Squelched Galaxies and Dark Halos

There is accumulating evidence that the faint end of the galaxy luminosity function might be very different in different locations. The luminosity function might be rising in rich clusters and flat or declining in regions of low density. If galaxies form according to the model of hierarchical clustering then there should be many small halos compared to the number of big halos. If this theory is valid then there must be a mechanism that eliminates at least the visible component of galaxies in low density regions. A plausible mechanism is photoionization of the intergalactic medium at a time before the epoch that most dwarf galaxies form in low density regions but after the epoch of formation for similar systems that ultimately end up in rich clusters. The dynamical timescales are found to accommodate this hypothesis in a flat universe with Omega_m < 0.4. If small halos exist but simply cannot be located because they have never become the sites of significant star formation, they still might have dynamical manifestations. These manifestations are hard to identify in normal groups of galaxies because small halos do not make a significant contribution to the global mass budget. However, it could be entertained that there are clusters of halos where there are only small systems, clusters that are at the low mass end of the hierarchical tree. There may be places where only a few small galaxies managed to form, enough for us to identify and use as test probes of the potential. It turns out that such environments might be common. Four probable groups of dwarfs are identified within 5 Mpc and the assumption they are gravitationally bound suggests M/L_B ~ 300 - 1200 M_sun/L_sun, 6 +/- factor 2 times higher than typical values for groups with luminous galaxies.Comment: Accepted ApJ 569, (April 20), 2002, 12 pages, 6 figures, 1 tabl

Academic attainment and special educational needs in extremely preterm children at 11 years of age : the EPICure Study

Aim: To assess academic attainment and special educational needs (SEN) in extremely preterm (EP) children in middle childhood. Methods: Of 307 EP (=25 weeks) survivors born in the UK and Ireland in 1995, 219 (71%) were re-assessed at 11 years, with a comparison group of 153 classmates born at term, using standardised tests of cognitive ability and academic attainment and teacher reports of school performance and special educational needs (SEN). Multiple imputation was used to correct for selective dropout. Results: EP children had significantly lower scores than classmates for cognitive ability (-20 points; 95%CI: -23,-17), reading (-18 points; -22,-15) and mathematics (-27 points; -31,-23). Twenty-nine (13%) EP children attended special school. In mainstream schools, 105 (57%) EP children had SEN (OR: 10; 6, 18) and 103 (55%) required SEN resource provision (OR: 10; 5, 18). Teachers rated 50% of EP children with attainment below the average range compared with 5% of classmates (OR: 18; CI: 8, 41). EP children who are entered for mainstream education an academic year early due to preterm birth had similar academic attainment but required more SEN support (OR: 2; 1.1,3.8). Conclusions: EP survivors remain at high risk for learning impairments and poor academic attainment in middle childhood. A significant proportion require full-time specialist education and over half of those attending mainstream schools require additional health or educational resources in order to access the national curriculum. The prevalence and impact of SEN is likely to increase as these children approach the transition to secondary school. -------------------------------------------------------------------------------

The Relationship Between MR Demonstration of Extramural Venous Invasion and Nodal Disease in Rectal Cancer

© 2008 Libertas Academica Ltd. All rights reserved.Results: Compared with histology, an MR score of >2 was found to have 100% sensitivity (95% CI: 77%–100%) and 89% specificity (95% CI: 79%–96%) in identifying EMVI involving veins >3 mm in diameter. An EMVI score of >2 was had a sensitivity of 56% (95% CI: 30%–80%) and specificity of 81% (95% CI: 69%–90%) for identifying patients with stage N2 disease.Conclusions: EMVI score of >2 on T2-weighted MR imaging has a high sensitivity and specificity for histopathologically proven extramural venous invasion involving venules ≥3 mm in diameter. However, EMVI scores have only moderate sensitivity in the predicting nodal involvement.Purpose: To investigate the relationship between extramural venous invasion (EMVI) detected at T2-weighted MRI and nodal disease rectal cancer compared with histopathology.Materials and Methods: The MR imaging of 79 consecutive patients with rectal cancer who underwent primary rectal surgery without neoadjuvant treatment were reviewed. MR images were scored by an expert radiologist for the presence and degree of EMVI using a five point scale blinded to pathological findings. Receiver operating characteristic curve analyses were performed to determine the sensitivity and specificity of MRI scoring in predicting EMVI and nodal disease at histopathology

Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves

In-situ, device level measurement of thermal mag-noise spectral linewidths in 60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine the intrinsic Gilbert damping for both magnetic layers. It is shown that careful alignment at a "magic-angle" between free and reference layer static equilibrium magnetization can allow direct measurement of the broadband intrinsic thermal spectra in the virtual absence of spin-torque effects which otherwise grossly distort the spectral line shapes and require linewidth extrapolations to zero current (which are nonetheless also shown to agree well with the direct method). The experimental magic-angle spectra are shown to be in good qualitative and quantitative agreement with both macrospin calculations and micromagnetic eigenmode analysis. Despite similar composition and thickness, it is repeatedly found that the IrMn exchange pinned reference layer has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the free-layer (alpha ~ 0.01). It is argued that the large reference layer damping results from strong, off -resonant coupling to to lossy modes of an IrMn/ref couple, rather than commonly invoked two-magnon processes.Comment: 11 pages (2-column format), 12 figures. This work was presented at the 2010 Joint MMM-Intermag Conference (Washington, DC) as paper AB-01 (invited

Graded junction termination extensions for electronic devices

A graded junction termination extension in a silicon carbide (SiC) semiconductor device and method of its fabrication using ion implementation techniques is provided for high power devices. The properties of silicon carbide (SiC) make this wide band gap semiconductor a promising material for high power devices. This potential is demonstrated in various devices such as p-n diodes, Schottky diodes, bipolar junction transistors, thyristors, etc. These devices require adequate and affordable termination techniques to reduce leakage current and increase breakdown voltage in order to maximize power handling capabilities. The graded junction termination extension disclosed is effective, self-aligned, and simplifies the implementation process