Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field.

The shaping of astrophysical outflows into bright, dense, and collimated jets due to magnetic pressure is here investigated using laboratory experiments. Here we look at the impact on jet collimation of a misalignment between the outflow, as it stems from the source, and the magnetic field. For small misalignments, a magnetic nozzle forms and redirects the outflow in a collimated jet. For growing misalignments, this nozzle becomes increasingly asymmetric, disrupting jet formation. Our results thus suggest outflow/magnetic field misalignment to be a plausible key process regulating jet collimation in a variety of objects from our Sun's outflows to extragalatic jets. Furthermore, they provide a possible interpretation for the observed structuring of astrophysical jets. Jet modulation could be interpreted as the signature of changes over time in the outflow/ambient field angle, and the change in the direction of the jet could be the signature of changes in the direction of the ambient field.

The need of appropriate brain SPECT templates for SPM comparisons.

AIM: Statistical parametric mapping (SPM) is used worldwide to compare brain perfusion single photon emission computed tomography (SPECT) data. The default template within the SPM package used for SPECT image normalization includes images of a group of healthy subjects studied with [(99m)Tc]HMPAO. Since [(99m)Tc]HMPAO and [(99m)Tc]ECD have shown to distribute differently in SPECT studies, we formulated the hypothesis that comparing set of [(99m)Tc]ECD data normalized by means of a [(99m)Tc]HMPAO template may lead to incorrect results. METHODS: A customized [(99m)Tc]ECD template was built with SPECT and magnetic resonance imaging (MRI) images of 22 neurologically healthy women. Then, two sets of subjects, i.e. a group of patients with very early Alzheimer's disease (eAD) and a matched control group, studied by means of [(99m)Tc]ECD SPECT, were chosen for comparisons. The same statistical approach (t-test between eAD patients and controls and correlation analysis between brain SPECT and a cognitive score) was applied twice, i.e. after normalization with either the default [(99m)Tc]HMPAO template or the customized [(99m)Tc]ECD template. RESULTS: In the comparison between eAD and controls, a cluster of difference in the posterior cingulate gyrus of both hemispheres was only highlighted when using the customized [(99m)Tc]ECD template, but was missed when using the default [(99m)Tc]HMPAO template. In the correlation between brain perfusion and a cognitive score, the significant cluster was more significant and far more extended, also including the right superior temporal gyrus, using the customized [(99m)Tc]ECD template than using the default [(99m)Tc]HMPAO template. CONCLUSION: These data suggest the need of customized, radiopharmaceutical-matched SPECT templates to be used within the SPM package. The present customized [(99m)Tc]ECD template is now freely available on the web.

Kelvin-Helmholtz instability for relativistic fluids.

We reexamine the stability of an interface separating two nonmagnetized relativistic fluids in relative motion, showing that, in an appropriate reference frame, it is possible to find analytic solutions to the dispersion relation. Moreover, we show that the critical value of the Mach number, introduced by compressibility, is unchanged from the nonrelativistic case if we redefine the Mach number as M= [beta/ (1- beta(2) )(1/2) ] [ beta(s) / (1- beta(2)(s) )(1/2) ](-1) , where beta and beta(s) are, respectively, the speed of the fluid and the speed of sound (in units of the speed of light).

Public health response actions and the use of emergency operations centers.

In the wake of 11 September 2001, many public health agencies are reassessing their institutional capabilities and procedures to respond to mass-casualty incidents involving weapons of mass destruction. Prior to the fall of 2001, planning by the public health and other sectors addressed more conventional or naturally occurring events such as earthquakes, hurricanes, tornados, and chemical spills, although attacks with weapons of mass destruction were a growing concern. While the nature of natural versus intentional events differs, the management and coordination of response activities to them follows the same incident command system. A major lesson learned during the response operations to the 11 September 2001 attacks in New York City was the value of disaster planning, conducting exercises, and developing relationships among the various response agencies. Although New York City's physical Emergency Operations Center (EOC) at 7 World Trade Center was destroyed in the attack, the medical and health response community was able to react effectively to the possibility of mass casualties as well as to the more usual needs. This was enabled by the pre-existing relationships that had been developed between city, state, federal, and non-governmental agencies while planning and exercising for such events and their aftermaths.