5,149 research outputs found
Positron Tunnelling through the Coulomb Barrier of Superheavy Nuclei
We study beams of medium-energy electrons and positrons which obey the Dirac
equation and scatter from nuclei with At small distances the
potential is modelled to be that of a charged sphere. A large peak is found in
the probability of positron penetration to the origin for This
may be understood as an example of Klein tunnelling through the Coulomb
barrier: it is the analogue of the Klein Paradox for the Coulomb potential.Comment: 3 figures, to be published in Physics Letters
Probing the distance and morphology of the Large Magellanic Cloud with RR Lyrae stars
We present a Bayesian analysis of the distances to 15,040 Large Magellanic
Cloud (LMC) RR Lyrae stars using - and -band light curves from the
Optical Gravitational Lensing Experiment, in combination with new -band
observations from the Dark Energy Camera. Our median individual RR Lyrae
distance statistical error is 1.89 kpc (fractional distance error of 3.76 per
cent). We present three-dimensional contour plots of the number density of LMC
RR Lyrae stars and measure a distance to the core LMC RR Lyrae centre of
,
equivalently . This finding is statistically consistent with and four
times more precise than the canonical value determined by a recent
meta-analysis of 233 separate LMC distance determinations. We also measure a
maximum tilt angle of at a position angle of
, and report highly precise constraints on the , , and RR
Lyrae period--magnitude relations. The full dataset of observed mean-flux
magnitudes, derived colour excess values, and fitted distances for
the 15,040 RR Lyrae stars produced through this work is made available through
the publication's associated online data.Comment: 7 pages, 8 figure
STUDENTSâ PERCEPTION OF ONLINE GROSS ANATOMY LABORATORY CLASSES VIA ZOOM TECHNOLOGY
BACKGROUND
During the 1st semester of 2020 the unit âFunctional Anatomy of the Trunkâ was re-designed and taught online, in response to the COVID-19 virus lockdown.
AIMS
The aim of this study was to investigate whether the use of computer based online support tools (as replacement of the traditional cadaver based laboratory learning), in conjunction with a focused period of synchronous Zoom delivery, achieved student outcomes and learning experience.
DESCRIPTION OF INTERVENTION
The curriculum of the unit deals with the gross anatomy of the human trunk. The unit was taught in small groups (around 30 students) and entirely online with Zoom technology.
DESIGN AND METHODS
N=41 first year students participated in this study and were invited at the conclusion of the unit to complete an anonymous opinion-based survey (via Qualtrics). Student grades and learning management system analytics was also analysed.
RESULTS
Preliminary results indicate that studentsâ perception of the online gross anatomy laboratory learning was positive and extended their learning. However, the online learning platform has its limitations, not using real bodies makes it harder to appreciate the 3D relationships between structure and function.
CONCLUSIONS
Studentsâ perception of online learning as a replacement of the traditional gross anatomy laboratory was surprisingly positive. Most agreed that it provided valuable insights and improved their understanding of anatomy as well as helped with the application of anatomical knowledge. Equally so, they strongly agreed that the online 2D learning experience was less engaging and interesting than learning using real bodies
Long-term musculoskeletal morbidity after adult burn injury: a population-based cohort study
Objective - To investigate if adults who are hospitalised for a burn injury have increased long-term hospital use for musculoskeletal diseases. Design - A population-based retrospective cohort study using linked administrative health data from the Western Australian Data Linkage System. Subjects - Records of 17,753 persons aged at least 20 years when hospitalised for a first burn injury in Western Australia during the period 1980â2012, and 70,758 persons who were age and gender-frequency matched with no injury admissions randomly selected from Western Australia's electoral roll. Main outcome measures - Admission rates and cumulative length of stay for musculoskeletal diseases. Negative binomial and Cox proportional hazards regression modelling were used to generate incidence rate ratios (IRR) and HRs with 95% CIs, respectively. Results - After adjustment for pre-existing health status and demographic characteristics, the burn cohort had almost twice the hospitalisation rate for a musculoskeletal condition (IRR, 95% CI 1.98, 1.86 to 2.10), and spent 3.70 times as long in hospital with a musculoskeletal diagnosis (95% CI 3.10 to 4.42) over the 33-year period, than the uninjured comparison cohort. Adjusted survival analyses of incident post-burn musculoskeletal disease admissions found significant increases for the 15-year post burn discharge period (0â6 months: HR, 95% CI 2.51, 2.04 to 3.11; 6 monthsâ2 years: HR, 95% CI 1.77, 1.53 to 2.05; 2â15 years: HR, 95% CI 1.32, 1.23 to 1.42). Incident admission rates were significantly elevated for 20 years post-burn for minor and severe burn injury for a range of musculoskeletal diseases that included arthropathies, dorsopathies, osteopathies and soft tissue disorders. Conclusions - Minor and severe burn injuries were associated with significantly increased post-burn incident admission rates, long-term hospital use and prolonged length of stay for a range of musculoskeletal diseases. Further research is required that facilitates identification of at-risk patients and appropriate treatment pathways, to reduce the long-term morbidity associated with burns
Engineering of Cyclodextrin Product Specificity and pH Optima of the Thermostable Cyclodextrin Glycosyltransferase from Thermoanaerobacterium thermosulfurigenes EM1
The product specificity and pH optimum of the thermostable cyclodextrin glycosyltransferase (CGTase) from Thermoanaerobacterium thermosulfurigenes EM1 was engineered using a combination of x-ray crystallography and site-directed mutagenesis. Previously, a crystal soaking experiment with the Bacillus circulans strain 251 ÎČ-CGTase had revealed a maltononaose inhibitor bound to the enzyme in an extended conformation. An identical experiment with the CGTase from T. thermosulfurigenes EM1 resulted in a 2.6-Ă
resolution x-ray structure of a complex with a maltohexaose inhibitor, bound in a different conformation. We hypothesize that the new maltohexaose conformation is related to the enhanced α-cyclodextrin production of the CGTase.
The detailed structural information subsequently allowed engineering of the cyclodextrin product specificity of the CGTase from T. thermosulfurigenes EM1 by site-directed mutagenesis. Mutation D371R was aimed at hindering the maltohexaose conformation and resulted in enhanced production of larger size cyclodextrins (ÎČ- and Îł-CD). Mutation D197H was aimed at stabilization of the new maltohexaose conformation and resulted in increased production of α-CD.
Glu258 is involved in catalysis in CGTases as well as α-amylases, and is the proton donor in the first step of the cyclization reaction. Amino acids close to Glu258 in the CGTase from T. thermosulfurigenes EM1 were changed. Phe284 was replaced by Lys and Asn327 by Asp. The mutants showed changes in both the high and low pH slopes of the optimum curve for cyclization and hydrolysis when compared with the wild-type enzyme. This suggests that the pH optimum curve of CGTase is determined only by residue Glu258.
Centaurus A: multiple outbursts or bursting bubble?
We present new radio observations of the brighter region of the northern lobe
(the Northern Middle Lobe, NML) of Centaurus A obtained at 20 cm with the
Australia Telescope Compact Array. The angular resolutions are ~50 and ~130
arcsec, therefore much higher than for the previously available radio images of
this region. The most interesting feature detected is a large-scale jet that
connects the inner radio lobe and the NML and that is imaged for the first
time. The NML itself appears as diffuse emission with a relatively bright ridge
on the eastern side. The radio morphology of Centaurus A and, in particular,
its NML could be the result of a precessing jet that has undergone a strong
interaction with the environment at least in the northern side. The very big
drop in intensity between the inner jet and the large-scale jet can be
explained with a sequence of bursts of activity at different epochs in the life
of the source. Alternatively (or additionally) a ``bursting bubble'' model is
proposed which could also explain the good collimation of the large-scale jet.
In this model, the plasma accumulated in the inner lobe would be able to
``burst'' out only through one nozzle that would be the region where the
large-scale jet forms. From the comparison between the radio emission and the
regions of ionized gas we find that the inner optical filament falls about 2
arcmin (~2 kpc) away from the large-scale radio jet. Thus, this filament does
not seem to have experienced a direct interaction with the radio plasma. The
outer filaments appear to be, in projection, closer to the radio emission,
arguing for a direct interaction with the radio jet. However, also in this case
a more complicated interaction than assumed so far has to be occuring.Comment: To appear in MNRAS; 11 pages, LateX, 7 figures. Fig 1 is available at
http://www.ira.bo.cnr.it/~rmorgant/Centaurus
Low Momentum Scattering in the Dirac Equation
It is shown that the amplitude for reflection of a Dirac particle with
arbitrarily low momentum incident on a potential of finite range is -1 and
hence the transmission coefficient T=0 in general. If however the potential
supports a half-bound state at k=0 this result does not hold. In the case of an
asymmetric potential the transmission coefficient T will be non-zero whilst for
a symmetric potential T=1.Comment: 12 pages; revised to include additional references; to be published
in J Phys
The Multidimensional Study of Viral Campaigns as Branching Processes
Viral campaigns on the Internet may follow variety of models, depending on
the content, incentives, personal attitudes of sender and recipient to the
content and other factors. Due to the fact that the knowledge of the campaign
specifics is essential for the campaign managers, researchers are constantly
evaluating models and real-world data. The goal of this article is to present
the new knowledge obtained from studying two viral campaigns that took place in
a virtual world which followed the branching process. The results show that it
is possible to reduce the time needed to estimate the model parameters of the
campaign and, moreover, some important aspects of time-generations relationship
are presented.Comment: In proceedings of the 4th International Conference on Social
Informatics, SocInfo 201
Enhancing Student Success: Developing and Evaluating an Effective Advice and Guidance Consultation System
The objective of this study was to create and evaluate an advice and guidance consultation system for a learning institution in Nueva Ecija, Philippines. The study employed a developmental research design and involved IT experts and end-users from various senior high school tracks as respondents, who were selected using purposive sampling. The system was developed based on the software development life cycle model, and its technical aspects and quality were evaluated using ISO 25010 software standards. The results indicated that the system was well-received by end-users and met their needs and expectations. The study recommends following the SDLC model, conducting regular assessments, and continuing to improve the system. The study highlights the importance of a systematic approach to system development and the significance of assessing the technical aspects and quality of use of the system. The findings can serve as a foundation for future studies on the development and evaluation of comparable systems
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