Figure 2Human apo E4 expression by astrocytes suppresses Aβ deposition, as assessed by anti-Aβ immunostaining in APP V717F+/-mice at 39 weeks of age. APP V717F+/-, mouse apo E +/+ animals had numerous hippocampal and some cortical Aβ-IR deposits by 39 weeks of age (a and b). APP V717F+/-, apo E -/-animals had less Aβ-IR deposits than those expressing mouse apo E; however, there was still a significant amount of deposition in all animals assessed. In addition, the hippocampal Aβ that was present in apo E -/-mice was in a different distribution, with more Aβ immunoreactivity in the hilus of the dentate gyrus and none in the cortex (c and d). In APP V717F+/-, apo E4 +/-line 22 animals, hippocampal Aβ immunoreactivity was completely absent in most animals (e and f). Scale bar: 60 µm for b, d, and f; 150 µm for a, c, and e. Aβ, amyloid β; APP, amyloid precursor protein; IR, immunoreactive.

Turbulence is ubiquitous in many astrophysical systems like galaxies, galaxy clusters and possibly even the filaments in the intergalactic medium. We study fluctuation dynamo action in turbulent systems focusing on one observational signature; the random Faraday rotation measure (RM) from radio emission of background sources seen through the intermittent magnetic field generated by such a dynamo. We simulate the fluctuation dynamo in periodic boxes up to resolutions of 512 3 , with varying fluid and magnetic Reynolds numbers, and measure the resulting random RMs. We show that, even though the magnetic field generated is intermittent, it still allows for contributions to the RM to be significant. When the dynamo saturates, the rms value of RM is of order 40-50% of the value expected in a model where fields of strength B rms uniformly fill cells of the largest turbulent eddy but are randomly oriented from one cell to another. This level of RM dispersion obtains across different values of magnetic Reynolds number and Prandtl number explored. We also use the random RMs to probe the structure of the generated fields to distinguish the contribution from intense and diffuse field regions. We find that the strong field regions (say with B > 2B rms ) contribute only of order 15-20% to the RM. Thus rare structures do not dominate the RM; rather the general 'sea' of volume filling fluctuating fields are the dominant contributors. We also show that the magnetic integral scale, L int , which is directly related to the RM dispersion, increases in all the runs, as Lorentz forces become important to saturate the dynamo. It appears that due to the ordering effect of the Lorentz forces, L int of the saturated field tends to a modest fraction, 1/2 − 1/3 of the integral scale of the velocity field, for all our runs. These results are then applied to discuss the Faraday rotation signatures of fluctuation dynamo generated fields in young galaxies, galaxy clusters and intergalactic filaments.

Undergraduate medical studentsChoice of specialty a b s t r a c t Background: Empathy is essentially a desirable quality among clinicians and can be developed during medical education. Studies from outside India have shown that higher empathy is related to better competency and choice of specialty may be related to empathy levels in them. Change in empathy levels among undergraduate medical students with progressive training has been often ascribed to reasons such as curriculum content, timing of clinical rotations. Gender differences in empathy levels also vary among different countries. Since many of such factors differ in India there is a need therefore to understand empathy and its correlates among medical students in India.Method: A cross sectional study was undertaken in a large medical college among the undergraduates of first, third, fifth, seventh and ninth semesters to measure their empathy levels. The evaluation was done using the Jefferson's Scale for Physician's Empathy-Student version.Results: The study revealed highest empathy at entry level and a significant fall by seventh semester (p ¼ 0.002). Female students had significantly higher empathy levels than male students (p ¼ 0.012) across all semesters. The variance in empathy scores according specialty chosen is not statistically significant (p ¼ 0.2468). Conclusion:The progressive decline in empathy levels with years in medical college here is seen much later than in western studies. Female students are more empathetic than male students. The relation of mean empathy scores and choice of specialty is inconclusive and at variance from other studies.ª 2014, Armed Forces Medical Services (AFMS). All rights reserved.* Corresponding author. Tel.: þ91 9657167900 (mobile). E-mail address: sribuj@yahoo.com (R. Shashikumar).Available online at www.sciencedirect.com ScienceDirect journal homepage: w ww.el sevier.com/locate/mjafi m e d i c a l j o u r n a l a r m e d f o r c e s i n d i a 7 0 ( 2 0 1 4 ) 1 7 9 e1 8 5

Magnetic energy transfer from small to large scales due to successive magnetic island coalescence is investigated. A solvable analytical model is introduced and shown to correctly capture the evolution of the main quantities of interest, as borne out by numerical simulations. Magnetic reconnection is identified as the key mechanism enabling the inverse transfer, and setting its properties: magnetic energy decays ast −1 , wheret is time normalized to the (appropriately defined) reconnection timescale; and the correlation length of the field grows ast 1/2 . The magnetic energy spectrum is self-similar, and evolves as ∝t −3/2 k −2 , where the k-dependence is imparted by the formation of thin current sheets.

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We use high resolution direct numerical simulations (DNS) to show that helical turbulence can generate significant large-scale fields even in the presence of strong smallscale dynamo action. During the kinematic stage, the unified large/small-scale dynamo grows fields with a shape-invariant eigenfunction, with most power peaked at small scales or large k, as in Subramanian & Brandenburg (2014). Nevertheless, the largescale field can be clearly detected as an excess power at small k in the negatively polarized component of the energy spectrum for a forcing with positively polarized waves. Its strength B, relative to the total rms field B rms , decreases with increasing magnetic Reynolds number, Re M . However, as the Lorentz force becomes important, the field generated by the unified dynamo orders itself by saturating on successively larger scales. The magnetic integral scale for the positively polarized waves, characterizing the small-scale field, increases significantly from the kinematic stage to saturation. This implies that the small-scale field becomes as coherent as possible for a given forcing scale, which averts the Re M -dependent quenching of B/B rms . These results are obtained for 1024 3 DNS with magnetic Prandtl numbers of Pr M = 0.1 and 10. For Pr M = 0.1, B/B rms grows from about 0.04 to about 0.4 at saturation, aided in the final stages by helicity dissipation. For Pr M = 10, B/B rms grows from much less than 0.01 to values of the order the 0.2. Our results confirm that there is a unified large/small-scale dynamo in helical turbulence.

Fluctuation dynamos are generic to astrophysical systems. The only analytical model of the fluctuation dynamo is the Kazantsev model which assumes a velocity field that is delta-correlated in time. We derive a generalized model of fluctuation dynamos with finite correlation time, τ , using renovating flows. For τ → 0, we recover the standard Kazantsev equation for the evolution of longitudinal magnetic correlation, M L . To the next order in τ , the generalized equation involves third and fourth spatial derivatives of M L . It can be recast to one with at most second derivatives of M L using the Landau-Lifschitz approach. Remarkably, we then find that the magnetic power spectrum remains the Kazantsev spectrum of M(k) ∝ k 3/2 , in the large k limit, independent of τ .

Observations of Faraday rotation through high-redshift galaxies have revealed that they host coherent magnetic fields that are of comparable strengths to those observed in nearby galaxies. These fields could be generated by fluctuation dynamos. We use idealized numerical simulations of such dynamos in forced compressible turbulence up to rms Mach number of 2.4 to probe the resulting rotation measure (RM) and the degree of coherence of the magnetic field. We obtain rms values of RM at dynamo saturation of the order of 45 -55 per cent of the value expected in a model where fields are assumed to be coherent on the forcing scale of turbulence. We show that the dominant contribution to the RM in subsonic and transonic cases comes from the general sea of volume filling fields, rather than from the rarer structures. However, in the supersonic case, strong field regions as well as moderately overdense regions contribute significantly. Our results can account for the observed RMs in young galaxies.