Exact hybrid Vlasov equilibria for sheared plasmas with in-plane and out-of-plane magnetic field.

The hybrid Vlasov-Maxwell system of equations is suitable to describe a magnetized plasma at scales on the order of or larger than proton kinetic scales. An exact stationary solution is presented by revisiting previous results with a uniform-density shear flow, directed either parallel or perpendicular to a uniform magnetic field, and by adapting the solution to the hybrid Vlasov-Maxwell model. A quantitative characterization of the equilibrium distribution function is provided by studying both analytically and numerically the temperature anisotropy and gyrotropy and the heat flux. In both cases, in the shear region, the velocity distribution significantly departs from local thermodynamical equilibrium. A comparison between the time behavior of the usual "fluidlike" equilibrium shifted Maxwellian and the exact stationary solutions is carried out by means of numerical simulations of the hybrid Vlasov-Maxwell equations. These hybrid equilibria can be employed as unperturbed states for numerous problems which involve sheared flows, such as the wave propagation in an inhomogeneous background and the onset of the Kelvin-Helmholtz instability.

Turbulence generation during the head-on collision of Alfvénic wave packets.

The description of the Moffatt and Parker problem recently revisited by O. Pezzi et al. [Astrophys. J. 834, 166 (2017)1538-435710.3847/1538-4357/834/2/166] is here extended by analyzing the features of the turbulence produced by the interaction of two colliding Alfvénic wave packets in a kinetic plasma. Although the approach based on the presence of linear modes features is still helpful in characterizing some low-energy fluctuations, other signatures, which go beyond the pure linear modes analysis, are recovered, such as the significant weakening of clear dispersion relations and the production of zero frequency fluctuations.

Diagnostic accuracy of 3-T magnetic resonance imaging with 3D T1 VIBE versus computer tomography in pars stress fracture of the lumbar spine.

OBJECTIVE: To compare the diagnostic accuracy of 3-T magnetic resonance imaging (MRI) with thin-slice 3D T1 VIBE sequence to 128-slice computer tomography (CT) in pars stress fractures of the lumbar spine. MATERIALS AND METHODS: 3-T MRI and CT of 24 patients involving 70 pars interarticularis were retrospectively reviewed by four blinded radiologists. The fracture morphology (complete, incomplete, or normal) was assessed on MRI and CT at different time points. Pars interarticularis bone marrow edema (present or absent) was also evaluated on MRI. RESULTS: In total, 14 complete fractures, 31 incomplete fractures and 25 normal pars were detected by CT. Bone marrow edema was seen in seven of the complete and 25 of the incomplete fractures. The overall sensitivity, specificity and accuracy of MRI in detecting fractures (complete and incomplete) were 97.7, 92.3, and 95.7 %, respectively. MRI was 100 % accurate in detecting complete fractures. For incomplete fractures, the sensitivity, specificity, and accuracy of MRI were 96.7, 92.0, and 94.6 %, respectively. CONCLUSIONS: 3-T MRI with thin-slice 3D T1 VIBE is 100 % accurate in diagnosing complete pars fractures and has excellent diagnostic ability in the detection and characterization of incomplete pars stress fractures compared to CT. MRI has the added advantages of detecting bone marrow edema and does not employ ionizing radiation.

Relation between conversion degree and cytotoxicity of a flowable bulk-fill and three conventional flowable resin-composites.

OBJECTIVE: The aim of this study is to evaluate if the cytotoxic effects of the Surefil SDR flow, bulk fill flowable composite resin and three conventional flowable materials (Venus Diamond Flow, Filtex Supreme XTE Flowable and Enamel plus HRi Flow) correlated with the conversion degree (DC); hardness and depth of cure are also assessed. MATERIALS AND METHODS: Disks of each materials--cured using LED lamp--are utilized to evaluate DC (by FT-IR technique), amount of leached monomers (by HPLC technique), hardness (by Vickers hardness tester) and cytotoxicity (by MTT test). RESULTS: All tested materials show light cytotoxic effects, independently from DC values. Both the latter parameter and the hardness, in fact, change in function of thickness and type of material. HPLC results show that the monomers amount leached from each specimen is influenced by thickness but it is always very low which justifies the absence of any cytotoxic effect. CONCLUSIONS: Our findings suggest that there are not statistically significant differences in cytotoxicity in all experimental conditions, notwithstanding the differences in hardness and in degree of conversion.

Effects of anisotropic thermal conductivity in magnetohydrodynamics simulations of a reversed-field pinch.

A compressible magnetohydrodynamics simulation of the reversed-field pinch is performed including anisotropic thermal conductivity. When the thermal conductivity is much larger in the direction parallel to the magnetic field than in the perpendicular direction, magnetic field lines become isothermal. As a consequence, as long as magnetic surfaces exist, a temperature distribution is observed displaying a hotter confined region, while an almost uniform temperature is produced when the magnetic field lines become chaotic. To include this effect in the numerical simulation, we use a multiple-time-scale analysis, which allows us to reproduce the effect of a large parallel thermal conductivity. The resulting temperature distribution is related to the existence of closed magnetic surfaces, as observed in experiments. The magnetic field is also affected by the presence of an anisotropic thermal conductivity.

Compressibility effects in the dynamics of the reversed-field pinch.

We study the reversed-field pinch through the numerical solution of the compressible magnetohydrodynamic equations. Two cases are investigated: In the first case the pressure is derived from an adiabatic condition, and in the second case the pressure equation includes heating terms due to resistivity and viscosity. In the adiabatic case a single helicity state is observed, and the reversed-field pinch configuration is formed for short time intervals and is finally lost. In the nonadiabatic case the system reaches a multiple helicity state, and the reversal parameter remains negative for a longer time. The results show the importance of compressibility in determining the large scale dynamics of the system.

Evolution of anisotropic turbulence in nonlinear magnetic reconnection.

The anisotropy properties of magnetohydrodynamic turbulence in a sheared magnetic field are analyzed through a three-dimensional numerical simulation that reproduces the linear and nonlinear stage of a tearing instability. Far from the current sheet, the energy spectrum develops perpendicularly to the local magnetic field, as in homogeneous configurations. Within the current sheet, the spectrum anisotropy is also affected by the structure of unstable modes. With increasing time, the configuration becomes more turbulent, the former effect disappears, and the energy cascade takes place perpendicularly to the local magnetic field. The local spectrum becomes increasingly anisotropic while the spatially integrated spectrum tends to isotropize. There is the possibility that these properties could be used to identify the nonlinear stage of magnetic reconnection in space and laboratory plasmas, as well as to identify the particle transport regime in the considered magnetic configuration.

Use of the one-legged hyperextension test and magnetic resonance imaging in the diagnosis of active spondylolysis.

BACKGROUND: Active spondylolysis is an acquired lesion in the pars interarticularis and is a common cause of low back pain in the young athlete. OBJECTIVES: To evaluate whether the one-legged hyperextension test can assist in the clinical detection of active spondylolysis and to determine whether magnetic resonance imaging (MRI) is equivalent to the clinical gold standard of bone scintigraphy and computed tomography in the radiological diagnosis of this condition. METHODS: A prospective cohort design was used. Young active subjects with low back pain were recruited. Outcome measures included clinical assessment (one-legged hyperextension test) and radiological investigations including bone scintigraphy (with single photon emission computed tomography (SPECT)) and MRI. Computed tomography was performed if bone scintigraphy was positive. RESULTS: Seventy one subjects were recruited. Fifty pars interarticulares in 39 subjects (55%) had evidence of active spondylolysis as defined by bone scintigraphy (with SPECT). Of these, 19 pars interarticulares in 14 subjects showed a fracture on computed tomography. The one-legged hyperextension test was neither sensitive nor specific for the detection of active spondylolysis. MRI revealed bone stress in 40 of the 50 pars interarticulares in which it was detected by bone scintigraphy (with SPECT), indicating reduced sensitivity in detecting bone stress compared with bone scintigraphy (p = 0.001). Conversely, MRI revealed 18 of the 19 pars interarticularis fractures detected by computed tomography, indicating concordance between imaging modalities (p = 0.345). There was a significant difference between MRI and the combination of bone scintigraphy (with SPECT)/computed tomography in the radiological visualisation of active spondylolysis (p = 0.002). CONCLUSIONS: These results suggest that there is a high rate of active spondylolysis in active athletes with low back pain. The one-legged hyperextension test is not useful in detecting active spondylolysis and should not be relied on to exclude the diagnosis. MRI is inferior to bone scintigraphy (with SPECT)/computed tomography. Bone scintigraphy (with SPECT) should remain the first-line investigation of active athletes with low back pain followed by limited computed tomography if bone scintigraphy is positive.

Mesenteric Castleman's disease: ultrasound, computed tomography and angiographic appearance.

The localized form of Castleman's disease is rare, and a mesenteric location is particularly unusual. A case of an asymptomatic young woman having the hyaline vascular type is presented and the ultrasound, CT and angiographic features of the condition are demonstrated.

Effects of entropy inhomogeneity on density-temperature correlation in solar wind.

Compressive fluctuations in solar wind slow speed streams are studied by means of a magnetohydrodynamics (MHD) model, which represents the plasma in the vicinity of the heliospheric current sheet. The model contains a current sheet, as well as density and temperature variations, corresponding to a large scale modulation of the specific entropy. Alfvénic fluctuations are initially superimposed on the background equilibrium and compressive fluctuations are consequently generated during the time evolution. The resulting correlation between density and temperature fluctuations at various spatial scales is interpreted in terms of both generation of magnetosonic fluctuations and of an "entropy cascade." The latter phenomenon arises as a consequence of the interaction between the MHD turbulence and the underlying large scale entropy structure. In particular, it is responsible for anticorrelated density and temperature fluctuations detected at various scales. The results of the model are compared with the proton density-temperature correlation calculated during several crossings of solar wind slow speed streams by the Helios spacecraft. The model reproduces to a good extent the main observed features, in particular the dependence of the correlation coefficient on location (close to or far from the current sheet) and on the fluctuation scale. The results show that large scale inhomogeneities, in particular, that of specific entropy, are important ingredients in the dynamics of the MHD turbulence in slow speed streams.

[Ambulatory angiologic diagnosis using the Doppler c.w. (continuous wave) method]. / Diagnostica angiologica ambulatoriale nel territorio con Doppler c.w.

A one year clinical activity of instrumental angiological diagnostics (doppler c.w. examinations) was evaluated and analysed. 970 outpatient continuous wave doppler have been performed: 37% examinations of epiaortic vessels (TSA), 31% examinations of lower limb veins, 28% examinations of lower limbs arteries. The question has been inappropriate (normal exam) in 81% of TSA, in 67% of AIA and in 52% of AIV. The authors think that the reasons for these results are a large misinformation from the physicians postulant and a consequent abuse of the instrumental method. It's therefore necessary to put a clinical filter to regulate the access to the instrumental (high technological) examinations, too often unnecessary.

[Cardiovascular adjustments in hypertensive patients. An echocardiographic study]. / Adattamenti cardiovascolari in ipertesi. Studio ecocardiografico.

Echocardiography was used to asses parameters of cardiovascular function in order to identify the main cardiac adjustment mechanisms to arterial hypertension. In addition to morphological parameters of septal and parietal thickness and diameter, telesystolic (Ses) and telediastolic (Spk) stress, EF, Vcfm, the index of left ventricular mass (ILVM), hypertrophy ratio (h/r), contractility index (Do), peripheral resistances (RPT) and Tarazi's index (SAC) were evaluated. In comparison to control subjects, higher levels of PwTs, h/r, SAC, RPT and ILVM (at the limit of significance) were found in hypertensive patients, which were reflected by higher Spk and Do values. From the further analysis of data to identify patients with signs of left ventricular hypertrophy (h/r greater than 0.40 and/or ILVM greater than 140) it was concluded that the hypertrophy ratio (h/r) is the functional parameter which most closely reveals the type of myocardial adjustment. Irrespective of absolute values of ILVM, the adequacy of myocardial hypertrophy to the dimensions of the cavity is accompanied by the normalisation of stress and the return of Do values close to normal levels. Hearts with low h/r those with the highest stress levels, as well as preesting the lowest EF and the highest Do values.

[Endoscopic excision of a pin implanted in the 3d portion of the duodenum]. / Rimozione endoscopica di spillo infisso in IIIa porzione duodenale.

The Authors, while presenting a case of endoscopic extraction of a foreign body fixed in the duodenum, underline the value of operative endoscopy, which, going beyond the limits of a exclusively diagnostic technique, is intended as a first choice therapeutic procedure to be always carried out, leaving to surgery the treatment of the most complicated cases and those where the endoscopic attempt fails.