| 11. |
- Axelsson, Magnus, et al.
(author)
-
Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite
- 2007
-
In: Astroparticle Physics. - : Elsevier BV. - 0927-6505. ; 28:3, s. 327-337
-
Journal article (peer-reviewed)abstract
- Linear polarization in X- and γ-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper, we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25–100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 h were simulated, corresponding to a standard and a long duration flight, respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.
|
|
| 12. |
- Kiss, Mózsi, et al.
(author)
-
The PoGOLite balloon-borne soft gamma-ray polarimeter
- 2008
-
In: COOL DISCS, HOT FLOWS. - : AIP. ; , s. 225-232
-
Conference paper (peer-reviewed)abstract
- Linearly polarized radiation in the hard X-ray/soft gamma-ray band is expected from a large variety of astronomical sources. We discuss the importance of polarimetric studies for several classes of sources - pulsars, accreting black holes. magnetic neutron stars and jets from active galaxies - and then describe PoGOLite, a balloon-borne instrument which is currently under construction and will be able to measure the polarization of electromagnetic radiation from such extra-solar objects in the energy range 25-80 keV.
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
- Klionsky, Daniel J., et al.
(author)
-
Guidelines for the use and interpretation of assays for monitoring autophagy in higher eukaryotes
- 2008
-
In: Autophagy. - : Landes Bioscience. - 1554-8627 .- 1554-8635. ; 4:2, s. 151-175
-
Research review (peer-reviewed)abstract
- Research in autophagy continues to accelerate,1 and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.2,3 There are many useful and convenient methods that can be used to monitor macroautophagy in yeast, but relatively few in other model systems, and there is much confusion regarding acceptable methods to measure macroautophagy in higher eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers of autophagosomes versus those that measure flux through the autophagy pathway; thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from fully functional autophagy that includes delivery to, and degradation within, lysosomes (in most higher eukaryotes) or the vacuole (in plants and fungi). Here, we present a set of guidelines for the selection and interpretation of the methods that can be used by investigators who are attempting to examine macroautophagy and related processes, as well as by reviewers who need to provide realistic and reasonable critiques of papers that investigate these processes. This set of guidelines is not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to verify an autophagic response.
|
|
| 16. |
|
|
| 17. |
- Kamae, Tuneyoshi, et al.
(author)
-
PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter
- 2008
-
In: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 30:2, s. 72-84
-
Journal article (peer-reviewed)abstract
- We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.
|
|
| 18. |
- Lu, Mai, 1968, et al.
(author)
-
Calculating the activating function in the human brain by transcranial magnetic stimulation
- 2007
-
In: IEEE Transactions on Magnetics. - 0018-9464. ; 44:6, s. 1438-1441
-
Conference paper (peer-reviewed)abstract
- It has been shown that the negative gradient of the component of the electric field, called the activating function, contributes to nerve excitation. In this paper, the induced electric field in a 3-D human head model by transcranial magnetic stimulation (TMS) has been calculated by employing the impedance method. The activating functions are then obtained by gradient operations to the three components of the induced electric field. The activating functions are scattered over the different brain tissues. Peaks of the activating functions are presented at the interfaces of the different tissues. The largest values of the activating functions are presented in the cerebral spinal fluid. (CSF). Results in this paper will be beneficial to the TMS applications in clinic as well as in the brain research.
|
|
| 19. |
- Lu, M., et al.
(author)
-
Calculating the Current Density and Electric Field in Human Head by Multichannel Transcranial Magnetic Stimulation
- 2009
-
In: IEEE Transactions on Magnetics. - 0018-9464. ; 45:3, s. 1662-1665
-
Journal article (peer-reviewed)abstract
- In this paper, we present a designed multichannel transcranial magnetic stimulation (mTMS) system with 40 small coils. The induced current density and electric field in realistic human head model by mTMS were calculated by impedance method and the results were compared with figure-of-eight coil. The dependence of stimulation focality on the coil current direction was investigated. Properly adjusting the input current phases can improve the magnitude of the induced fields in the brain.
|
|
| 20. |
|
|
