines. Four databases were queried and a description of clinical characteristics and survival analysis was performed. An individual patient data (IPD) analysis was conducted when feasible.
A total of 462 patients were included from 13 studies. The mean age was 39.8 years with a median preoperative KPS of 70. The lateral approaches were most frequently used (74.9%), followed by the interhemispheric (24.2%). Gross total and subtotal/partial resections were achieved in 81%, and 19% of all cases, respectively. New permanent neurological deficits were observed in 51/433 patients (11.8%). IPD was pooled from five studies (n = 71). In the multivariate analysis, tumors located within the posterior thalamus had worse median overall survival compared to anterior gliomas (14.5 vs. 27 months, p=0.003).
Surgical resection of adult thalamic gliomas can increase survival but at the risk of operative morbidity. Knowing which factors impact survival may allow neurosurgeons to propose a more evidence-based treatment to their patients
An initial mass function study of the dwarf starburst galaxy NGC 4214
The production rate of ionizing photons in young (≤8 Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass
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