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A tale of one city: intra-institutional variations in migrating VLE platform
City University London committed in 2009 to make Moodle the Virtual Learning Environment (VLE) at the core of a new Strategic Learning Environment (SLE) comprised of VLE, externally facing website and related systems such as video streaming and virtual classrooms. Previously, the WebCT VLE had been separate from most of the other systems at the institution with very limited connections to other tools. Each of the schools within the institution was able to pursue their own strategy and timeframe for the migration and embedding of Moodle within their subject areas, within an absolute limit of 2 years. This paper outlines the approaches taken by the various schools, highlighting similarities and differences, and draws out common aspects from the project to make recommendations for institutions seeking to undertake similar migrations
How an improved implementation of H2 self-shielding influences the formation of massive stars and black holes
High redshift quasars at z>6 have masses up to ~ M. One of the
pathways to their formation includes direct collapse of gas, forming a
supermassive star, precursor of the black hole seed. The conditions for direct
collapse are more easily achievable in metal-free haloes, where atomic hydrogen
cooling operates and molecular hydrogen (H2) formation is inhibited by a strong
external UV flux. Above a certain value of UV flux (J_crit), the gas in a halo
collapses isothermally at ~ K and provides the conditions for
supermassive star formation. However, H2 can self-shield, reducing the effect
of photodissociation. So far, most numerical studies used the local Jeans
length to calculate the column densities for self-shielding. We implement an
improved method for the determination of column densities in 3D simulations and
analyse its effect on the value of J_crit. This new method captures the gas
geometry and velocity field and enables us to properly determine the
direction-dependent self-shielding factor of H2 against photodissociating
radiation. We find a value of J_crit that is a factor of two smaller than with
the Jeans approach (~2000 J_21 vs. ~4000 J_21). The main reason for this
difference is the strong directional dependence of the H2 column density. With
this lower value of J_crit, the number of haloes exposed to a flux >J_crit is
larger by more than an order of magnitude compared to previous studies. This
may translate into a similar enhancement in the predicted number density of
black hole seeds.Comment: 14 pages, 12 figures, published in MNRA
NAO und Vorhersagbarkeit / NAO and predictability
Ein Überblick über die Güte heutiger NAO-Vorhersagen und Vorhersagbarkeit der NAO an sich wird gegeben.
Der Einfluss der wesentlichen Prozesse auf die Vorhersagegüte auf saisonal-interannualen und dekadischen Zeitskalen
wird zusammengetragen. Auf den saisonal-interannualen Zeitskalen ist vor allem die Wärmekapazität und
der Wärmetransport der oberen Schichten des Nordatlantik von Bedeutung für den Anstieg der NAO-Vorhersagegüte.
Statistische Modelle sowie gekoppelte Atmosphäre-Ozean-Ensemble-Vorhersagesysteme weisen für die
beiden letzten Dekaden des 20 Jahrhunderts eine Vorhersagegüte von etwa 15 % auf. Die Vorhersagegüte über die
letzten 50 Jahre liegt jedoch unter 10 %. Auf dekadischen Zeitskalen bildet die atlantische meridionale Umwälzbewegung
eine Grundlage für die Vorhersagen des dekadischen Klimas in der atlantischen Region.
A review of the NAO prediction and predictability is given. The impact of basic processes governing the NAO variability
and their feasibility to enhance prediction skill on seasonal-to-interannual and decadal timescales is investigated.
On seasonal-to-interannual timescales heat content and transport of the North Atlantic upper layer ocean
can be essential to increase winter NAO prediction skill. Statistical models and coupled atmosphere-ocean ensemble
prediction systems suggest a positive skill of about 15% for the latest decades in the 20th century. The prediction
skill for the last 50 years, however, is below 10%. On decadal timescales particularly the meridional overturning
circulation provides the basis for forecasts of the decadal climate over the North Atlantic region
Effects of turbulence and rotation on protostar formation as a precursor to seed black holes
Context. The seeds of the first supermassive black holes may have resulted
from the direct collapse of hot primordial gas in K haloes,
forming a supermassive or quasistar as an intermediate stage.
Aims. We explore the formation of a protostar resulting from the collapse of
primordial gas in the presence of a strong Lyman-Werner radiation background.
Particularly, we investigate the impact of turbulence and rotation on the
fragmentation behaviour of the gas cloud. We accomplish this goal by varying
the initial turbulent and rotational velocities.
Methods. We performed 3D adaptive mesh refinement simulations with a
resolution of 64 cells per Jeans length using the ENZO code, simulating the
formation of a protostar up to unprecedentedly high central densities of
cm, and spatial scales of a few solar radii. To achieve this
goal, we employed the KROME package to improve modelling of the chemical and
thermal processes.
Results. We find that the physical properties of the simulated gas clouds
become similar on small scales, irrespective of the initial amount of
turbulence and rotation. After the highest level of refinement was reached, the
simulations have been evolved for an additional ~5 freefall times. A single
bound clump with a radius of AU and a mass of ~ M is formed at the end of each simulation, marking the onset
of protostar formation. No strong fragmentation is observed by the end of the
simulations, regardless of the initial amount of turbulence or rotation, and
high accretion rates of a few solar masses per year are found.
Conclusions. Given such high accretion rates, a quasistar of
M is expected to form within years.Comment: 18 pages, 7 figures, fixed typos, added references and clarified some
details; accepted for publication in A&
Extraction of biological hydroxyapatite from tuna fish bone for biomedical applications
Natural hydroxyapatite (HAp) is known for its common use in biomedical applications including in orthopaedic and implantation. HAp can be extracted from natural resources such as eggshells, fish bones and coral. Annually, it is found that huge amount of tuna fish bones was thrown away and being wasted as results from great consumption of tuna fish. In this study, tuna fish bones were extracted and characterised to be used in biomedical applications. Specifically, tuna fish bones were cleaned, and calcined at high temperature of 700 °C, 900 °C and 1100 °C. Powders
calcined at 700 °C showed pure HAp compared to powders calcined at 900 °C and 1100 °C which showed the presence of β-TCP. As temperature rising, the morphology of the powders also changes
from spherical-shaped to irregular-shaped indicated the substitution of phosphate and calcium from the β-TCP which also influenced the ratio of Ca/P obtained. In this study, powders calcined at 700 °C obtained optimum Ca/P ratio of 1.60. Moreover, EDS analysis showed the presence of tracer elements such as Ca, Mg, Sr Na, K and Zn in all calcined samples. These elements can help improve the biocompatibility of the HAp and beneficial for biomedical applications
A UV flux constraint on the formation of direct collapse black holes
The ability of metal free gas to cool by molecular hydrogen in primordial
halos is strongly associated with the strength of ultraviolet (UV) flux
produced by the stellar populations in the first galaxies. Depending on the
stellar spectrum, these UV photons can either dissociate molecules
directly or indirectly by photo-detachment of as the latter
provides the main pathway for formation in the early universe. In
this study, we aim to determine the critical strength of the UV flux above
which the formation of molecular hydrogen remains suppressed for a sample of
five distinct halos at by employing a higher order chemical solver and a
Jeans resolution of 32 cells. We presume that such flux is emitted by PopII
stars implying atmospheric temperatures of ~K. We performed
three-dimensional cosmological simulations and varied the strength of the UV
flux below the Lyman limit in units of . Our findings show that the
value of varies from halo to halo and is sensitive to the
local thermal conditions of the gas. For the simulated halos it varies from
400-700 with the exception of one halo where .
This has important implications for the formation of direct collapse black
holes and their estimated population at z > 6. It reduces the number density of
direct collapse black holes by almost three orders of magnitude compared to the
previous estimates.Comment: 10 pages, 6 figures, matches the accepted version to ber published in
MNRAS, higher resolution version is available at
http://www.astro.physik.uni-goettingen.de/~mlatif/Jcrit.pd
Evaluasi Aspek Keselamatan Kegiatan Metalografi Di Instalasi Elemen Bakar Eksperimental
─Telah dilakukan evaluasi aspek keselamatan kegiatan metalografi di Instalasi Elemen Bakar Eksperimental. Tujuan dari kegiatan ini untuk mengetahui aspek keselamatan dari kegiatan metalografi di IEBE. Pengukuran kontaminasi dilakukan terhadap meja preparasi, peralatan metalografi yang berpotensi terkontaminasi, kemudian penanganan limbah cair dan padat serta pelaksanaan dekontaminasi pada meja kerja preparasi, atau lokasi penempatan sampel hasil metalografi. Hasil pengukuran pada titik pantau yang variatif, didapatkan hasil yang tertinggi yaitu pada titik pantau 1, lebih tinggi dari titik pengukuran yang lain. Dari hasil rata-rata pada titik pantau 1 (satu) didapatkan hasil pengukuran (0,245 ± 0,014 Bq/cm2), sedangkan pada titik pantau 2 (dua) didapat hasil pengukuran (0,228 ± 0,008 Bq/cm2), titik pengukuran 3 (tiga) didapat hasil pengukuran (0,238 ± 0,006550 Bq/cm2)dan titik pantau 4 (empat) didapatkan hasil pengukuran (0,232 ± 0,035 Bq/cm2). Pengukuran tingkat kontaminasi pasca deko pada titik pantau 1 didapat rata-rata 0,245 ± 0,014 Bq/cm2. Pasca dekontaminasi kontaminasi dapat diturunkan menjadi 0,018 ± 0,007 Bq/cm2. Pengukuran kontaminasi juga dilakukan pada peralatan metalografi dan didapatkan hasil pengukuran terendah 0,049 Bq/cm2, sedangkan tertinggi 0,059 Bq/cm2 dengan rata-rata 0,054 ± 0,005 Bq/cm2 Sedangkan pada titik pantau lainnya lebih rendah. Dari kegiatan metalografi ini dipastikan dapat menghasilkan dua jenis limbah baik limbah padat maupun limbah cair. Dari hasil limbah padat yang didapatkan akan ditampung pada wadah limbah yang tersedia, sedangkan untuk limbah cair dilakukan analisa kandungan uraniumnya, apabila terdapat kandungan uranium lebih besar 50 ppm maka akan dilakukan pemungutan kembali. Secara keseluruhan kegiatan metalografi di IEBE sudah terpenuhi dari aspek keselamatan dan tidak menyimpang dari kaidah dan norma keselamatan yang ada
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