| 1. |
- Ackermann, M., et al.
(författare)
-
In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope
- 2012
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 35:6, s. 346-353
-
Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∌6 and ∌13 GeV with an estimated uncertainty of ∌2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.
|
|
| 2. |
- Ackermann, M., et al.
(författare)
-
Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data
- 2016
-
Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 819:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present results from gamma-ray observations of the Coma cluster incorporating six years of Fermi-LAT data and the newly released "Pass 8" event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the gamma-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100MeV are 1.7 x 10(-9) ph cm(-2) s(-1) and 5.2 x 10(-9) ph cm(-2) s(-1) respectively (the latter corresponds to residual emission at the level of 1.8 sigma). These bounds are comparable to or higher than predicted levels of hadronic gamma-ray emission in cosmic-ray (CR) models with or without reacceleration of secondary electrons, although direct comparisons are sensitive to assumptions regarding the origin and propagation mode of CRs and magnetic field properties. The minimal expected.-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.
|
|
| 3. |
- Tranberg, K. G., et al.
(författare)
-
Interstitial laser treatment of malignant tumours : Initial experience
- 1996
-
Ingår i: European Journal of Surgical Oncology. - 0748-7983. ; 22:1, s. 47-54
-
Tidskriftsartikel (refereegranskat)abstract
- This is a prospective pilot investigation of interstitial laser treatment. Twelve patients were treated at 13 sites: seven patients had metastatic or primary liver cancer (with a total of 21 tumour nodules), two had pancreatic carcinoma and four patients had disease at other sites. Treatments mere performed with an Nd-YAG laser, using a high power (6 or 10 W), short-time (5 min) technique or a feedback system for temperature regulation at low power (3 W) for 12-16 min. Treatment with high power invariably resulted in rapid carbonization of tissue, which may have contributed to the postoperative death in one patient. The local effect of treatment could be evaluated in 13 hepatic tumours (1.0-10 cm in diameter): 100% necrosis was seen in five and > 50% necrosis in the remaining eight. Two tumours were eradicated, five became smaller, and six remained unchanged in size or showed continued growth. Treatment removed or alleviated symptoms in 7/8 symptomatic patients. The feedback system made it possible to avoid carbonization and allowed better control of the tissue temperature. The main problem with either method was to monitor tissue changes in real time, and ultrasonography was found to be of little help in this respect. It is concluded that interstitial laser treatment is a promising method for treatment of tumours. Further development should focus on real-time monitoring and increased volume effect without carbonization.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Hannesson, P H, et al.
(författare)
-
Transhepatic intravascular ultrasound for evaluation of portal venous involvement in patients with cancer of the pancreatic head region.
- 2002
-
Ingår i: European Radiology. - : Springer Science and Business Media LLC. - 0938-7994 .- 1432-1084. ; 12:5, s. 1150-1154
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate the ability of intravascular ultrasound to diagnose tumor involvement of the portal and the superior mesenteric veins using the preoperative percutaneous, transhepatic approach, and to compare the findings with those made at concomitant direct portography, surgery, and histopathological examination. Ten patients with a preoperative diagnosis of a resectable tumor in the pancreatic head region were examined with percutaneous transhepatic portography (PTP) and intravascular ultrasound (IVUS). The surgeon's intraoperative evaluation and the histopathological examination in combination revealed tumor involvement of the portal or superior mesenteric veins in six of the ten patients. Percutaneous transhepatic portography suggested tumor involvement of the veins in six patients but two of the examinations were false positive and another two were false negative. Intravascular ultrasound showed signs of tumor involvement in eight patients. The examination was, however, false positive in two patients, but there were no false negatives. Complications of the percutaneous transhepatic procedure occurred in six patients including severe pain, bleeding, and related death. Percutaneous transhepatic IVUS of the portal vein may be a useful tool in the preoperative selection of the subgroup of patients with tumor of the pancreatic head region that could benefit from surgery. There is a need for technical improvement as well as studies with larger patient series to definitely decide the role of the technique.
|
|
