22,297 research outputs found
Appearance of the canine meninges in subtraction magnetic resonance images
The canine meninges are not visible as discrete structures in noncontrast magnetic resonance (MR) images, and are incompletely visualized in T1âweighted, postgadolinium images, reportedly appearing as short, thin curvilinear segments with minimal enhancement. Subtraction imaging facilitates detection of enhancement of tissues, hence may increase the conspicuity of meninges. The aim of the present study was to describe qualitatively the appearance of canine meninges in subtraction MR images obtained using a dynamic technique. Images were reviewed of 10 consecutive dogs that had dynamic preâ and postgadolinium T1W imaging of the brain that was interpreted as normal, and had normal cerebrospinal fluid. Imageâanatomic correlation was facilitated by dissection and histologic examination of two canine cadavers. Meningeal enhancement was relatively inconspicuous in postgadolinium T1âweighted images, but was clearly visible in subtraction images of all dogs. Enhancement was visible as faint, smallârounded foci compatible with vessels seen end on within the sulci, a series of larger rounded foci compatible with vessels of variable caliber on the dorsal aspect of the cerebral cortex, and a continuous thin zone of moderate enhancement around the brain. Superimposition of colorâencoded subtraction images on pregadolinium T1â and T2âweighted images facilitated localization of the origin of enhancement, which appeared to be predominantly dural, with relatively few leptomeningeal structures visible. Dynamic subtraction MR imaging should be considered for inclusion in clinical brain MR protocols because of the possibility that its use may increase sensitivity for lesions affecting the meninges
Secondary pattern computation of an arbitrarily shaped main reflector
The secondary pattern of a perfectly conducting offset main reflector being illuminated by a point feed at an arbitrary location was studied. The method of analysis is based upon the application of the Fast Fourier Transform (FFT) to the aperture fields obtained using geometrical optics (GO) and geometrical theory of diffraction (GTD). Key features of the reflector surface is completely arbitrary, the incident field from the feed is most general with arbitrary polarization and location, and the edge diffraction is calculated by either UAT or by UTD. Comparison of this technique for an offset parabolic reflector with the Jacobi-Bessel and Fourier-Bessel techniques shows good agreement. Near field, far field, and scan data of a large reflector are presented
Cryptococcus neoformans chitin synthase 3 plays a critical role in dampening host inflammatory responses
Cryptococcus neoformans is the most common disseminated fungal pathogen in AIDS patients, resulting in âŒ200,000 deaths each year. There is a pressing need for new treatments for this infection, as current antifungal therapy is hampered by toxicity and/or the inability of the hostâs immune system to aid in resolution of the disease. An ideal target for new therapies is the fungal cell wall. The cryptococcal cell wall is different from the cell walls of many other pathogenic fungi in that it contains chitosan. Strains that have decreased chitosan are less pathogenic and strains that are deficient in chitosan are avirulent and can induce protective responses. In this study, we investigated the host responses to a chs3Î strain, a chitosan-deficient strain, and found that mice inoculated with the chs3Î strain all died within 36âh and that death was associated with an aberrant hyperinflammatory immune response driven by neutrophils, indicating that chitosan is critical in modulating the immune response to Cryptococcus.Cryptococcus neoformans infections are significant causes of morbidity and mortality among AIDS patients and the third most common invasive fungal infection in organ transplant recipients. One of the main interfaces between the fungus and the host is the fungal cell wall. The cryptococcal cell wall is unusual among human-pathogenic fungi in that the chitin is predominantly deacetylated to chitosan. Chitosan-deficient strains of C. neoformans were found to be avirulent and rapidly cleared from the murine lung. Moreover, infection with a chitosan-deficient C. neoformans strain lacking three chitin deacetylases (cda1Îcda2Îcda3Î) was found to confer protective immunity to a subsequent challenge with a virulent wild-type counterpart. In addition to the chitin deacetylases, it was previously shown that chitin synthase 3 (Chs3) is also essential for chitin deacetylase-mediated formation of chitosan. Mice inoculated with the chs3Î strain at a dose previously shown to induce protection with the cda1Îcda2Îcda3Î strain die within 36âh after installation of the organism. Mortality was not dependent on viable fungi, as mice inoculated with a heat-killed preparation of the chs3Î strain died at the same rate as mice inoculated with a live chs3Î strain, suggesting that the rapid onset of death was host mediated, likely caused by an overexuberant immune response. Histology, cytokine profiling, and flow cytometry indicate a massive neutrophil influx in the mice inoculated with the chs3Î strain. Mice depleted of neutrophils survived chs3Î inoculation, indicating that death was neutrophil mediated. Altogether, these studies lead us to conclude that Chs3, along with chitosan, plays critical roles in dampening cryptococcus-induced host inflammatory responses
Perturbative Computation of Glueball Superpotentials
Using N=1 superspace techniques in four dimensions we show how to
perturbatively compute the superpotential generated for the glueball superfield
upon integrating out massive charged fields. The technique applies to arbitrary
gauge groups and representations. Moreover we show that for U(N) gauge theories
admitting a large N expansion the computation dramatically simplifies and we
prove the validity of the recently proposed recipe for computation of this
quantity in terms of planar diagrams of matrix integrals.Comment: 15 Pages, 2 Figure
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Early time dynamics of laser-ablated silicon using ultrafast grazing incidence X-ray scattering
Controlling the morphology of laser-derived nanomaterials is dependent on developing a better understanding of the particle nucleation dynamics in the ablation plume. Here, we utilize the femtosecond-length pulses from an x-ray free electron laser to perform time-resolved grazing incidence x-ray scattering measurements on a laser-produced silicon plasma plume. At 20 ps we observe a dramatic increase in the scattering amplitude at small scattering vectors, which we attribute to incipient formation of liquid silicon droplets. These results demonstrate the utility of XFELs as a tool for characterizing the formation dynamics of nanomaterials in laser-produced plasma plumes on ultrafast timescales
Implementing Unitarity in Perturbation Theory
Unitarity cannot be perserved order by order in ordinary perturbation theory
because the constraint UU^\dagger=\1 is nonlinear. However, the corresponding
constraint for , being , is linear so it can be
maintained in every order in a perturbative expansion of . The perturbative
expansion of may be considered as a non-abelian generalization of the
linked-cluster expansion in probability theory and in statistical mechanics,
and possesses similar advantages resulting from separating the short-range
correlations from long-range effects. This point is illustrated in two QCD
examples, in which delicate cancellations encountered in summing Feynman
diagrams of are avoided when they are calculated via the perturbative expansion
of . Applications to other problems are briefly discussed.Comment: to appear in Phys. Rev.
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