Hypertrophic pachymeningitis is extremely rare. It is a fibrosing inflammatory process which involves the dura mater, including the tentorium. Numerous pathological entities produce thickening of the pachymeninges, so that idiopathic hypertrophic pachymeningitis is a diagnosis of exclusion. We describe four patients with idiopathic hypertrophic pachymeningitis who had varied clinical presentation. Imaging studies revealed diffuse thickening of the pachymeninges; in one patient there was extensive dural sinus thrombosis. Since no identifiable cause was found, the cases were labelled as idiopathic.

Resonant excitation of terahertz (THz) radiation based on beating of two spatial-Gaussian lasers having different frequencies and wave numbers but the same electric field amplitudes is proposed in a spatially periodic density plasma in the presence of a static magnetic field applied perpendicular to the direction of propagation of the lasers. In this process, the ponderomotive force is developed with its components parallel and perpendicular to the direction of propagation of the lasers. This leads to a nonlinear oscillatory current that resonantly excites the THz radiation with the frequency of the order of the upper hybrid frequency. The contribution of magnetic field, laser beamwidth, and amplitude and periodicity of the density ripples is discussed for the efficient THz radiation generation. With the optimization of these parameters, the efficiency on the order of 10(-3) or larger can be achieved in the present scheme.

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We propose two super-Gaussian laser beams with frequency difference for obtaining more collimated terahertz (THz) radiation at a desired position based on their order/index and for enhancing the efficiency of the scheme by realizing stronger transient transverse current due to the spatial variation of their fields. For the laser intensity of ∼1014 W/cm2 and along with the application of a periodic density structure, a resonant excitation of the THz radiation is achieved together with the efficiency of scheme as ∼0.006.

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Optical emission from xenon plasma in a hollow cathode has been recorded over a wide range of wavelengths extending from vacuum ultraviolet to the visible band 100-590 nm. The cathode was operated in direct current discharge mode with a continuous flow of xenon ~13 cc min -1 at 70 Torr. A column of neutral xenon gas (~21.2 cm long) existed in-between the active plasma column (~1 cm long) source and the detector. The observed spectra show that strong Xe II and impurity (Ba, Al and Ca) lines are superimposed on a weak continuum. Xenon I lines have not been observed. A subsidiary broadened continuum band within the far vacuum ultraviolet range 100-200 nm supports the evidence that the emission due to the transitions by the excited molecular dimer/excimer species is also involved. In the present work, bremsstrahlung emission has been used to estimate the plasma electron temperature Te = 1.1 eV. The resulting electron density ne = 1014 cm-3 is then obtained using the Saha formulation for the ratio of the discrete lines. The radiative properties and the validity of the various plasma equilibrium models within the hollow cathode have also been discussed.

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The generation of terahertz (THz) radiation based on tunnel ionization of a gas jet is analytically investigated when two superposed short pulse lasers with finite initial phase difference are focused on to it after passing through an axicon. The phase difference between these two lasers plays an important role for the optimization of rate of ionization, evolution of plasma density, and subsequently the residual current due to dipole oscillations. The directionality of the emitted THz radiation can be controlled by tuning initial phase difference between the two laser pulses. Since a nonuniform plasma is produced during the tunnel ionization, the effect of radial variation in the electron density in the plasma channel is studied on the frequency of the emitted THz radiation and on its power. Higher power THz radiation is obtained for the higher fields of the lasers. With optimum initial phase of the laser envelope and the channel width, the mechanism seems to be much more efficient than some of the other mechanisms.