1,757 research outputs found
Instructional leadership of principals in high performing secondary schools in Cape Town, Western Cape
Includes bibliographical references.The purpose of this research is to examine the extent of instructional leadership of principals in high performing secondary schools in the metropolitan area of Cape Town, Western Cape. A mixed methods design of quantitative and qualitative research was undertaken. For the quantitative phase, the Principal Instructional Management Rating Scale (PIMRS) was administered to 5 principals and 136 teachers. One sample t-tests found statistically significant differences between the mean scores of principals and those of teachers. Data analysis of the PIMRS indicated that principals were most active in protecting instructional time, promoting professional development, providing incentives for learning and framing the school’s goals and least active in supervising and evaluating instruction, maintaining a high visibility and providing incentives for teachers. In the qualitative phase, interviews with the five principals yielded a result that underscores the value which principals place on professional accountability, trusting teachers to deliver the curriculum, building coherence, promoting professional development, giving professional autonomy and fostering relationships. The study found that the principal’s role is multi-faceted and complex and is neither limited to the instructional leadership behaviours of the PIMRS nor to the job description of the Personnel Administration Measures (PAM). Instructional leadership functions not measured by the PIMRS, such as the appointment of teachers, selection of pupils, engaging with stakeholder groups, establishing internal coherence and building trust by sharing instructional leadership practises with senior teachers were very important. School leaders internalize the expectations embedded in accountability systems and have woven these into an internal set of expectations and responsibilities that represent the school’s internal accountability systems. The thesis concludes with the view that both shared leadership and instructional leadership are important as they are indirectly related to pupil achievement
Why compensating fibre nonlinearity will never meet capacity demands
Current research efforts are focussed on overcoming the apparent limits of
communication in single mode optical fibre resulting from distortion due to
fibre nonlinearity. It has been experimentally demonstrated that this Kerr
nonlinearity limit is not a fundamental limit; thus it is pertinent to review
where the fundamental limits of optical communications lie, and direct future
research on this basis. This paper details recently presented results. The work
herein briefly reviews the intrinsic limits of optical communication over
standard single mode optical fibre (SMF), and shows that the empirical limits
of silica fibre power handling and transceiver design both introduce a
practical upper bound to the capacity of communication using SMF, on the order
of 1 Pbit/s. Transmission rates exceeding 1 Pbit/s are shown to be possible,
however, with currently available optical fibres, attempts to transmit beyond
this rate by simply increasing optical power will lead to an asymptotically
zero fractional increase in capacity.Comment: 4 pages, 2 figure
Robustness from flexibility in the fungal circadian clock
Background
Robustness is a central property of living systems, enabling function to be maintained against environmental perturbations. A key challenge is to identify the structures in biological circuits that confer system-level properties such as robustness. Circadian clocks allow organisms to adapt to the predictable changes of the 24-hour day/night cycle by generating endogenous rhythms that can be entrained to the external cycle. In all organisms, the clock circuits typically comprise multiple interlocked feedback loops controlling the rhythmic expression of key genes. Previously, we showed that such architectures increase the flexibility of the clock's rhythmic behaviour. We now test the relationship between flexibility and robustness, using a mathematical model of the circuit controlling conidiation in the fungus Neurospora crassa.
Results
The circuit modelled in this work consists of a central negative feedback loop, in which the frequency (frq) gene inhibits its transcriptional activator white collar-1 (wc-1), interlocked with a positive feedback loop in which FRQ protein upregulates WC-1 production. Importantly, our model reproduces the observed entrainment of this circuit under light/dark cycles with varying photoperiod and cycle duration. Our simulations show that whilst the level of frq mRNA is driven directly by the light input, the falling phase of FRQ protein, a molecular correlate of conidiation, maintains a constant phase that is uncoupled from the times of dawn and dusk. The model predicts the behaviour of mutants that uncouple WC-1 production from FRQ's positive feedback, and shows that the positive loop enhances the buffering of conidiation phase against seasonal photoperiod changes. This property is quantified using Kitano's measure for the overall robustness of a regulated system output. Further analysis demonstrates that this functional robustness is a consequence of the greater evolutionary flexibility conferred on the circuit by the interlocking loop structure.
Conclusions
Our model shows that the behaviour of the fungal clock in light-dark cycles can be accounted for by a transcription-translation feedback model of the central FRQ-WC oscillator. More generally, we provide an example of a biological circuit in which greater flexibility yields improved robustness, while also introducing novel sensitivity analysis techniques applicable to a broader range of cellular oscillators
The generation of an induced pluripotent stem cell line (DCGi001-A) from an individual with FOXG1 syndrome carrying the c.460dupG (p.Glu154fs) variation in the FOXG1 gene
FOXG1 syndrome is a neurodevelopmental disorder caused by mutations in the FOXG1 gene. Here, an induced pluripotent stem cell (iPSC) line was generated from human dermal fibroblasts of an individual with the c.490dupG (p.Glu154fs) mutation in the FOXG1 gene. Fibroblasts were reprogrammed using non-integrating episomal plasmids and pluripotency marker expression was confirmed by both immunocytochemistry and quantitative PCR in the resultant iPSC line. There were no karyotypic abnormalities and the cell line successfully differentiated into all three germ layers. This cell line may prove useful in the study of the pathogenic mechanisms that underpin FOXG1 syndrome
Molecular Carbon Chains and Rings in TMC-1
We present mapping results in several rotational transitions of HC3N, C6H,
both cyclic and linear C3H2 and C3H, towards the cyanopolyyne peak of the
filamentary dense cloud TMC-1 using the IRAM 30m and MPIfR 100m telescopes. The
spatial distribution of the cumulene carbon chain propadienylidene H2C3
(hereafter l-C3H2) is found to deviate significantly from the distributions of
the cyclic isomer c-C3H2, HC3N, and C6H which in turn look very similar. The
cyclic over linear abundance ratio of C3H2 increases by a factor of 3 across
the filament, with a value of 28 at the cyanopolyyne peak. This abundance ratio
is an order of magnitude larger than the range (3 to 5) we observed in the
diffuse interstellar medium. The cyclic over linear abundance ratio of C3H also
varies by ~2.5 in TMC-1, reaching a maximum value (13) close to the
cyanopolyyne peak. These behaviors might be related to competitive processes
between ion-neutral and neutral-neutral reactions for cyclic and linear
species.Comment: Accepted for publication in The Astrophysical Journal, part I. 24
pages, including 4 tables, 7 figures, and figure caption
Axion detection with phonon-polaritons revisited
In the presence of a background magnetic field, axion dark matter induces an
electric field and can thus excite phonon-polaritons in suitable materials. We
revisit the calculation of the axion-photon conversion power output from such
materials, accounting for finite volume effects, and material losses. Our
calculation shows how phonon-polaritons can be converted to propagating photons
at the material boundary, offering a route to detecting the signal. Using the
dielectric functions of GaAs, AlO, and SiO, a fit to our loss model
leads to a signal of lower magnitude than previous calculations. We demonstrate
how knowledge of resonances in the dielectric function can directly be used to
calculate the sensitivity of any material to axion dark matter. We argue that a
combination of low losses encountered at K temperatures and
near future improvements in detector dark count allow one to probe the QCD
axion in the mass range meV. This provides further impetus to
examine novel materials and further develop detectors in the THz regime. We
also discuss possible tuning methods to scan the axion mass.Comment: 13 pages, 2 figures, 1 table, comments welcom
Reflections on the 1976 Swine Flu Vaccination Program
The swine flu vaccination program has implications for the current pandemic preparedness
The distribution of H13CN in the circumstellar envelope around IRC+10216
H13CN J=8-7 sub-millimetre line emission produced in the circumstellar
envelope around the extreme carbon star IRC+10216 has been imaged at
sub-arcsecond angular resolution using the SMA. Supplemented by a detailed
excitation analysis the average fractional abundance of H13CN in the inner wind
(< 5E15 cm) is estimated to be about 4E-7, translating into a total HCN
fractional abundance of 2E-5 using the isotopic ratio 12C/13C=50.
Multi-transitional single-dish observations further requires the H13CN
fractional abundance to remain more or less constant in the envelope out to a
radius of about 4E16 cm, where the HCN molecules are effectively destroyed,
most probably, by photodissociation. The large amount of HCN present in the
inner wind provides effective line cooling that can dominate over that
generated from CO line emission. It is also shown that great care needs to be
taken in the radiative transfer modelling where non-local, and non-LTE, effects
are important and where the radiation field from thermal dust grains plays a
major role in exciting the HCN molecules. The amount of HCN present in the
circumstellar envelope around IRC+10216 is consistent with predicted
photospheric values based on equilibrium chemical models and indicates that any
non-equilibrium chemistry occurring in the extended pulsating atmosphere has no
drastic net effect on the fractional abundance of HCN molecules that enters the
outer envelope. It further suggests that few HCN molecules are incorporated
into dust grains.Comment: Accepted for publication in ApJ. 20 pages, 7 figure
Epidemiology of glenohumeral dislocation and subsequent instability in an urban population
Background: Glenohumeral dislocation is the most commonly encountered adult joint instability. The epidemiology
in the United Kingdom and worldwide is unclear and often limited to young, active groups
that are not representative of general populations. Information regarding epidemiology and outcome from
a first dislocation is useful for trauma service planning and patient counseling. We calculated the incidence
of shoulder instability after a first dislocation in our urban population and investigated predictors
of recurrent instability.
Methods: A prospectively collected trauma database was retrospectively examined to identify patients with
a first-time dislocation. Demographics, subsequent dislocation, and instability details were collected from
electronic patient records.
Results: In a 38-month study period, 329 first dislocations occurred in a population of 475,147 with mean
follow-up 28.5 months (range, 10-50 months). The overall incidence for first-time dislocations in this population
was 21.9 per 100,000 population, of which 7.9% sustained a redislocation and 6.1% had further
symptomatic instability. There were 18.8% with associated greater tuberosity fractures, 8.8% sustained a
nerve injury, and 2.7% were posterior dislocations. A bimodal distribution was observed for males (peak
incidence per 100,000 of 42.1 and 50.9 in 15-24 and ≥85 age groups, respectively), and unimodal for females
(peak 45.7 in the 65-74 age group).
Conclusion: We demonstrate a previously unreported burden of dislocation in older age groups and suggest
a rate of recurrence lower than previously reported in the United Kingdom. The group aged 15 to 19 years
was at the highest risk of recurrent dislocation and instability. Gender was not a significant predictor of instability
Transient Radio Lines from Axion Miniclusters and Axion Stars
Gravitationally bound clumps of dark matter axions in the form of
'miniclusters' or even denser 'axion stars' can generate strong radio signals
through axion-photon conversion when encountering highly magnetised neutron
star magnetospheres. We systematically study encounters of axion clumps with
neutron stars and characterise the axion infall, conversion and the subsequent
propagation of the photons. We show that the high density and low escape
velocity of the axion clumps lead to strong, narrow, and temporally
characteristic transient radio lines with an expected duration varying from
seconds to months. Our work comprises the first end-to-end modeling pipeline
capable of characterizing the radio signal generated during these transient
encounters, quantifying the typical brightness, anisotropy, spectral width, and
temporal evolution of the radio flux. The methods developed here may prove
essential in developing dedicated radio searches for transient radio lines
arising from miniclusters and axion stars.Comment: v2: Minor updates made to match published version. v1: 17 pages, 15
figure
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