| 1. |
- Michael, Eli, et al.
(författare)
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Hubble Space Telescope Observations of High-Velocity Lyα and Hα Emission from Supernova Remnant 1987A : The Structure and Development of the Reverse Shock
- 2003
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 593, s. 809-830
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Tidskriftsartikel (refereegranskat)abstract
- We present two-dimensional line profiles of high-velocity (~+/-12,000 km s-1) Lyα and Hα emission from supernova remnant 1987A obtained with the Space Telescope Imaging Spectrograph between 1997 September and 2001 September (days 3869-5327 after the explosion). This emission comes from hydrogen in the debris that is excited and ionized as it passes through the remnant's reverse shock. We use these profiles to measure the geometry and development of the reverse-shock surface. The observed emission is confined within ~+/-30° about the remnant's equatorial plane. At the equator, the reverse shock has a radius of ~75% of the distance to the equatorial ring. We detect marginal differences (6%+/-3%) between the location of the reverse-shock front in the northeast and southwest parts of the remnant. The radius of the reverse shock surface increases for latitudes above the equator, a geometry consistent with a model in which the supernova debris expands into a bipolar nebula. Assuming that the outer supernova debris has a power-law density distribution, we can infer from the reverse-shock emission light curve an expansion rate (in the northeast part of the remnant) of 3700+/-900kms-1, consistent with the expansion velocities determined from observations in radio (Manchester et al.) and X-ray (Park et al.; Michael et al.) wavelengths. However, our most recent observation (at day 5327) suggests that the rate of increase of mass flux across the northeast sector of the reverse shock has accelerated, perhaps because of deceleration of the reverse shock caused by the arrival of a reflected shock created when the blast wave struck the inner ring. Resonant scattering within the supernova debris causes Lyα photons created at the reverse shock to be directed preferentially outward, resulting in a factor of ~5 difference in the observed brightness of the reverse shock in Lyα between the near and far sides of the remnant. Accounting for this effect, we compare the observed reverse-shock Lyα and Hα fluxes to infer the amount of interstellar extinction by dust as E(B-V)=0.17+/-0.01 mag. We also notice extinction by dust in the equatorial ring with E(B-V)~0.02-0.08 mag, which implies dust-to-gas ratios similar to that of the LMC. Since Hα photons are optically thin to scattering, the observed asymmetry in brightness of Hα from the near and far sides of the remnant represents a real asymmetry in the mass flux through the reverse shock of ~30%. We discuss future observational strategies that will permit us to further investigate the reverse-shock dynamics and resonant scattering of the Lyα line and to constrain better the extinction by dust within and in front of the remnant.
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| 2. |
- Li, Xiaofeng, et al.
(författare)
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Fibroblast growth factor signaling and basement membrane assembly are connected during epithelial morphogenesis of the embryoid body
- 2001
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Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 153:4, s. 811-822
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Tidskriftsartikel (refereegranskat)abstract
- Fibroblast growth factors and receptors are intimately connected to the extracellular matrix by their affinity to heparan sulfate proteoglycans. They mediate multiple processes during embryonic development and adult life. In this study, embryonic stem cell-derived embryoid bodies were used to model fibroblast growth factor signaling during early epithelial morphogenesis. To avoid redundancy caused by multiple receptors, we employed a dominant negative mutation of Fgfr2. Mutant-derived embryoid bodies failed to form endoderm, ectoderm, and basement membrane and did not cavitate. However, in mixed cultures they displayed complete differentiation induced by extracellular products of the normal cell. Evidence will be presented here that at least one of these products is the basement membrane or factors connected to it. It will be shown that in the mutant, collagen IV and laminin-1 synthesis is coordinately suppressed. We will demonstrate that the basement membrane is required for embryoid body differentiation by rescuing columnar ectoderm differentiation and cavitation in the mutant by externally added basement membrane proteins. This treatment induced transcription of Eomesodermin, an early developmental gene, suggesting that purified basement membrane proteins can activate inherent developmental programs. Our results provide a new paradigm for the role of fibroblast growth factor signaling in basement membrane formation and epithelial differentiation.
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| 3. |
- Andrekson, Peter, 1960, et al.
(författare)
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Nonlinearity-based all-optical sampling of ultrahigh-bandwidth optical signals
- 2004
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5596, s. 319-331
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Konferensbidrag (refereegranskat)abstract
- We demonstrate an all-optical waveform sampling system with simultaneous sub-mW optical signal sensitivity (20 dB SNR) and sub-picosecond temporal resolution over more than 60 nm optical bandwidth. The optical sampling was implemented by four-wave mixing in a 10 m highly nonlinear fiber using a sampling pulse source with a sampling pulse peak power of only 16 W. The sampling performance was evaluated in terms of sensitivity, temporal resolution and optical bandwidth with respect to fiber length, sampling pulse source wavelength offset from the zero-dispersion wavelength of the highly nonlinear fiber, sampling pulse peak power and walk-off due to chromatic dispersion. We also present a summary of the available methods to achieve polarization-independent optical sampling.
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| 4. |
- Caputa, Peter, 1973-
(författare)
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Design of efficient high-speed on-chip global interconnects
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of integrated circuits is continuously moving towards a System-on Chip realization where global interconnects, connecting circuit blocks separated by a long distance, have been considered a showstopper for process scaling due to their RC-delays. Our knowledge today is that high-speed interconnects must be described by models which include not only R and C, but also inductance and skin effect. One might think that this will make the situation worse, but we show that it is not so.In this thesis, we investigate the relevance of inductance in interconnect models and propose a new scheme for global interconnects based on the utilization of microstrip lines using two upper-level metal layers, one thicker layer for wires and one for a return ground plane. We are concerned with key performance measures such as data delay, maximum data-rate, crosstalk, edge-rates and power dissipation. Using our approach, we show that well-designed, highly lossy, long interconnects may show reasonable delays of the order of twice the delay compared to the velocity of light delay, and allow high data rates disconnected from total delay through wave pipelining. To demonstrate the feasibility of the proposed concept, we have designed and fabricated a test chip carrying a 5 mm long global communication link. Measurements show that we can achieve 3 Gb/s/wire over this 5 mm long, repeaterless on-chip bus implemented in a standard 0.18 µm CMOS process, achieving a signal velocity of 1/3 of the velocity of light in vacuum.In the context of technology scaling, there is a tendency for interconnects to dominate chip power dissipation due to their large total capacitance. In this thesis we address the problem of interconnect power dissipation by proposing and analyzing a transition energy cost model aimed for efficient power estimation of performance-critical buses. The model, which includes properties that closely capture effects present in high performance VLSI buses, can be used to more accurately determine energy benefits of e.g. transition coding of bus topologies. We further show a power optimization scheme based on appropriate choice of reduced voltage swing of the interconnect and scaling of receiver amplifier. Finally, the power saving impact of swing reduction in combination with a sense-amplifying flip-flop receiver is shown on a cache bus architecture used in industry.
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| 7. |
- Karlsson, Anne-Li, et al.
(författare)
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Bet v 1 homologues in strawberry identified as IgE-binding proteins and presumptive allergens
- 2004
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Ingår i: Allergy. - : Wiley. - 1398-9995 .- 0105-4538. ; 59:12, s. 1277-1284
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Tidskriftsartikel (refereegranskat)abstract
- Background: No strawberry allergen has so far been identified and characterized. Methods: Serum samples were collected from patients with a suggestive case history of adverse reactions to strawberry and other fruits. Extracts from fresh and frozen strawberries were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting and mass spectrometry. Patient blood samples were analysed for inhibition of IgE binding and basophil degranulation. Results: Several IgE-binding proteins could be detected. In more than half of the patient sera, a 20/18-kDa doublet band was observed in Western blotting. These two bands were excised and analysed by mass spectrometry showing the presence of proteins belonging to the Bet v 1 family of allergens. Inhibition of the IgE binding to the 20/18-kDa doublet was obtained by addition of two recombinantly expressed allergens belonging to the Bet v 1 family (Bet v 1 and Mal d 1) and strawberry protein extract. In a cell-based assay of patient blood samples, basophil degranulation could be induced by strawberry protein extract and by Bet v 1 and Mal d 1. Conclusions: We conclude that strawberry homologues to Bet v 1 may be allergens of importance for adverse reactions to strawberry.
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| 8. |
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| 9. |
- Lapointe, Jacques, et al.
(författare)
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Gene expression profiling identifies clinically relevant subtypes of prostate cancer
- 2004
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 101:3, s. 811-816
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Tidskriftsartikel (refereegranskat)abstract
- Prostate cancer, a leading cause of cancer death, displays a broad range of clinical behavior from relatively indolent to aggressive metastatic disease. To explore potential molecular variation underlying this clinical heterogeneity, we profiled gene expression in 62 primary prostate tumors, as well as 41 normal prostate specimens and nine lymph node metastases, using cDNA microarrays containing ≈26,000 genes. Unsupervised hierarchical clustering readily distinguished tumors from normal samples, and further identified three subclasses of prostate tumors based on distinct patterns of gene expression. High-grade and advanced stage tumors, as well as tumors associated with recurrence, were disproportionately represented among two of the three subtypes, one of which also included most lymph node metastases. To further characterize the clinical relevance of tumor subtypes, we evaluated as surrogate markers two genes differentially expressed among tumor subgroups by using immunohistochemistry on tissue microarrays representing an independent set of 225 prostate tumors. Positive staining for MUC1, a gene highly expressed in the subgroups with "aggressive" clinicopathological features, was associated with an elevated risk of recurrence (P = 0.003), whereas strong staining for AZGP1, a gene highly expressed in the other subgroup, was associated with a decreased risk of recurrence (P = 0.0008). In multivariate analysis, MUC1 and AZGP1 staining were strong predictors of tumor recurrence independent of tumor grade, stage, and preoperative prostate-specific antigen levels. Our results suggest that prostate tumors can be usefully classified according to their gene expression patterns, and these tumor subtypes may provide a basis for improved prognostication and treatment stratification.
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| 10. |
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