| 1. |
- Xu, Hao, et al.
(författare)
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Mechanisms of fluorescence decays of colloidal CdSe-CdS/ZnS quantum dots unraveled by time-resolved fluorescence measurement
- 2015
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 17:41, s. 27588-27595
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Tidskriftsartikel (refereegranskat)abstract
- By narrowing the detection bandpass and increasing the signal-to-noise ratio in measuring the time-resolved fluorescence decay spectrum of colloidal CdSe-CdS/ZnS quantum dots (QDs), we show that directly after the photoexcitation, the fluorescence decay spectrum is characterized by a single exponential decay, which represents the energy relaxation of the photogenerated exciton from its initial high-energy state to the ground exciton state. The fluorescence decay spectrum of long decay time is in the form of beta/t(2), where beta is the radiative recombination time of the ground-state exciton and t is the decay time. Our findings provide us with a direct and quantitative link between fluorescence decay measurement data and fundamental photophysics of QD exciton, thereby leading to a novel way of applying colloidal QDs to study microscopic, physical and chemical processes in many fields including biomedicine.
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| 2. |
- Bäck, Torbjörn, et al.
(författare)
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A TOF-PET system for educational purposes
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 477, s. 82-82
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Tidskriftsartikel (refereegranskat)abstract
- A TOF-PET system has been designed and constructed for educational purposes. The aim of this system is to demonstrate the possibilities of positron emission tomography in general and the time-of-flight method in particular to the students of various courses at the Royal Institute of Technology, Stockholm, Sweden. The set-up consists of 48 small BaF2 crystals coupled to fast photomultipliers placed in a ring geometry. The signals of the photomultipliers are fed into fast constant fraction discriminators (CFD). The outputs of these are directed to a specially designed logic VME unit. which combines the CFD signals of 6 neighbouring channels to one signal by adding a different delay to each channel. The logic circuitry produces a prompt pulse for each event that serves as the start pulse for the 8-channel fast TDC. The delayed pulses act as the stop pulses for the TDC. In a computer. the measured times are converted into information about which the photomultipliers fired with the difference in the time of flight. The set-up is described and the results are presented.
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| 3. |
- Kumar, Tharagan, et al.
(författare)
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Lab-in-a-fiber-based integrated particle separation and counting
- 2023
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Ingår i: Lab on a Chip. - : Royal Society of Chemistry. - 1473-0197 .- 1473-0189. ; 23, s. 2286-
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Tidskriftsartikel (refereegranskat)abstract
- An all-fiber integrated device capable of separating and counting particles is presented. A sequence of silica fiber capillaries with various diameters and longitudinal cavities are used to fabricate the component for size-based elasto-inertial passive separation of particles followed by detection in an uninterrupted continuous flow. Experimentally, fluorescent particles of 1 μm and 10 μm sizes are mixed in a visco-elastic fluid and fed into the all-fiber separation component. The particles are sheathed by an elasticity enhancer (PEO - polyethylene oxide) to the side walls. Larger 10 μm particles migrate to the center of the silica capillary due to the combined inertial lift force and elastic force, while the smaller 1 μm particles are unaffected, and exit from a side capillary. A separation efficiency of 100% for the 10 μm and 97% for the 1 μm particles is achieved at a total flow rate of 50 μL min−1. To the best of our knowledge, this is the first time effective inertial-based separation has been demonstrated in circular cross-section microchannels. In the following step, the separated 10 μm particles are routed through another all-fiber component for counting and a counting throughput of ∼1400 particles per min is demonstrated. We anticipate the ability to combine high throughput separation and precise 3D control of particle position for ease of counting will aid in the development of advanced microflow cytometers capable of particle separation and quantification for various biomedical applications.
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| 4. |
- Liamsuwan, Thiansin, 1984-, et al.
(författare)
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An energy-loss model for low- and intermediate-energy carbon projectiles in water
- 2012
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Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 88:1-2, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To model interaction cross sections and energy loss for carbon projectiles C(0)-C(6+) of 1-10(4) keV/u (u: atomic mass unit) in water. Materials and methods: The classical trajectory Monte Carlo method was used to calculate the ionisation and charge-transfer cross sections. The excitation cross sections were scaled from proton data using equilibrium charges determined from the charge-transfer cross sections. Energy loss was obtained from the singly differential cross sections, and ionisation potentials of the target and projectile. Results: The calculated total ionisation cross sections are consistent with measured data, while the calculated electron-capture cross sections are larger than experimental data by a factor of 3. By scaling the latter to the measured data, the cross sections were made consistent with these data for 1-10 keV/u energies. The present stopping cross sections agree well with experimental data below 10 keV/u, and with other model calculations above 2 MeV/u. Deviation from the latter is found where electron capture is competitive with ionisation, and also arises from different energy-transfer calculations. Conclusions: In this paper we report our efforts in the developments of full slowing-down Monte Carlo track structure calculations for carbon ions. Further development and refinement of the model are currently underway.
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| 5. |
- Löndahl, Jakob, et al.
(författare)
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Aerosol exposure versus aerosol cooling of climate: what is the optimal emission reduction strategy for human health?
- 2010
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324 .- 1680-7316. ; 10:19, s. 9441-9449
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Tidskriftsartikel (refereegranskat)abstract
- Particles, climate change, and health have thought-provoking interactions. Air pollution is one of the largest environmental problems concerning human health. On the other hand, aerosol particles can have a cooling effect on climate and a reduction of those emissions may result in an increased temperature globally, which in turn may have negative health effects. The objective of this work was to investigate the "total health effects" of aerosol emissions, which include both exposure to particles and consequences for climate change initiated by particles. As a case study the "total health effect" from ship emissions was derived by subtracting the number of deaths caused by exposure with the estimated number of lives saved from the cooling effect of the emissions. The analysis showed that, with current level of scientific understanding, it could not be determined whether ship emissions are negative or positive for human health on a short time scale. This first attempt to approximate the combined effect of particle emissions on health shows that reductions of particulate air pollution will in some cases (black carbon) have win-win effects on health and climate, but sometimes also cause a shift from particle exposure-related health effects towards an increasing risk of health consequences from climate change. Thus, measures to reduce aerosol emissions have to be coupled with climate change mitigation actions to achieve a full health benefit on a global level.
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| 6. |
- Minelli, Caterina, et al.
(författare)
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Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 14, s. 4690-4704
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Tidskriftsartikel (refereegranskat)abstract
- We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles.
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| 7. |
- Wiktorin, Anna H C, et al.
(författare)
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Mapping of Perfusion During Full-Thickness Blepharotomy Using Laser Speckle Contrast Imaging
- 2022
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Ingår i: Ophthalmic Plastic and Reconstructive Surgery. - 1537-2677. ; 38:6, s. 588-592
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was to monitor how the blood perfusion in human upper eyelids is affected during full-thickness blepharotomy.METHODS: Seven eyelids in 5 patients with upper eyelid retraction due to Graves' disease underwent full-thickness blepharotomy. Perfusion was measured using laser speckle contrast imaging in the eyelid margin and in the conjunctival pedicle.RESULTS: Immediately following the procedure, a nonsignificant reduction in perfusion was observed in the skin of the pretarsal eyelid margin, being 66% of the initial value (p = n.s.). However, a statistically significant decrease in perfusion, to 53% of the initial value (p < 0.01), was seen in the central pedicle of the conjunctiva. There were no surgical complications such as infection, signs of ischemia, or bleeding.CONCLUSIONS: In this study, eyelid perfusion was mapped during full-thickness blepharotomy for the first time using laser speckle contrast imaging. The results showed that perfusion is sufficiently preserved during surgery, probably due to the rich vascular supply in the periocular region, which may explain the low risk of postoperative complications such as ischemia and infection.
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