| 1. |
- Crenshaw, D. M., et al.
(author)
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Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
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Journal article (peer-reviewed)abstract
- Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines
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| 2. |
- Edelson, R. A., et al.
(author)
-
Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
- 1996
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
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Journal article (peer-reviewed)abstract
- For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)
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| 3. |
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| 4. |
- Miller, T. C., et al.
(author)
-
Particle astrophysics in antarctica
- 1996
-
In: International School of Cosmic Ray Astrophysics: 10th Course: Toward the Millennium in Astrophysics: Problems and Prospects 16-26 Jun 1996. Erice, Italy. ; , s. 157-166
-
Conference paper (peer-reviewed)
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| 5. |
- Askebjer, P., et al.
(author)
-
Optical properties of deep ice at the South Pole : Absorption
- 1997
-
In: Applied Optics. - : Optical Society of America. - 0003-6935 .- 1539-4522. ; 36:18, s. 4168-4180
-
Journal article (peer-reviewed)abstract
- We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ∼415 to ∼500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.
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| 6. |
- Askebjer, P., et al.
(author)
-
UV and optical light transmission properties in deep ice at the South Pole
- 1997
-
In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 24:11, s. 1355-1358
-
Journal article (peer-reviewed)abstract
- Both absorption and scattering of light at wavelengths 410 to 610 nanometers were measured in the South Pole ice at depths 0.8 to 1 kilometer with the laser calibration system of the Antarctic Muon And Neutrino Detector Array (AMANDA). At the shortest wavelengths the absorption lengths exceeded 200 meters - an order of magnitude longer than has been reported for laboratory ice. The absorption shows a strong wavelength dependence while the scattering length is found to be independent of the wavelength, consistent with the hypothesis of a residual density of air bubbles in the ice. The observed linear decrease of the inverse scattering length with depth is compatible with an earlier measurement by the AMANDA collaboration (at ∼515 nanometers).
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| 7. |
- Bergstrom, L., et al.
(author)
-
The AMANDA experiment : Status and prospects for indirect dark matter detection
- 1996
-
In: The identification of dark matter. Proceedings, 1st International Workshop, Sheffield, UK, September 8-12, 1996. ; , s. 521-528
-
Conference paper (peer-reviewed)abstract
- At the AMANDA South Pole site, four new holes were drilled to depths 2050m to 2180 m and instrumented with 86 photomultipliers (PMTs) at depths1520-2000 m. Of these PMTs 79 are working, with 4-ns timing resolutionand noise rates 300 to 600 Hz. Various diagnostic devices were deployedand are working. An observed factor 60 increase in scattering length anda sharpening of the distribution of arrival times of laser pulses relative tomeasurements at 800-1000 m showed that bubbles are absent below 1500 m.Absorption lengths are 100 to 150 m at wavelengths in the blue and UV to337 nm. Muon coincidences are seen between the SPASE air shower arrayand the AMANDA PMTs at 800-1000 m and 1500-1900 m. The muon trackrate is 30 Hz for 8-fold triggers and 10 Hz for 10-fold triggers. The presentarray is the nucleus for a future expanded array. The potential of AMANDAfor SUSY dark matter search through the detection of high-energy neutrinosfrom the centre of the Sun or Earth is discussed.
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| 8. |
- Hulth, P. O., et al.
(author)
-
The AMANDA experiment
- 1996
-
In: Neutrino '96. Proceedings, 17th International Conference on Neutrino Physics and Astrophysics, Helsinki, Finland, June 13-19, 1996. ; , s. 518-523
-
Conference paper (peer-reviewed)abstract
- At the AMANDA South Pole site, four new holes were drilled to depths 2050 m to 2180 m and instrumented with 86 photomultipliers (PMTs) at depths 1520-2000 m. Of these PMTs 79 are working, with 4-ns timing resolution and noise rates 300 to 600 Hz. Various diagnostic devices were deployed and are working. An observed factor 60 increase in scattering length and a sharpening of the distribution of arrival times of laser pulses relative to measurements at 800-1000 m showed that bubbles are absent below 1500 m. Absorption lengths are 100 to 150 m at wavelengths in the blue and UV to 337 nm. Muon coincidences are seen between the SPASE air shower array and the AMANDA PMTs at 800-1000 m and 1500-1900 m. The muon track rate is 30 Hz for 8-fold triggers and 10 Hz for 10-fold triggers. The present array is the nucleus for a future expanded array.
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| 9. |
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| 10. |
- Askebjer, P., et al.
(author)
-
AMANDA : status report from the 1993-94 campaign and optical properties of the South Pole ice
- 1995
-
In: Nuclear physics B, Proceedings supplements. - : Elsevier. - 0920-5632 .- 1873-3832. ; 38:1-3, s. 287-292
-
Journal article (peer-reviewed)abstract
- We report the first results of the AMANDA detector. During the antarctic summer 1993-94 four strings were deployed between 0.8 an 1 km depth, each equipped with 20 photomultiplier tubes (PMTs). A laser source was used to investigate the optical properties of the ice in situ. We find that the ice is intrinsically extremely transparent. The measured absorption length is 59 ± 3 m, i.e. comparable with the quality of the ultra-pure water used in the IMB and Kamiokande proton-decay and neutrino experiments [1,2] and more than two times longer than the best value reported for laboratory ice [3]. Due to a residual density of air bubbles at these depths, the motion of photons in the medium is randomized. For spherical, smooth bubbles we find that, at 1 km depth, the average distance between collisions is about 25 cm. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated. © 1995 Elsevier Science B.V. All rights reserved.
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| 11. |
- Askebjer, P., et al.
(author)
-
On the age vs depth and optical clarity of deep ice at South Pole
- 1995
-
In: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 41:139, s. 445-454
-
Journal article (peer-reviewed)abstract
- The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the South Pole. During the 1995-96 season an additional six strings will be deployed at greater depths. Provided absorption, scattering, and refraction of visible light are sufficiently small, the trajectory of a muon into which a neutrino converts can be determined by using the array of phototubes to measure the arrival times of \v{C}erenkov light emitted by the muon. To help in deciding on the depth for implantation of the six new strings, we discuss models of age vs depth for South Pole ice, we estimate mean free paths for scattering from bubbles and dust as a function of depth, and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hydrate inclusions and normal ice. We conclude that the depth interval 1600 to 1800 m will be suitably transparent for the next six AMANDA strings and, moreover, that the interval 1600 to 2100 m will be suitably transparent for a future 1-km 3 observatory except possibly in a region a few tens of meters thick at a depth corresponding to a peak in the dust concentration at 60 kyr BP.
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| 12. |
- Askebjer, P., et al.
(author)
-
Optical properties of the South Pole ice at depths between 0.8 and 1 kilometer
- 1995
-
In: Science. - 0036-8075 .- 1095-9203. ; 267:5201, s. 1147-1150
-
Journal article (peer-reviewed)abstract
- The optical properties of the ice at the geographical South Pole have been investigated at depths between 0.8 and 1 kilometer. The absorption and scattering lengths of visible light (∼515 nanometers) have been measured in situ with the use of the laser calibration setup of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino detector. The ice is intrinsically extremely transparent. The measured absorption length is 59 ± 3 meters, comparable with the quality of the ultrapure water used in the Irvine-Michigan-Brookhaven and Kamiokande proton-decay and neutrino experiments and more than twice as long as the best value reported for laboratory ice. Because of a residual density of air bubbles at these depths, the trajectories of photons in the medium are randomized. If the bubbles are assumed to be smooth and spherical, the average distance between collisions at a depth of 1 kilometer is about 25 centimeters. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated.
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| 13. |
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| 14. |
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| 15. |
- Mock, P. C., et al.
(author)
-
Status and capabilities of AMANDA-94
- 1995
-
In: Proceedings, 24th International Conference, Rome, Italy, August 28-September 8, 1995.
-
Conference paper (peer-reviewed)
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| 16. |
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| 17. |
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| 18. |
- Kim, S.K., et al.
(author)
-
Binding Geometries of Triple Helix Selective Benzopyrido [4,3-b]indole Ligands Complexed with Double- and Triple-Helical Polynucleotides
- 1997
-
In: Biopolymers. - 0006-3525 .- 1097-0282. ; 42:1, s. 101-111
-
Journal article (peer-reviewed)abstract
- The binding modes of three benzopyrido[4,3-b]indole derivatives (and one benzo[f]pyrido[4-3b]quinoxaline derivative) with respect to double helical poly(dA) . poly(dT) and poly[d(A-T)](2) and triple-helical poly(dA) . 2poly(dT) have been investigated using linear dichroism (LD) and CD: (I) 3-methoxy-11-amino-BePI where BePI = {7H-8-methyl-benzo[e]pyrido[4,3-b]indole}, (II) 3-methoxy-11-[(3'-amino)propylamino]-BePI, (III) 3-methoxy-7-[(3'diethylamino)propylamino]BgPI where BgPI = {benzo[g]pyrido[4,3-b]indole}, and (IV) 3-methoxy-11-[(3'amino)propylamino]BfPQ where BfPQ = {benzo[f]pyrido[4-3b]quinoxaline}. The magnitudes of the reduced LD of the electronic transitions of the polynucleotide bases and of the bound ligands are generally very similar, suggesting an orientation of the plane of the ligands' fused-ring systems preferentially perpendicular to the helix axis. The LD results suggest that all of the ligands are intercalated for all three polynucleotides. The induced CD spectrum of the BePI chromophore in the (II-BePI)-poly[d(A-T)](2) complex is almost a mirror image of that for the (I-BePI)-poly(dA) . poly(dT) and (I-BePI)-poly(dA) . 2poly(dT) complexes, suggesting an antisymmetric orientation of the BePI moiety upon intercalation in poly[d(A-T)]2 compared to the other polynucleotides. The induced CD of I-BePI bound to poly(dA) . 2poly(dT) suggests a geometry that is intermediate between that of its other two complexes. The concluded intercalative binding as well as the conformational variations between the different BePI complexes are of interest in relation to the fact that BePI derivatives are triplex stabilizers.
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| 19. |
- Sun, H., et al.
(author)
-
New Band Structures and an Unpaired Crossing in 78Kr
- 1999
-
In: Physical Review C (Nuclear Physics). - 0556-2813. ; 59:2, s. 655-664
-
Journal article (peer-reviewed)abstract
- High-spin states in Kr-78 were studied using the Ni-58(Na-23,3p) reaction at 70 MeV and the Ni-58(Si-23,alpha 4p) reaction at 130 MeV. Prompt gamma-gamma coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24(+) state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. [S0556-2813(99)04602-6].
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| 20. |
- Hammarstrom, L, et al.
(author)
-
Mimicking photosystem II reactions in artificial photosynthesis
- 1999
-
In: ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS. - : R OLDENBOURG VERLAG. - 0942-9352. ; 213, s. 157-163
-
Journal article (peer-reviewed)abstract
- The paper describes a project aiming at the construction of functional mimics of the oxygen evolving complex of Photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors - manganese complexes and tyrosine - have been linked to
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| 21. |
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| 22. |
- Sun, X F, et al.
(author)
-
A novel p53 germline alteration identified in a late onset breast cancer kindred
- 1996
-
In: Oncogene. - 0950-9232. ; 13:2, s. 11-407
-
Journal article (peer-reviewed)abstract
- Germline mutations in the p53 tumor suppressor gene are associated with the Li-Fraumeni syndrome, characterized by childhood sarcoma, leukemia and early onset breast cancer and has occasionally been found also in familial breast-ovarian cancer. Most mutations found are of missense type and located in the central region of the gene (exons 5 to 8). In the present study, a germline p53 alteration was identified in a late onset breast cancer family (kindred Lund 5; mean age 58 years) using single stranded conformation polymorphism and sequence analysis. The mutation (a CCG to CTG transition) at codon 82 in exon 4, resulting in a proline to leucine substitution, has not previously been reported and was not present in a control set of 60 healthy individuals. Three of five woman with breast cancer (45, 57 and 65 years) were carriers of the alteration. Loss of heterozygosity at the p53 locus was not seen in the primary tumors of these women, but appeared as a partial loss of the wildtype allele in subsequent recurrent lesions of two gene carriers. The family manifested no linkage to the p53 gene (a two-point LOD-score of -0.41), and has previously also been excluded for linkage to the BRCA1 and BRCA2 loci, as well as being carrier of a BRCA1 germline mutation. Although it seems unlikely that the p53 germline mutation is the major cause of disease predisposition in Lund 5, the data suggest that some p53 alteration may confer a subtle influence on breast cancer development and progression.
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| 23. |
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| 24. |
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