1,725 research outputs found
Living in the Milky Way
It’s finally here. Today, June 20 at 6:34 p.m., is the the summer solstice, also known as the first day of summer and, confusingly enough, midsummer’s eve. From a scientific perspective, it marks the moment the sun reaches its northernmost point in our sky. As a result of that position, it’s the shortest night and longest day if you live north of the equator. [excerpt
Back Half of the Year
Here we are in the back half of 2016, and the days are getting shorter. We have, as of today, lost 18 minutes since the solstice on June 20, and the speed of that change is quickening. You may wonder why it is that we have our hottest weather after our longest day is behind us. The simple answer is that it takes time for land and water masses to warm up. That’s the reason that Sept. 21 is likely to be a lot warmer than March 21, even though they have the same amount of daylight. [excerpt
What Would Happen If You Ditched Your Textbook? Gettysburg Faculty Share Strategies
How much do your course materials really cost? Do your students obtain all the books you assign? How much does access to required readings affect student success? What would happen if you ditched your textbook?
If you’ve ever been tempted to toss your conventional reading list out the window and start over, this session is for you. Learn how colleagues are swapping out expensive course materials for more affordable options, including freely available materials, library-licensed items, and original creations. Our panelists are: Ian Clarke – Ian recently abandoned his $150 textbook for ENG 111 (Writing through Literature) and created an open reading list instead. Sharon Birch – In 2011, Sharon dropped the classic text for SOC 203 (Population) and replaced it with a variety of library-licensed and freely available materials. More recently she has begun developing her own open textbook for this course. Chuck Kann – Chuck has written several open educational resources and posted them in The Cupola. He uses them in CS 221 (Computer Organization and Assembly Language Programming); they have also been adopted by professors teaching at other institutions and have been downloaded around the world.
You’ll leave with a clear idea of how a range of simple to complex strategies could help make your course materials more affordable, too
The effect of a youth mental health service model on access to secondary mental healthcare for young people aged 14–25 years
Aims and method: The Norfolk Youth Service was created in 2012 in response to calls to redesign mental health services to better meet the needs of young people. The new service model transcends traditional boundaries by creating a single, ‘youth friendly’ service for young people aged 14–25 years. The aim of this study was to investigate the effect of the transition to this new model on patterns of referral, acceptance and service use. We analysed routinely collected data on young people aged 14–25 years referred for secondary mental healthcare in Norfolk before and after implementation of the youth mental health service. The number of referrals, their age and gender, proportion of referrals accepted and average number of service contacts per referral by age pre- and post-implementation were compared. Results: Referrals increased by 68% following implementation of the new service model, but the proportion of referrals accepted fell by 27 percentage points. Before implementation of the youth service, there was a clear discrepancy between the peak age of referral and the age of those seen by services. Following implementation, service contacts were more equitable across ages, with no marked discontinuity at age 18 years. Clinical implications: Our findings suggest that the transformation of services may have succeeded in reducing the ‘cliff edge’ in access to mental health services at the transition to adulthood. However, the sharp rise in referrals and reduction in the proportion of referrals accepted highlights the importance of considering possible unintended consequences of new service models. Declaration of interests: None
Gravitational fragmentation and the formation of brown dwarfs in stellar clusters
We investigate the formation of brown dwarfs and very low-mass stars through
the gravitational fragmentation of infalling gas into stellar clusters. The
gravitational potential of a forming stellar cluster provides the focus that
attracts gas from the surrounding molecular cloud. Structures present in the
gas grow, forming filaments flowing into the cluster centre. These filaments
attain high gas densities due to the combination of the cluster potential and
local self-gravity. The resultant Jeans masses are low, allowing the formation
of very low-mass fragments. The tidal shear and high velocity dispersion
present in the cluster preclude any subsequent accretion thus resulting in the
formation of brown dwarfs or very low-mass stars. Ejections are not required as
the brown dwarfs enter the cluster with high relative velocities, suggesting
that their disc and binary properties should be similar to that of low-mass
stars. This mechanism requires the presence of a strong gravitational potential
due to the stellar cluster implying that brown dwarf formation should be more
frequent in stellar clusters than in distributed populations of young stars.
Brown dwarfs formed in isolation would require another formation mechanism such
as due to turbulent fragmentation.Comment: 8 pages, 7 figures. MNRAS, in pres
Verifying Temporal Regular Properties of Abstractions of Term Rewriting Systems
The tree automaton completion is an algorithm used for proving safety
properties of systems that can be modeled by a term rewriting system. This
representation and verification technique works well for proving properties of
infinite systems like cryptographic protocols or more recently on Java Bytecode
programs. This algorithm computes a tree automaton which represents a (regular)
over approximation of the set of reachable terms by rewriting initial terms.
This approach is limited by the lack of information about rewriting relation
between terms. Actually, terms in relation by rewriting are in the same
equivalence class: there are recognized by the same state in the tree
automaton.
Our objective is to produce an automaton embedding an abstraction of the
rewriting relation sufficient to prove temporal properties of the term
rewriting system.
We propose to extend the algorithm to produce an automaton having more
equivalence classes to distinguish a term or a subterm from its successors
w.r.t. rewriting. While ground transitions are used to recognize equivalence
classes of terms, epsilon-transitions represent the rewriting relation between
terms. From the completed automaton, it is possible to automatically build a
Kripke structure abstracting the rewriting sequence. States of the Kripke
structure are states of the tree automaton and the transition relation is given
by the set of epsilon-transitions. States of the Kripke structure are labelled
by the set of terms recognized using ground transitions. On this Kripke
structure, we define the Regular Linear Temporal Logic (R-LTL) for expressing
properties. Such properties can then be checked using standard model checking
algorithms. The only difference between LTL and R-LTL is that predicates are
replaced by regular sets of acceptable terms
Massive star formation: Nurture, not nature
We investigate the physical processes which lead to the formation of massive
stars. Using a numerical simulation of the formation of a stellar cluster from
a turbulent molecular cloud, we evaluate the relevant contributions of
fragmentation and competitive accretion in determining the masses of the more
massive stars. We find no correlation between the final mass of a massive star,
and the mass of the clump from which it forms. Instead, we find that the bulk
of the mass of massive stars comes from subsequent competitive accretion in a
clustered environment. In fact, the majority of this mass infalls onto a
pre-existing stellar cluster. Furthermore, the mass of the most massive star in
a system increases as the system grows in numbers of stars and in total mass.
This arises as the infalling gas is accompanied by newly formed stars,
resulting in a larger cluster around a more massive star. High-mass stars gain
mass as they gain companions, implying a direct causal relationship between the
cluster formation process, and the formation of higher-mass stars therein.Comment: 8 pages, accepted for publication in MNRAS. Version including hi-res
colour postscript figure available at
http://star-www.st-and.ac.uk/~sgv/ps/massnurt.ps.g
Identification and prioritisation of sustainability issues for the UK precast concrete industry
As part of its strategy for more sustainable construction, the UK Government has been
encouraging sector representative bodies and trade associations to develop sector
sustainability strategies. A four-year research programme aimed at developing such a
strategy for the precast concrete industry was therefore established by the British Precast
Concrete Federation in 2004, in collaboration with the Department of Civil and Building
Engineering at Loughborough University.
In accordance with best practice, the research began with the identification and prioritisation
of sustainability issues for the precast industry. A facilitated workshop with key practitioners
from the industry identified a series of key business issues for the industry and demonstrated
that sustainability was intrinsically linked to the profitability and competitiveness of the
industry. A questionnaire survey was then conducted to verify and prioritise these issues
across the wider industry. Whilst the survey verified the issues, priorities were found to vary
between groups of companies as a result of them being in different phases of a corporate
sustainability model.
The research has enabled priorities for the precast sector sustainability strategy to be
identified which will facilitate progress towards a more sustainable precast concrete industry
in the UK
The Chlamydia muridarum plasmid revisited : new insights into growth kinetics.
Background: Research in chlamydial genetics is challenging because of its obligate intracellular developmental cycle. In vivo systems exist that allow studies of different aspects of basic biology of chlamydiae, the murine Chlamydia muridarum model is one of great importance and thus an essential research tool. C. muridarum carries a plasmid that has a role in virulence. Our aim was to compare and contrast the C. muridarum plasmid-free phenotype with that of a chromosomally isogenic plasmid-bearing strain, through the inclusion phase of the developmental cycle. Methods: We measured infectivity for plasmid bearing and plasmid-cured C. muridarum by inclusion forming assays in McCoy cells and in parallel bacterial chromosome replication by quantitative PCR, throughout the developmental cycle. In addition to these studies, we have carefully monitored chlamydial inclusion formation by confocal microscopy and transmission electron microscopy. A new E.coli/chlamydial shuttle vector (pNigg::GFP) was constructed using standard cloning technology and used to transform C. muridarum for further phenotypic studies. Results: We have advanced the definition of the chlamydial phenotype away from the simple static observation of mature inclusions and redefined the C. muridarum plasmid-based phenotype on growth profile and inclusion morphology. Our observations on the growth properties of plasmid-cured C. muridarum challenge the established interpretations, especially with regard to inclusion growth kinetics. Introduction of the shuttle plasmid pNigg::GFP into plasmid-cured C. muridarum restored the wild-type plasmid-bearing phenotype and confirmed that loss of the plasmid was the sole cause for the changes in growth and chromosomal replication. Conclusions: Accurate growth curves and sampling at multiple time points throughout the developmental cycle is necessary to define plasmid phenotypes. There are subtle but important (previously unnoticed) differences in the overall growth profile of plasmid-bearing and plasmid-free C. muridarum. We have proven that the differences described are solely due to the plasmid pNigg
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