995 research outputs found
From theoretical stellar spectra to realistic models of the Milky Way : a never ending Odyssey
No full textThe last chapter is dedicated to the compilation of the results and the discussion about the success of - but also
about the problems that have arisen during - and in part also survived - this work.
The main goal of this thesis was, firstly, to convert the stellar parameters given by galaxy models into observables,
and then to compare these theoretical stellar distributions in different viewing directions with real observational
data to check, if it is possible to find a best-fitting galaxy model for our MilkyWay.
To do so, we transformed the physical parameters, i.e. the stellar mass, current age and constant chemical
abundance of each star in a certain viewing direction and field size, given by ten different, detailed galaxy models
that were computed with the 3D chemo-dynamical code of Samland, Hensler & Theis (1997) and Samland &
Gerhard (2003) into observable absolute and apparent magnitudes and colours.
For each star, we used its stellar mass, age and chemical abundance to select the corresponding evolutionary
track from the stellar evolutionary track library, Padova 1994, computed by Bressan et al. (1993), Fagotto et
al. (1994a, 1994b, 1994c) and Girardi et al. (1996), to derive the appropriate stellar atmospheric parameters (i.e.,
log g and Te�).
Using stellar metallicity, effective temperature and surface gravity, we interpolate an appropriate spectral energy
distribution provided by synthetic stellar spectral libraries, BaSeL 3.2 or PHOENIX, and in connection with
the response filter functions of various photometric filter systems (e. g., RGU and ugriz) for observable magnitudes
and colours for each star.
By means of the spectrophotometric data we compile synthetic colour-magnitude diagrams, and age- and metallicity
distributions for a number of viewing directions and field sizes. These theoretical data are then compared
to the photometric field star observations from both the Basel and the Sloan Digital Sky Surveys.
Our intention is to first compare the differences between our suite of models and observations, so as to
identify the correlations between the observed data and the input parameters of our models. In a next step we
want to fine-tune the model parameters to fit the Basel and/or SDSS survey data and thereby to find the best-fitting
galaxy model for our MilkyWay.
Unfortunately, the fine-tuning of the model galaxy parameters has not been possible1 - which forced us to
limit our analysis to only 10 different models without any further adjustments.
6.1. Success
Before starting our comparison of theoretical with observational data, we complete the BaSeL 3.1 (Westera
2001; Westera et al. 2002)- and the PHOENIX (Hauschildt & Baron 1999, 2004) stellar spectral libraries by
implementing a grid of theoretical white dwarf stellar spectra covering high surface gravities (log g > 5.0) and
high effective temperatures (50’000 K � Te� � 100’000 K) calculated by Koester (2004). Similarly, we also
include hot central star spectra of planetary nebulae computed by Rauch (2003) that cover a temperature range
of 100’000 � Te� � 1’000’000 K and surface gravities of 5.0 � log g � 9.0.
Finally, we end up with a useful tool for reproducing stellar data of various stellar types on different photometric
systems, such as RGU and SDSS. By means of these theoretical spectral libraries the interpretation of any stellar
data (e.g., SDSS SEGUE proprietary data) in terms of physical stellar parameters is highly warranted.
As mentioned above, for our comparison we only have ten model galaxies available. Out of these ten, we
find the best-fitting model galaxy to be the spiral model galaxy S10, described in detail in Subsection 3.2.2.
During our work of comparison we gained deeper insights into all the different fields of work that are involved
in the conversion of the model data into observables. The major ingredients of this study are highlighted
in blue in the previous paragraph:
stellar evolutionary models, stellar atmosphere models,
photometric system parameters, and last, but not least:
the chemo-dynamical galaxy models themselves .
Beside the fact, that gathering and comprehending the actual knowledge of all of them is a great challenge,
the coin also has another side: each field of work still has some unknown or untested parts and therefore brings
its own, sometimes inestimable, uncertainties with it.
We track down several inconsistencies in the above-mentioned ingredients and discuss them in due detail in the
present work.
In future work, we suggest that appropriate corrections be applied, before making further and unbiased
comparisons. In the next Sections, we enlist the major inconsistencies between the surveys, spectral libraries and
between synthetic and observed SDSS colours and propose possible future scientific projects.
6.2. Problems and uncertainties
6.2.1. Chemo-dynamical galaxy model
Westera et al. (2002) showed that the bulge colours derived from disk galaxy formation models of Samland &
Gerhard (2003) agree very well with Hubble Deep Field North bulge colours. In our case, where we are immersed
in a galaxy model and compare its spatial stellar distributions and luminosity functions with the much
more detailed substructures of our own Galaxy, no such good agreement can be found.
The validity of any galactic model is always questionable, as it describes a smooth and in the case of the Samland
models an axially symmetric galaxy, while in our days we know through observations that inhomogeneities exist
even in the disk or in the halo.
Thanks to the increasing computational power, we are able to simulate the formation and evolution of a disk
galaxy in three-dimensional numerical models, including the most important physical processes. But even in our
days, the computational power has its limits. Therefore, it is not possible to account for all the processes acting
from the atomic to the galactic scales.
In the Samland code, the stellar particles are created and distributed according to the star formation. The restriction
to the fundamental processes, which determine the galactic evolution, may affect the detailed shape of the
star formation history. Too many important details influence the formation and evolution of a model star that
affect the stellar radiative properties and spatial distributions in a crucial way, which exceeds by far the error bars
of the empirical calibrations of the local luminosity functions.
Beside these general problems of simulating complex interactions, the Samland code revealed additional artefacts,
as we have seen for example in Subsection 5.1.2. Unfortunately, the easily implementable adjustments to
the code are not possible anymore, as mentioned above.
6.2.2. Stellar evolutionary tracks and synthetic photometry
Stellar evolutionary tracks
Even though the stellar evolutionary models are increasingly sophisticated, with improved physics, various uncertainties
still lie in the description of the details in the shape of stellar evolutionary tracks, and the evolutionary
lifetimes. Here we just mention some of them: Core convection, mass loss, mixing length, rotation, diffusion,
meridional circulation, and nuclear reactions.
Additionally, the complete set of evolutionary tracks of the Padova94 library does not include the TP-AGB nor
the post-AGB phase. On account of this we adopted the enhancements of Bruzual & Charlot (2003) that consist
only of simplified descriptions of these phases.
Spectral libraries
In addition, we have shown that the two theoretical stellar spectral libraries, BaSeL 3.2 and PHOENIX, do not
provide matching synthetic colours throughout the full parameter ranges. The largest differences between the
two stellar spectral libraries show up in almost all colours at lower effective temperatures (3’500 � Te� ) and
higher surface gravities (2.5 � log g) (see A.1).
Due to the bright limiting apparent magnitudes that we apply to produce model colours under the same conditions
as the observed colours, these uncertainties do not affect our work that much. Still, the (small) contribution of
such stars that are not yet sufficiently tested is difficult to estimate and their impacts on the stellar radiative
properties not yet definitely determined.
Filter functions
The comparison of the SDSS survey- with the model star counts reveals a satisfying agreement in the u-gcolour.
Unfortunately, other colours do not show the same result, and therefore lead us to analyse the SDSS
colours more deeply.
The comparison of theoretical and observed stellar distributions in the i-z versus r-i- plane (see 5.2) demonstrates
impressively, that the observed two-colour distribution can not be reproduced by synthetic colours of any
theoretical stars. Only synthetic colours transformed from the Johnson-Cousins system (Jordi, Grebel & Ammon
2005) follow the i-z versus r-i colour relation of the observed stars correctly.
By contrast, the transformed synthetic model and the observed stars in the g-r versus u-g- plane fit well.
The conclusion appears inevitable that three published SDSS filter functions (r, i and z) do not match the observational
system, and are therefore responsible for this deviation.
6.2.3. Observational data
The comparison of the Basel survey with our model galaxies reveals large inadjustable inconsistencies in star
counts in all the available viewing directions. We therefore include checks on SDSS data and compare the apparent
magnitude histograms of stars in common fields.
A comparison of the Basel- with the Sloan Digital Sky Survey uncovers unexpected large systematic deviations
between the apparent magnitude histograms in the magnitude range that is common to both surveys.
The higher resolution of the SDSS CCD photometry compared with the one of the Basel survey can only partly
explain the differences of these two surveys. By comparing three fields that both surveys have in common, Jordi,
Grebel & Ammon (2005) discovered uncertainties concerning the identification of some of the observed objects:
Some objects recognised by the Sloan Digital Sky Survey as galaxies are treated as stars in the Basel survey. In
other cases, the SDSS detector simply did not observe a star, whereas the Basel survey detected one. Occasionally
the SDSS detected a fainter object within a radius of 1" to 3" of the dominant star, whereas Basel detected
only one single source. Around 10 % of the Basel stars are not identified in the SDSS catalogue as single stars.
In our work we compare (assumed) observed single stars with single model stars. If a survey classifies galaxies
or the like as single stars, the whole stellar spatial distribution gets affected.
Furhermore, the SDSS survey has a saturation cutoff at the apparent magnitude of r ~ 14.0, which means that the
images of all stars brighter than this magnitude contain saturated pixels and that their photometry is questionable.
Another uncertainty of the SDSS DR3 are quasars which have not yet been separated. And, as we showed in
Subsection 5.2, a satisfactory algorithm to unambiguously identify and exclude all quasars from a mixed stellar
sample does not exist. But all this is not a final explanation, why these two surveys end up with different star
numbers.
Of course, such mismatches between the two surveys do not allow a definite validation of the model.
Because of all these still considerable inconsistencies and uncertainties accompanying the use of the major ingredients
(stellar evolutionary models of Padova, stellar atmosphere models of the BaSeL 3.2 and the PHOENIX
library, photometric system parameters, such as the SDSS filter functions, and last but not least: the chemodynamical
model galaxies) mentioned above, we are unable - unfortunately - to draw final conclusions about
the validity of the Samland models, or to find a unique best-fitting solution for the Milky Way
The septin cytoskeleton is associated with distinct myelin structures of the central and peripheral nervous system
No full textRapid conduction of nerve impulses in the nervous system of higher vertebrates is made possible by ensheathment of nerve fibers by the specialized plasma membrane structure myelin. Consequently, failure of myelination or damage to the myelin sheath leads to severe pathology as seen in multiple sclerosis. During myelination oligodendrocytes and Schwann cells are challenged to build up and maintain a highly complex multilaminar plasma membrane structure. It is well-known that myelin membranes are divided into subdomains with distinct protein and lipid composition. Nevertheless, it is unclear how these domains are generated and then maintained throughout the adult. Especially the mechanisms of interaction between cytoskeleton elements and membrane structures in the developing and adult myelin sheath are still unknown. In this work, the interaction of the cytoskeleton protein septin(Sept6) and the myelin and lymphocyte protein MAL is demonstrated. Septins are enriched in myelin membranes which is unique for cytoskeleton elements. Most important, the loss of Sept6 in myelin is compensated by its closest homolog Sept11 which clearly points to a functional role of septins in the myelin compartment. A detailed analysis of the septin protein family in myelinating cells was performed here. It was shown that septins are coordinately regulated during differentiation and myelination in Schwann cells and oligodendrocytes. On the protein level particular septins were identified to be differentially enriched in myelin membranes. They form distinct stoechiometric complexes interacting also with actin. We propose that septin/myelin membrane complexes play an important role in myelination. Septins might be crucial in the formation and maintenance of myelin subdomains as well as in the transport of myelin components. In line with this, a possible site of interaction between Sept6 and MAL was identified in the Schwann cell cytoplasm. There, Sept6 and MAL might be important for sorting and trafficking processes crucial for the targeting of myelin components into the emerging and adult myelin sheath. Sept6-deficient mice, however, did not disclose alterations in myelin ultrastructure and protein composition besides the upregulation of Sept11. But, it is well-known that the septin cortex is very robust and that homologous isoforms might compensate for the loss of single septins. In line with this, it is shown here that myelinating Schwann cells tolerate the loss of Sept2, which might be due to such compensation mechanisms. The function of Sept7 in myelination could not be elucidated, since downregulation in in vitro myelinating cultures led to unspecific effects probably on cytokinesis and cell survival. Nevertheless, this first comprehensive study on septins in oligodendrocytes and Schwann cells generated valuable data critical for further analysis of septin function in myelin. This study provides insight into the composition of the septin cytoskeleton, its regulation during myelination and its interaction with myelin membranes. Understanding the role of the septin cytoskeleton in myelin formation and maintenance may reveal new insights in the mechanisms of myelination and remyelination in health and disease
Immediate loading of implants with 3-unit fixed partial dentures: a 12-month clinical study
No full textPURPOSE: The aim of the present clinical trial was to evaluate the 12-month success rate of titanium dental implants placed in the posterior mandible and immediately loaded with 3-unit fixed partial dentures. MATERIALS AND METHODS: Patients with missing mandibular premolars and molars were enrolled in this study. To be included in the study, the implants had to show good primary stability. Implant stability was measured with resonance frequency analysis using the Osstell device (Integration Diagnostics). Implants were included in the study when the stability quotient (ISQ) exceeded 62. Clinical measurements, such as width of keratinized tissue, ISQ, and radiographic assessment of peri-implant bone crest levels, were performed at baseline and at the 12-month follow-up. The comparison between the baseline and the 12-month visits was performed with the Student t test for paired data (statistically significant at a level of alpha = 0.05). RESULTS: Forty implants with a sandblasted, large grit, acid-etched (SLA) surface (Straumann) were placed in 20 patients. At 12 months, only 1 implant had been lost because of an acute infection. The remaining 39 implants were successful, resulting in a 1-year success rate of 97.5%. Neither peri-implant bone levels, measured radiographically, nor implant stability changed significantly from baseline to the 12-month follow-up (P > .05). DISCUSSION: The immediate functional loading of implants placed in this case series study resulted in a satisfactory success rate. CONCLUSION: The findings from this clinical study showed that the placement of SLA transmucosal implants in the mandibular area and their immediate loading with 3-unit fixed partial dentures may be a safe and successful procedure
Diksi dalam Berita Kriminal Buser SCTV
No full textDalam kehidupannya, manusia tidak lepas dari kegiatan berbahasa. Dengan bahasa, manusia menyampaikan ide dan gagasannya kepada sesamanya. Terdapat perbendaharaan kata dalam sebuah bahasa sebagai alat komunikasi. Tapi, walaupun begitu, tidak serta merta seseorang menggunakan kata-kata tersebut secara sembarangan. Seseorang perlu memperhatikan masalah diksi agar tercipta komunikasi yang efektif dan tidak ada kesalahpahaman dalam sebuah proses komunikasi. Diksi adalah pemilihan kata yang tepat dalam suatu proses komunikasi untuk mempertegas maksud pembicara agar tidak terjadi kesalahpahaman antara pembicara dengan pendengar tentang ide dan gagasan yang disampaikan. Jika diksi yang dipakai tidak sesuai dengan konteks, maka akan terjadi kesalahpahaman tentang ide dan gagasan yang disampaikan. Masalah dalam penelitian ini adalah bagaimana penggunaan diksi dalam berita kriminal Buser SCTV, dari segi jenis diksi, strategi penggunaan diksi, dan perubahan makna diksi. Penelitian ini menggunakan pendekatan kualitatif dengan objek kajian siaran berita kriminal Buser yang ditayangkan di SCTV setiap hari pukul 11.30- 12.00. Pengumpulan data dilakukan dengan cara perekaman siaran Buser selama satu minggu. Metode yang dilakukan dalam penelitian ini adalah (1) transkripsi siaran Buser, (2) pengidentifikasian terhadap data, (3) pengklasifikasian terhadap kata yang termasuk kata umum dan khusus, kata kongkret dan abstrak, kata konotasi dan denotasi, kata standar dan nonstandar, penggunaan kata yang terkait dengan strategi, dan penggunaan kata yang mengalami perubahan makna, (4) pengkodean terhadap data-data yang diperoleh dan (5) penyimpulan terhadap penggunaan diksi dalam berita kriminal. Korpus data berupa satu kutipan yang meliputi kata-kata yang kehadirannya dianggap penting. Penelitian ini menghasilkan enam simpulan. Pertama, yang berhubungan dengan jenis diksi, yaitu (a) penggunaan kata umum dalam sebuah laporan berita sering digunakan pada bagian awal (lead) berita, sedangkan kata khusus digunakan pada bagian pengungkapan kronologis dari peristiwa kriminal yang dilaporkan, (b) penggunaan kata denotatif dalam laporan berita kriminal banyak digunakan untuk memberi informasi, sedangkan kata konotasi, walaupun bertentangan dengan hakikat berita sebagai media informasi, banyak ditemukan pemakaian kata konotatif sebagai alat untuk menunjukkan sikap sosial dari penulis berita (c) diksi abstrak dan kongkret digunakan dalam berita kriminal buser hanya sebatas sebagai pemberi informasi, (d) kata-kata nonstandar banyak digunakan dalam laporan berita kriminal Buser SCTV untuk membangun suasana yang komunikatif. Kedua, terdapat tiga strategi penggunaan diksi yang dipakai selain sebagai pemberi informasi, yaitu (a) mempersuasi seperti kata pelajaran iuntuk menjelaskan betapa bahayanya resiko semua pekerjaan, bahkan sebagai tukang ojek. Pekerjaan ini mengandung resiko, bahkan hingga bisa mengilangkan nyawa seseorang. Melalui pemakaian kata pelajaran, penutur bermaksud untuk mengingatkan kepada tukang ojek yang lain agar selalu waspada terhadap semua calon penumpangnya, (b) sikap sosial, contohnya dengan pemakaian kata konotasi tegar sengaja digunakan penutur berita untuk menunjukkan sebuah sikap sosial yang simpati terhadap nasib gadis cilik korban perkosaan, dan (c) Komunikatif, contohnya dengan pemakaian kata-kata nonstandar geger, maling, mengambang dan sebagainya. Ketiga, penggunaan diksi yang mengalami perubahan makna dalam laporan berita kriminal Buser SCTV meliputi perluasan makna, penyempitan makna, peninggian makna, penurunan makna, dan persamaan makna. Berdasarkan kesimpulan penelitian di atas, disarankan pada (1) peneliti lanjutan, untuk meneliti diksi dalam berita kriminal dengan jenis Depth news, Feature, atau jenis berita yang lain, (2) komentator dan pengulas bahasa, untuk memanfaatkan hasil penelitian ini agar dijadikan bahan referensi dalam penilaian terhadap laporan berita kriminal terutama dilihat dari segi diksinya, dan (3) penulis berita, untuk memanfaatkan hasil penelitian ini sebagai bahan masukan dalam penyusunan naskah berita agar lebih bisa mempertimbangkan efek yang ditimbulkan dari penggunaan diksi tertentu terhadap pendengar
Alchemilla subcrenata Buser inheems in Nederland
No full textUp to 1972 Alchemilla subcrenata Buser was regarded as doubtfully indigenous in the Netherlands. In this year, however, the occurrence of the species was recorded with certainty from the northern part of this country, viz. from a meadow along the brooklet Rolderdiep belonging to the area of glacial river beds Drentsche A. The most striking morphological characteristics of A. subcrenata are described, a number of details are given with regard to the habitat of the new locality and the distribution of this northern species is briefly discussed
Teaching Ichthyology Online with a Virtual Specimen Collection
No full textSidlauskas, Brian L., Burns, Michael D., Buser, Thaddaeus J., Harper, Nick, Kindred, Mark (2021): Teaching Ichthyology Online with a Virtual Specimen Collection. Ichthyology & Herpetology 109 (2): 407-423, DOI: 10.1643/t2020031, URL: https://www.mendeley.com/catalogue/edfc66b9-f42f-31e8-874e-ea89afa9df86
FIG. 10 in Teaching Ichthyology Online with a Virtual Specimen Collection
No full textFIG. 10. Annotated skull model of Artedius lateralis (OS6720) from CT scan data collected at the Karel F. Liem Imaging Facility at Friday Harbor, Washington. See the supplementary videos to view this model in motion (see Data Accessibility). (Credit: T. Buser and A. Summers).Published as part of Sidlauskas, Brian L., Burns, Michael D., Buser, Thaddaeus J., Harper, Nick & Kindred, Mark, 2021, Teaching Ichthyology Online with a Virtual Specimen Collection, pp. 407-423 in Ichthyology & Herpetology 109 (2) on page 420, DOI: 10.1643/t2020031, http://zenodo.org/record/784679
Immediate Restoration of Single-Tooth Implants in Mandibular Molar Sites: A 12-month Preliminary Report
No full textPURPOSE:
The aim of this prospective clinical study was to evaluate the survival rates at 12 months of transmucosal implants placed in the posterior mandible and immediately restored with single crowns.
MATERIALS AND METHODS:
Thirty ITI dental implants with sandblasted, acid-etched surfaces were placed in 30 patients missing at least 1 mandibular molar and immediately restored if acceptable primary stability was attained. Primary stability was measured with resonance frequency analysis (RFA) using the Osstell device, and only implants with a stability quotient greater than 62 were included in the study. RFA measurement and radiographic assessment were made at baseline and 6 months after implant placement. Plaque Index, Bleeding Index, probing depth, attachment level, and width of keratinized tissue were measured at the 12 month follow-up examination.
RESULTS:
At 12 months, only 1 implant had been lost; it was removed because of acute infection. Radiographic as well as clinical examination confirmed osseointegration of all implants, with a survival rate of 96.7%.
DISCUSSION:
Interestingly, implant stability as measured using RFA did not increase significantly from baseline to 12 months (P > .05).
CONCLUSION:
The present study showed that immediate restoration of transmucosal implants placed in the mandibular area with good primary stability can be a safe and successful procedure. However, larger, long-term clinical trials are needed to confirm the present results
Cultural activism and the politics of place-making
No full textIn this paper, we explore the relationship between creative practice, activism, and urban place-making by considering the role they play in the construction of meaning in urban spaces. Through an analysis of two activist groups based in Stokes Croft, Bristol (UK), we argue that cultural activism provides new political prospects within the wider context of global capitalism through the cultivation of a shared aesthetics of protest. By cultivating aspects of shared history and a mutual enthusiasm for creative practice as a form of resistance, Stokes Croft has emerged as a ‘space of nurturance’ for creative sensibilities. However, we note how Stokes Croft as an autonomous space remains open-ended and multiple for activists interested in promoting different visions of social justice
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