Star Formation in Transient Molecular Clouds

We present the results of a numerical simulation in which star formation proceeds from an initially unbound molecular cloud core. The turbulent motions, which dominate the dynamics, dissipate in shocks leaving a quiescent region which becomes gravitationally bound and collapses to form a small multiple system. Meanwhile, the bulk of the cloud escapes due to its initial supersonic velocities. In this simulation, the process naturally results in a star formation efficiency of 50%. The mass involved in star formation depends on the gas fraction that dissipates sufficient kinetic energy in shocks. Thus, clouds with larger turbulent motions will result in lower star formation efficiencies. This implies that globally unbound, and therefore transient giant molecular clouds (GMCs), can account for the low efficiency of star formation observed in our Galaxy without recourse to magnetic fields or feedback processes. Observations of the dynamic stability in molecular regions suggest that GMCs may not be self-gravitating, supporting the ideas presented in this letter.Comment: 5 pages, 3 figures, accepted for MNRAS as a lette

The star formation efficiency and its relation to variations in the initial mass function

We investigate how the dynamical state of a turbulently supported, 1000 solar mass, molecular cloud affects the properties of the cluster it forms, focusing our discussion on the star formation efficiency (SFE) and the initial mass function (IMF). A variety of initial energy states are examined in this paper, ranging from clouds with PE = 0.1 KE to clouds with PE = 10 KE, and for both isothermal and piece-wise polytropic equations of state (similar to that suggested by Larson). It is found that arbitrary star formation efficiencies are possible, with strongly unbound clouds yielding very low star formation efficiencies. We suggest that the low star formation efficiency in the Maddelena cloud may be a consequence of the relatively unbound state of its internal structure. It is also found that competitive accretion results in the observed IMF when the clouds have initial energy states of PE >= KE. We show that under such conditions the shape of the IMF is independent of time in the calculations. This demonstrates that the global accretion process can be terminated at any stage in the cluster's evolution, while still yielding a distribution of stellar masses that is consistent with the observed IMF. As the clouds become progressively more unbound, competitive accretion is less important and the protostellar mass function flattens. These results predict that molecular clouds should be permeated with a distributed population of stars that follow a flatter than Salpeter IMF.Comment: 8 pages, 6 figures, accepted by MNRAS for publictaion. Now available through the 'Online Early' schem

Clump Lifetimes and the Initial Mass Function

Recent studies of dense clumps/cores in a number of regions of low-mass star formation have shown that the mass distribution of these clumps closely resembles the initial mass function (IMF) of field stars. One possible interpretation of these observations is that we are witnessing the fragmentation of the clouds into the IMF, and the observed clumps are bound pre-stellar cores. In this paper, we highlight a potential difficulty in this interpretation, namely that clumps of varying mass are likely to have systematically varying lifetimes. This timescale problem can effectively destroy the similarity bewteen the clump and stellar mass functions, such that a stellar-like clump mass function (CMF) results in a much steeper stellar IMF. We also discuss some ways in which this problem may be avoided.Comment: 7 pages, 3 figures, accepted to MNRA

Far Term Noise Reduction Roadmap for the NASA D8 and Single-Aisle Tube-And-Wing Aircraft Concepts

A portfolio of noise reduction technologies is applied to two advanced single-aisle class vehicle concepts in order to evaluate the prospects for these aircraft to meet the NASA Far Term noise goals, beyond 2035. TheNASAD8 (ND8) aircraft is an unconventional configuration with boundary-layer ingesting engines mounted in the aft dorsal location. The 160-passenger tube-and-wing (TW160) aircraft is a conventional configuration with podded engines located under the wing, which represents an incremental evolution of current design philosophies. The noise reduction technologies were chosen to be compatible with each aircrafts specific configuration requirements. The acoustic effects were predicted based on experimental and numerical studies, andwere incorporated into the prediction of total system noise usingNASAs research-level Aircraft NOise Prediction Program (ANOPP-Research). Results suggest that the unfavorable Propulsion Airframe Aeroacoustic (PAA) effects of the two aircraft considered here significantly limit their prospects of meeting NASAs Far Term noise goal, and that further development of the technology portfolio is key to ensuring future success in addressing the noise challenges for single-aisle class vehicles

Release of cognitive and multimodal MRI data including real-world tasks and hippocampal subfield segmentations

We share data from N = 217 healthy adults (mean age 29 years, range 20-41; 109 females, 108 males) who underwent extensive cognitive assessment and neuroimaging to examine the neural basis of individual differences, with a particular focus on a brain structure called the hippocampus. Cognitive data were collected using a wide array of questionnaires, naturalistic tests that examined imagination, autobiographical memory recall and spatial navigation, traditional laboratory-based tests such as recalling word pairs, and comprehensive characterisation of the strategies used to perform the cognitive tests. 3 Tesla MRI data were also acquired and include multi-parameter mapping to examine tissue microstructure, diffusion-weighted MRI, T2-weighted high-resolution partial volume structural MRI scans (with the masks of hippocampal subfields manually segmented from these scans), whole brain resting state functional MRI scans and partial volume high resolution resting state functional MRI scans. This rich dataset will be of value to cognitive and clinical neuroscientists researching individual differences, real-world cognition, brain-behaviour associations, hippocampal subfields and more. All data are freely available on Dryad

Far Term Noise Reduction Technology Roadmap for a Large Twin-Aisle Tube-And-Wing Subsonic Transport

Interest in unconventional aircraft architectures has steadily increased over the past several decades. However, each of these concepts has several technical challenges to overcome before maturing to the point of commercial acceptance. In the interim, it is important to identify any technologies that will enhance the noise reduction of conventional tube-and-wing aircraft. A technology roadmap with an assumed acoustic technology level of a 2035 entry into service is established for a large twin-aisle, tube-and-wing architecture to identify which technologies provide the most noise reduction. The noise reduction potential of the architecture relative to NASA noise goals is also assessed. The current roadmap estimates only a 30 EPNdB cumulative margin to Stage 4 for this configuration of a tube-and-wing aircraft with engines under the wing. This falls short of reaching even the 2025 Mid Term NASA goal (32 EPNdB) in the Far Term time frame. Specifically, the lack of additional technologies to reduce the aft fan noise and the corresponding installation effects is the key limitation of the noise reduction potential of the aircraft. Under the same acoustic technology assumptions, unconventional architectures are shown to offer an 810 EPNdB benefit from favorable relative placement of the engine when integrated to the airframe

Diplomski studiji javne uprave i javnih politika: analiza sveučilišnih programa i stručnih kompetencija u Kanadi

We review Canadian Master’s of Public Administration and Master’s of Public Policy (MPA/MPP) academic programs by examining both general curricula but also – using a new web tool called the Public Policy and Governance (PPG) Portal – the detailed content (concepts) taught in those courses and their match with »competencies« as defined by several international public administration standards setting organizations. In total, we examined 22 academic units across the country, which in total offered 33 distinct programs (some units offered more than one program). We also provide data on certificate and diploma programs and their various concentrations. Despite the variety in programming (jurisdiction over education in Canada is at the sub-national or provincial level, with a relatively high degree of autonomy for individual universities, unlike the more national-state dominated systems in the European tradition), we note several trends: most programs offer concentrations; a recent trend has been »hybrid« degrees (often combining administration or management with some aspect of international relations); a general reliance on internships; a set of core courses for most programs consisting of governance, macroeconomics, theory of public administration; research methods; public policy; quantitative methods. Using the PPG Portal, we were able to match detailed content of courses and curricula with the competencies template. We find that most Canadian programs fall short in offering (or requiring) courses in »policy analysis theory and techniques« and »implementation strategy and design«. We close with a call for better dialogue between academics and practitioners specifically in the Canadian case, but more generally, since MPA and MPP programs are professional degrees that prepare candidates for work in the public sector. The academic »supply« should at least be cognizant of the practitioner »demand«. We think that the PPG portal and the design and data-gathering that produced it provide a possible model for inquiries in other countries on the fit between academic programs and practical needs.Analiziraju se kanadski sveučilišni programi diplomskih studija javne uprave i diplomskih studija javnih politika pregledom općih programa studija, ali i korištenjem novog web alata nazvanog Portal za javne politike i upravu, koji detaljno analizira sadržaj (koncepte) koji se predaju na takvim studijima te ih automatski povezuje s kompetencijama koje se stječu. Njih je pak definiralo nekoliko međunarodnih organizacija koje se bave postavljanjem standarda na području javne uprave. Ukupno su pregledane 22 sveučilišne institucije iz cijele države, s ukupno 33 različita programa (neke institucije nude više programa). Daju se i podaci o potvrdama i diplomama o završenoj naobrazbi i različitim modulima koji postoje. Iako su programi raznoliki (obrazovanje u Kanadi spada u nadležnost federalnih jedinica – provincija, a sveučilišta imaju relativno visok stupanj autonomije, za razliku od europske tradicije u kojoj visokim školstvom dominiraju središnje vlasti), primjetno je nekoliko trendova: većina programa nudi module; najnoviji su trend »hibridne« diplome (u kojima se često kombiniraju uprava i menadžment s nekim vidom međunarodnih odnosa); opće oslanjanje na stažiranje u odgovarajućim institucijama; većina programa ima skup temeljnih predmeta koji se sastoji od upravljanja, makroekonomije, teorije javne uprave, metoda istraživanja, javnih politika te kvantitativnih metoda. Korištenjem Portala za javne politike uspjelo se usporediti detaljan sadržaj predmeta i programa s kompetencijama koje bi se trebale steći završetkom studija. Pronađeno je da je većina kanadskih programa podbacila u ponudi (ili traženju) predmeta vezanih za »teoriju i tehnike analize javnih politika« i »strategiju i oblikovanje provedbe«. Poziva se na bolju suradnju između akademske zajednice i praktičara, posebno u kanadskim prilikama, ali i općenito, budući da su diplomski studiji javne uprave i javnih politika profesionalni studiji koji pripremaju kandidate za zanimanje u javnom sektoru. Sveučilišna »ponuda« trebala bi biti barem minimalno uzeti u obzir »potražnju« prakse. Smatra se da Portal za javne politike i upravu, kao i oblikovanje i sakupljanje podataka koji su omogućili njegovo postojanje, mogu biti jedan od modela za istraživanja o istim temama i u drugim zemljama

Clumpy shocks and the clump mass function

In this paper, we examine whether clumpy, colliding, flows could be responsible for the clump mass functions that have been observed in several regions of embedded star formation, which have been shown to be described by a Salpeter type slope. The flows presented here, which comprise a population of initially identical clumps and the calculations are performed with and without the inclusion of self-gravity. When the shock region is at its densest, we find that the clump mass spectrum is always well modelled by a Salpeter type slope. This is true regardless of whether the self-gravity is included in the simulations or not. In the non-self-gravitating simulations, this slope is retained at lower Mach numbers (Mach 5 and 10) as the simulations progress past the densest phase. In the simulations which include self-gravity, we find that low Mach number runs yield a flatter mass function after the densest phase. This is simply a result of increased coagulation due to gravitational collapse of the flows. In the high Mach number runs (Mach 20) the Salpeter slope is always lost. The self gravitating calculations also show that the sub-group of gravitationally bound clumps in which star formation occurs, always contain the most massive clumps in the population. The mass function of these bound star forming clumps is not at all similar to the Salpeter type mass function observed for stars in the field. We conclude that the clump mass function may not only have nothing to do with gravity, but also nothing to do with the star formation process and the resulting mass distribution of stars. This raises doubt over the claims that the clump mass function is the origin of the stellar IMF, for regions such as rho Oph, Serpens and the Orion B cloud.Comment: Accepted for publication in MNRAS. 10 pages, 4 figures and 1 tabl

Posterior hippocampal CA2/3 volume is associated with autobiographical memory recall ability in lower performing individuals

People vary substantially in their capacity to recall past experiences, known as autobiographical memories. Here we investigated whether the volumes of specific hippocampal subfields were associated with autobiographical memory retrieval ability. We manually segmented the full length of the two hippocampi in 201 healthy young adults into DG/CA4, CA2/3, CA1, subiculum, pre/parasubiculum and uncus, in the largest such manually segmented subfield sample yet reported. Across the group we found no evidence for an association between any subfield volume and autobiographical memory recall ability. However, when participants were assigned to lower and higher performing groups based on their memory recall scores, we found that bilateral CA2/3 volume was significantly and positively associated with autobiographical memory recall performance specifically in the lower performing group. We further observed that this effect was attributable to posterior CA2/3. By contrast, semantic details from autobiographical memories, and performance on a range of laboratory-based memory tests, did not correlate with CA2/3 volume. Overall, our findings highlight that posterior CA2/3 may be particularly pertinent for autobiographical memory recall. They also reveal that there may not be direct one-to-one mapping of posterior CA2/3 volume with autobiographical memory ability, with size mattering perhaps only in those with poorer memory recall