SUMMARY
Recruitment of polymorphonuclear leucocytes (PMN) across the intestinal epithelium is dependent on specific adhesion molecules and chemoattractants diffusing from the intestinal lumen. The ...present understanding is that in response to fMLP, PMN migration across a T84 colon carcinoma monolayer is dependent on the β2 integrin, Mac‐1 (CD11b/CD18). To further understand PMN transepithelial migration, we sought to determine whether migration to C5a, IL‐8 and LTB4 was similarly Mac‐1‐, or even CD18‐dependent. T84 epithelial cell monolayers growing on Transwell filters were used in combination with radiolabelled peripheral blood PMN. The number of migrated PMN was established by the amount of radioactivity recovered from the well after the migration period. Monoclonal antibodies were used to block integrin function. Whereas essentially all migration to fMLP across T84 monolayers was prevented by anti‐CD18 antibody, significant migration to C5a, IL‐8 or LTB4 persisted despite anti‐CD18 antibody, indicating PMN are capable of β2 integrin‐independent transepithelial migration. An antibody to CD11b but not CD11a blocked migration to an extent similar as with anti‐CD18. CD18‐independent PMN migration to C5a occurred only in the basolateral‐to‐apical direction across epithelial cells. Co‐stimulation of PMN with C5a and fMLP or IL‐8 plus LTB4 and fMLP still resulted in CD18‐independent migration. Thus CD18 use during PMN migration across this model epithelium is a function of the chemoattractant inducing migration. The finding of CD18‐independent migration mechanisms needs to be considered when developing antiadhesion molecule strategies to reduce or reverse intestinal inflammation.
Combined X-ray synchrotron and inverse-Compton γ-ray observations of pulsar wind nebulae (PWN) may help to elucidate the processes of acceleration and energy loss in these systems. In particular, ...such observations provide constraints on the particle injection history and the magnetic field strength in these objects. The newly discovered TeV γ-ray source HESS J1718-385 has been proposed as the likely PWN of the high spin-down luminosity pulsar PSR J1718-3825. The absence of previous, sensitive X-ray measurements of this pulsar, and the unusual energy spectrum of the TeV source, motivated observations of this region with XMM-Newton. The data obtained reveal a hard-spectrum X-ray source at the position of PSR 1718-3825 and evidence of diffuse emission in the vicinity of the pulsar. We derive limits on the keV emission from the centroid of HESS J1718-385 and discuss the implications of these findings for the PWN nature of this object.
A three-dimensional developmental finite element model has been created to analyze load transmission pathways in the constrained carpus during static compressive loading. The bone geometry was ...extracted from an in vivo computed tomography scan using a combination of commercial and proprietary software. The complete geometry, including bone, cartilage, and ligament tissues, was compiled using a commercial finite element program. This model extends the state of biomechanical modeling by being the first to incorporate all eight carpal bones of the wrist and the related soft tissues in three dimensions. The model results indicate that cartilage material modulus and unconstrained carpal rotation have substantial impacts on the articular contact patterns and pressures.
This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS). Weekly ...light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4-2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis. For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares. More than 50% of the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects. Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks. Variable sources of the sample have weekly and 3-4 day bin light curves that can be described by 1/f(alpha) PDS, and show two kinds of gamma-ray variability: (1) rather constant baseline with sporadic flaring activity characterized by flatter PDS slopes resembling flickering and red noise with occasional intermittence and (2)-measured for a few blazars showing strong activity-complex and structured temporal profiles characterized by long-term memory and steeper PDS slopes, reflecting a random walk underlying mechanism. The average slope of the PDS of the brightest 22 FSRQs and of the 6 brightest BL Lacs is 1.5 and 1.7, respectively. The study of temporal profiles of well-resolved flares observed in the 10 brightest LBAS sources shows that they generally have symmetric profiles and that their total duration vary between 10 and 100 days. Results presented here can assist in source class recognition for unidentified sources and can serve as reference for more detailed analysis of the brightest gamma-ray blazars.
We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gammaray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB ...090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with E-peak = 3.9 +/- 0.3 MeV, which is the highest yet measured, and a hard power-law component with photon index -1.62 +/- 0.03 that dominates the emission below approximate to 20 keV and above approximate to 100 MeV. The onset of the high-energy spectral component appears to be delayed by similar to 0.1 s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5 s before the main pulse. During the prompt phase, the LAT detected a photon with energy 30.5(-2.6)(+5.8) GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, Gamma greater than or similar to 1200, using simple.. opacity arguments for this GRB at redshift z = 0.903 and a variability timescale on the order of tens of ms for the approximate to 100 keV-few MeV flux. Stricter high confidence estimates imply Gamma greater than or similar to 1000 and still require that the outflows powering short GRBs are at least as highly relativistic as those of long-duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton, external-shock synchrotron, and hadronic models are considered.
We present detailed analysis of two gamma-ray sources, 1FGL J1801.3-2322c and 1FGL J1800.5-2359c, that have been found toward the supernova remnant (SNR) W28 with the Large Area Telescope (LAT) on ...board the Fermi Gamma-ray Space Telescope. 1FGL J1801.3-2322c is found to be an extended source within the boundary of SNR W28, and to extensively overlap with the TeV gamma-ray source HESS J1801-233, which is associated with a dense molecular cloud interacting with the SNR. The gamma-ray spectrum measured with the LAT from 0.2 to 100 GeV can be described by a broken power-law function with a break at similar to 1 GeV and photon indices of 2.09 +/- 0.08 (stat) +/- 0.28 (sys) below the break and 2.74 +/- 0.06 (stat) +/- 0.09 (sys) above the break. Given the clear association between HESS J1801-233 and the shocked molecular cloud and a smoothly connected spectrum in the GeV-TeV band, we consider the origin of the gamma-ray emission in both GeV and TeV ranges to be the interaction between particles accelerated in the SNR and the molecular cloud. The decay of neutral pions produced in interactions between accelerated hadrons and dense molecular gas provides a reasonable explanation for the broadband gamma-ray spectrum. 1FGL J1800.5-2359c, located outside the southern boundary of SNR W28, cannot be resolved. An upper limit on the size of the gamma-ray emission was estimated to be similar to 16' using events above similar to 2 GeV under the assumption of a circular shape with uniform surface brightness. It appears to coincide with the TeV source HESS J1800-240B, which is considered to be associated with a dense molecular cloud that contains the ultra compact H II region W28A2 (G5.89-0.39). We found no significant gamma-ray emission in the LAT energy band at the positions of TeV sources HESS J1800-230A and HESS J1800-230C. The LAT data for HESS J1800-230A combined with the TeV data points indicate a spectral break between 10 GeV and 100 GeV.
The gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample LBAS) are investigated using Fermi-LAT data. Spectral properties hardness, curvature, and variability) established using a ...data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: flat spectrum radio quasars (FSRQs), low-synchrotron peaked BLLacs (LSP-BLLacs), intermediate-synchrotron peaked BLLacs (ISP-BLLacs), and high-synchrotron peaked BLLacs (HSP-BLLacs). The distribution of photon index G, obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the 6 months observing period is < 0.2-0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. This feature is also present for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source, respectively, a broken power law (BPL) gives the most acceptable of power law, BPL, and curved forms. The consequences of these findings are discussed.
This is the first of a series of papers aimed at characterizing the populations detected in the high-latitude sky of the Fermi-LAT survey. In this work, we focus on the intrinsic spectral and flux ...properties of the source sample. We show that when selection effects are properly taken into account, Fermi sources are on average steeper than previously found (e.g., in the bright source list) with an average photon index of 2.40 +/- 0.02 over the entire 0.1-100 GeV energy band. We confirm that flat spectrum radio quasars have steeper spectra than BL Lacertae objects with an average index of 2.48 +/- 0.02 versus 2.18 +/- 0.02. Using several methods, we build the deepest source count distribution at GeV energies, deriving that the intrinsic source (i.e., blazar) surface density at F-100 >= 10(-9) ph cm(2) s(-1) is 0.12(-0.02)(+0.03) deg(-2). The integration of the source count distribution yields that point sources contribute 16(+/- 1.8)% (+/- 7% systematic uncertainty) of the GeV isotropic diffuse background. At the fluxes currently reached by LAT, we can rule out the hypothesis that pointlike sources (i.e., blazars) produce a larger fraction of the diffuse emission.
PDF
