| 1. |
- Acciari, V. A., et al.
(författare)
-
Radio Imaging of the Very-High-Energy gamma-Ray Emission Region in the Central Engine of a Radio Galaxy
- 2009
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5939, s. 444-448
-
Tidskriftsartikel (refereegranskat)abstract
- The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
|
|
| 2. |
- Häggblad, Robert, et al.
(författare)
-
Substituted Mo-V(Ti)-Te(Ce)-oxide M2 catalysts for propene ammoxidation
- 2008
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 50:1-4, s. 52-65
-
Tidskriftsartikel (refereegranskat)abstract
- One of the most effective propane to acrylonitrile ammoxidation catalyst is comprised of the two phases M1 (orthorhombic) Mo7.5V1.5NbTeO29 and M2 (pseudo-hexagonal) Mo4V2Te2O20. Under reaction conditions, the two phases work in symbiosis with each other where M1 is the paraffin activating component and M2 is the olefin activating component. Since the catalytic improvement of either phase should result in an enhancement of the overall acrylonitrile yield, controlled substitution of certain elements in either or both phases might result in the desired improvement. Our current study concentrates on the partial substitutions of V with Ti and Te with Ce in the M2 phase. Ti substitution results in a considerable propene activity improvement, whereas the selectivity to acrylonitrile is unaffected. Substitution with Ce, on the contrary, substantially improves the selectivity to acrylonitrile. Also, a minor improvement of the activity is notable. The acrylonitrile selectivity improvement is a result of better NH3 utilization and comes at the expense of reduced acrolein make. XRD reveals that all of the substituted compositions retain the M2 structure and essentially are monophasic. XANES recordings show for the bulk that the Mo is 6+, the V is 4+, or 4+ and 5+ when Ce is present, the Ti is 4+, the Ce is 3+, and the Te 4+ with some 6+ also present. According to the ESR data, in the M2 with Ce (7Te/3Ce) only 21% of the V is 4+, the remainder being 5+, which tentatively can be explained by the existence of some cation vacancies in the hexagonal channels. HRTEM imaging reveals little if any differences between the materials, all have the typical pseudo-hexagonal habit of the M2 phase and expose a 1-2 nm thick surface layer without any apparent long-range ordering. XPS data show that all catalysts, including the base, are highly enriched at the surface with Te at the expense of other metals. The 7Te/3Ce composition exhibits also substantial Ce surface enrichment. Moreover, the valences of the cations at the surface differ from the bulk in that for all fresh catalysts V is 5+ and Te is 6+ on the surface. Characterization by XPS of catalysts used in propene ammoxidation, reveals reduction of Te and, except when Ce is present, also Mo. Therefore, it might be inferred that the surfaces of the catalysts studied here are comprised essentially of one or a few monolayers of TeMoO or TeCeMoO on an interacting M2 crystalline base.
|
|
| 3. |
|
|
| 4. |
- Strauss, David G, et al.
(författare)
-
ECG Quantification of Myocardial Scar in Cardiomyopathy Patients With or Without Conduction Defects Correlation With Cardiac Magnetic Resonance and Arrhythmogenesis
- 2008
-
Ingår i: Circulation: Arrhythmia and Electrophysiology. - 1941-3084. ; 1:5, s. 327-336
-
Tidskriftsartikel (refereegranskat)abstract
- Background-Myocardial scarring from infarction or nonischemic fibrosis forms arrhythmogenic substrate. The Selvester QRS score has been extensively validated for estimating myocardial infarction scar size in the absence of ECG confounders. but has not been tested to quantify scar in patients with hypertrophy, bundle branch/fascicular blocks, or nonischemic cardiomyopathy. We assessed the hypotheses that (1) QRS scores (modified for each ECG coil founder) correctly identify and quantify scar in ischemic and nonischemic patients when compared with the reference standard of cardiac magnetic resonance using, late-gadolinium enhancement, and (2) QRS-estimated scar size predicts inducible sustained monomorphic ventricular tachycardia during electrophysiological testing. Methods and Results-One hundred sixty-two patients with left ventricular ejection fraction <= 35% (95 ischemic, 67 nonischemic) received 12-lead ECG and cardiac magnetic resonance using late-gadolinium enhancement before implantable cardioverter defibrillator placement for primary prevention of sudden cardiac death. QRS scores correctly diagnosed cardiovascular magnetic resonance scar presence with receiver operating characteristics area under the curve of 0.91 and correlation for scar quantification of r=0.74 (P<0.0001) for all patients. Performance within hypertrophy. conduction defect. and nonischemic sub-groups ranged from area Under the curve of 0.81 to 0.94 and r=0.60 to 0.80 (P<0.001 for all). Among the 137 patients undergoing electrophysiological or device testing, each 3-point QRS-score increase (9% left ventricular scarring) was associated with an odds ratio for inducing monomorphic ventricular tachycardia of 2.2 (95% CI 1.5 to 3.2; P<0.001) for all patients, 1.7 (1.0 to 2.7. P=0.04) for ischemics, and 2.2 ( 1.0 to 5.0, P=0.05) for nonischemics. Conclusions-QRS scores identify and quantify scar in ischemic and nonischemic cardiomyopathy patients despite ECG confounders. Higher QRS-estimated scar size is associated with increased arrhythmogenesis and warrants further study as a risk-stratifying tool. (Circ Arrhythmia Electrophysiol. 2008;1:327-336.)
|
|
