| 1. |
- Ansell, Ricky, et al.
(författare)
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Contamination monitoring in the forensic DNA laboratory and a simple graphical model for unbiased EPG classification
- 2011
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Ingår i: Book of Abstracts. ; , s. 199-
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Konferensbidrag (refereegranskat)abstract
- In this work we present a procedure for contamination monitoring in a trace search and recovery area and agraphical classification model. The recent launch of more sensitive and robust amplification kits increases thepossibility to detect minute amounts of trace DNA. As a consequence this enhances our need to establish eliminationdatabases and demands for an increased awareness on how to avoid contamination. DNA contaminatingthe evidence somewhere along the forensic process has the potential to destroy the evidence or totally confuseand mislead the crime investigation. In the forensic laboratory specific areas are designated for different partsof the process: trace search and recovery, pre-PCR, post-PCR etc. Work procedures and cleaning routines areadapted to minimise the risk of contamination. Monitoring presence of DNA in the laboratory environment, onspecific surfaces or instruments of interest, is one way to assess these risks and will in addition increase ourknowledge on how to improve cleaning routines and behaviour in the lab. A monitoring process needs to someextent be standardised in order to become unbiased and independent on an individual level, regarding bothwhere and how samples are taken and how the results are classified. The graphical model constitutes a lineartransformation of a three-dimensional “credit system” based on alleles, markers and peak heights, into a twodimensional classification. The standardisation allows results to be compared over time, and if applied to otherwork-areas comparison between different parts of the process will be possible.
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| 2. |
- Chaitanya, Lakshmi, et al.
(författare)
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Collaborative EDNAP exercise on the IrisPlex system for DNA based prediction of human eye colour
- 2014
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Ingår i: Forensic Science International. - : Elsevier. - 1872-4973 .- 1878-0326. ; 11, s. 241-251
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Tidskriftsartikel (refereegranskat)abstract
- The IrisPlex system is a DNA-based test system for the prediction of human eye colour from biological samples and consists of a single forensically validated multiplex genotyping assay together with a statistical prediction model that is based on genotypes and phenotypes from thousands of individuals. IrisPlex predicts blue and brown human eye colour with, on average, >94% precision accuracy using six of the currently most eye colour informative single nucleotide polymorphisms (HERC2 rs12913832, OCA2 rs1800407, SLC24A4 rs12896399, SLC45A2 (MATP) rs16891982, TYR rs1393350, and IRF4 rs12203592) according to a previous study, while the accuracy in predicting non-blue and non-brown eye colours is considerably lower. In an effort to vigorously assess the IrisPlex system at the international level, testing was performed by 21 laboratories in the context of a collaborative exercise divided into three tasks and organised by the European DNA Profiling (EDNAP) Group of the International Society of Forensic Genetics (ISFG). Task 1 involved the assessment of 10 blood and saliva samples provided on FTA cards by the organising laboratory together with eye colour phenotypes; 99.4% of the genotypes were correctly reported and 99% of the eye colour phenotypes were correctly predicted. Task 2 involved the assessment of 5 DNA samples extracted by the host laboratory from simulated casework samples, artificially degraded, and provided to the participants in varying DNA concentrations. For this task, 98.7% of the genotypes were correctly determined and 96.2% of eye colour phenotypes were correctly inferred. For Tasks 1 and 2 together, 99.2% (1875) of the 1890 genotypes were correctly generated and of the 15 (0.8%) incorrect genotype calls, only 2 (0.1%) resulted in incorrect eye colour phenotypes. The voluntary Task 3 involved participants choosing their own test subjects for IrisPlex genotyping and eye colour phenotype inference, while eye photographs were provided to the organising laboratory and judged; 96% of the eye colour phenotypes were inferred correctly across 100 samples and 19 laboratories. The high success rates in genotyping and eye colour phenotyping clearly demonstrate the reproducibility and the robustness of the IrisPlex assay as well as the accuracy of the IrisPlex model to predict blue and brown eye colour from DNA. Additionally, this study demonstrates the ease with which the IrisPlex system is implementable and applicable across forensic laboratories around the world with varying pre-existing experiences.
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| 3. |
- Nilsson, Ricky, 1979-
(författare)
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Circumstellar Debris Disks : Observational Studies of Cold Dust and Gas Emission in Planetary Nurseries
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Planetary systems form in disks of gas and dust surrounding newborn stars. The young circumstellar environment is characterized by frequent collisions between rocky bodies, leading to a continuous production of small dust grains. Such collisional processing persists in leftover debris disks or belts akin to the Solar System's asteroid and Kuiper belts, during the star's entire main-sequence lifetime. This thesis presents observations of thermal emission from cold dust in extended debris disks, in addition to spatially resolved observations of dust scattered light and gas emission in nearby debris disk systems. A total of 30 debris disk candidates identified from infrared excess were observed at submillimeter (submm) wavelengths with the Atacama Pathfinder EXperiment (APEX) telescope in search for dust at radial distances corresponding to the Kuiper belt or beyond. Two observing campaigns with the PolCor instrument at the Nordic Optical Telescope (NOT), performing optical polarimetric coronagraphy to resolve scattered light from nearby disks were also carried out. The edge-on debris disk surrounding the star β Pictoris was explored using integral-field spectroscopy with the Very Large Telescope (VLT) in an attempt to map the spatial distribution of previously detected gas. The APEX observations detected 14 exo-Kuiper belts, out of which 7 were new discoveries in the submm region. Modeling of the spectral energy distribution from available photometry and detected submm fluxes allowed us to study the dependence of the fractional dust luminosity and characteristic radial dust distance on stellar spectral type and age. The results indicate a decrease in fractional dust luminosity as t-α, where t is the age of the system and α = 0.8–2.0. From the VLT data we retrieved the first complete image of Ca II and Fe I emission in the disk of β Pictoris. Subsequent modeling demonstrated that the anomalous vertical structure of the observed Ca II emission can be explained by an optically thick disk midplane.
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| 4. |
- Nilsson, Ricky, 1979-, et al.
(författare)
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Kuiper belts around nearby stars
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. A40-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The existence of dusty debris disks around a large fraction of solar type main-sequence stars, inferred from excess far-IR and submillimetre emission compared to that expected from stellar photospheres, suggests that leftover planetesimal belts analogous to the asteroid-and comet reservoirs of the solar system are common. Aims. Sensitive submillimetre observations are essential to detect and characterise cold extended dust originating from collisions of small bodies in disks, belts, or rings at Kuiper-belt distances (30-50 AU or beyond). Measurements of the flux densities at these wavelengths will extend existing IR photometry and permit more detailed modelling of the Rayleigh-Jeans tail of the disks spectral energy distribution (SED), effectively constraining dust properties and disk extensions. By observing stars spanning from a few up to several hundred Myr, the evolution of debris disks during crucial phases of planet formation can be studied. Methods. We observed 22 exo-Kuiper-belt candidates at 870 mu m, as part of a large programme with the LABOCA bolometer at the APEX telescope. Dust masses (or upper limits) were calculated from integrated 870 mu m fluxes, and fits to the SED of detected sources revealed the fractional dust luminosities f(dust), dust temperatures T(dust), and power-law exponents beta of the opacity law. Results. A total of 10 detections with at least 3 sigma significance were made, out of which five (HD95086, HD131835, HD161868, HD170773, and HD207129) have previously never been detected at submillimetre wavelengths. Three additional sources are marginally detected with > 2.5 sigma significance. The best-fit beta parameters all lie between 0.1 and 0.8, in agreement with previous results indicating the presence of significantly larger grains than those in the ISM. From our relatively small sample we estimate f(dust) proportional to t(-alpha), with a similar to 0.8-2.0, and identify an evolution of the characteristic radial dust distance R(dust) that is consistent with the t(1/3) increase predicted from models of self-stirred collisions in debris disks.
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