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Context. The solar corona is a template to understand stellar activity. The Sun is a moderately active star, and its corona differs from that of active stars: for instance, active stellar coronae have a double-peaked emission measure distribution $EM(T)$with a hot peak at $8{-}20$MK, while the non-flaring solar corona has one peak at $1{-}2$MK and, typically, much cooler plasma.

Aims. We investigate the spatial distribution of the physical and chemical properties of the hot X-ray emitting plasma of the supernova remnant IC 443, to derive important constraints on its ionization stage, on the progenitor supernova explosion, on the age of the remnant, and its physical association with a close pulsar wind nebula.

Aims. We provide a guideline to interpret the UltraViolet Coronograph Spectrometer (UVCS) emission lines (in particular O VI and Si XII) during shock wave propagation in the outer solar corona.

We present simultaneous high-temporal and high-spectral resolution observations of the nearby flare star CN Leo at optical and soft X-ray wavelengths. During our observing campaign a major flare occurred, raising the star's instantaneous energy output by almost three orders of magnitude. The flare shows the often observed impulsive behavior, with a rapid rise and slow decay in the optical and a broad soft X-ray maximum about 200 seconds after the optical flare peak. In addition to this usually encountered flare phenomenology we find, however, an extremely short ($\tau _{\rm dec} \approx 2$s) soft X-ray peak, which is very likely of thermal, rather than nonthermal nature and coincides temporally with the optical flare peak. While at hard X-ray energies nonthermal bursts are routinely observed on the Sun at flare onset, thermal soft X-ray bursts on time scales of seconds have never been observed in a solar, nor stellar context. Time-dependent, one-dimensional hydrodynamic modeling of this event requires an extremely short energy deposition time scale $\tau _{\rm dep}$of a few seconds to reconcile theory with observations, thus suggesting that we are witnessing the results of a coronal explosion on CN Leo. Thus the flare on CN Leo provides the opportunity to observationally study the physics of the long-sought “micro-flares” thought to be responsible for coronal heating.

Context.Weak flares are supposed to be an important heating agent of the outer layers of stellar atmospheres. However, due to instrumental limitations, only large X-ray flares have been studied in detail until now.

Context.The diagnostics of stellar flaring coronal loops have been so far largely based on the analysis of the decay phase.

Context.X-ray flares are common phenomena in pre-main sequence stars. Their analysis gives insights into the physics at work in young stellar coronae. The Orion Nebula Cluster offers a unique opportunity to study large samples of young low mass stars. This work is part of the ChandraOrion Ultradeep project (COUP), an ~10 day long X-ray observation of the Orion Nebula Cluster (ONC).

Aims.We investigate whether the morphology of bilateral supernova remnants (BSNRs) observed in the radio band is determined mainly either by a non-uniform interstellar medium (ISM) or by a non-uniform ambient magnetic field.

Context.Detailed hydrodynamic modeling explained several features of a fragment of the core of a Coronal Mass Ejection observed with SoHO/UVCS at 1.7 $R_{\odot}$on 12 December 1997, but some questions remained unsolved.

Context.In the framework of the study of the X-ray and optical emission in supernova remnants we focus on an isolated X-ray knot in the northern rim of the Vela SNR (Vela FilD), whose X-ray emission has been studied and discussed in Paper I.

Context.X-ray observations of evolved supernova remnants (e.g. the Cygnus loop and the Vela SNRs) reveal emission originating from the interaction of shock waves with small interstellar gas clouds.

We present the results of a five-day monitoring campaign with XMM-Newtonof six X-ray bright young stellar objects (YSOs) in the star-forming complex L1551 in Taurus. All stars present significant variability on the five-day time scale. Modulation of the light curve on time scales comparable with the star's rotational period appeared to be present in the case of one weak-lined T Tauri star. Significant spectral variations between the 2000 and the 2004 observations were detected in the (unresolved) classical T Tauri binary system XZ Tau: a hot plasma component which was present in the X-ray spectrum in 2000 had significantly weakened in 2004. As XZ Tau N was undergoing a strong optical outburst in 2000, which had terminated since then, we speculate on the possible relationship between episodic, burst accretion, and X-ray heating. The transition object HL Tau underwent a strong flare with a complex temperature evolution, which is indicative of an event confined within a very large magnetic structure (few stellar radii), similar to the ones found in YSOs in the Orion Nebula Cluster.

Aims.We analyze a well-defined loop system detected in a time-resolved observation in several spectral bands to characterize the structure and evolution of coronal loops. Methods.The dataset includes simultaneous sequences of images in the 171 Å, 195 Å and 284 Å filter bands of TRACE, and in one filter of Yohkoh/SXT, with a time coverage of about 2.5 h, and two rasters taken with SoHO/CDS in twelve relevant lines, forming between $\log T \approx 5.4$(O V 629 Å) and $\log T \approx 6.4$(Fe XVI 360 Å). The loop is initially best seen in the TRACE 195 Å filter band, with some correspondence to the simultaneous SXT images, and later in the 171 Å filter band, with good correspondence to the CDS raster images in the lines with formation temperature around $\log T \approx 6.0{-}6.1$. We have taken as pixel-by-pixel background the latest TRACE, Yohkoh and CDS images where the loop has faded out. We examine the loop morphology evolution, the light curves, the TRACE filter ratio distribution and evolution, the images and emission measure from the CDS spectral lines.Results.Our analysis detects that, after background subtraction, the emission along the loop and its evolution are non-uniform, especially in the 171 Å filter band, and that the TRACE 195/171 filter ratio has a moderately non-uniform distribution along the loop and evolves over time. Both the light curves and the filter ratio evolution indicate a globally cooling loop. Relatively hot plasma may be present at the beginning while, during the first CDS raster, the data indicate a rather moderate thermal structuring of the loop.Conclusions.Our analysis supports a coherent scenario across the different bands and instruments, points out difficulties in diagnostic methods and establishes quantitative basis for detailed forward modeling.

We model the hydrodynamic interaction of a shock wave of an evolved supernova remnant with a small interstellar gas cloud like the ones observed in the Cygnus loop and in the Vela SNR. We investigate the interplay between radiative cooling and thermal conduction during cloud evolution and their effect on the mass and energy exchange between the cloud and the surrounding medium. Through the study of two cases characterized by different Mach numbers of the primary shock (${\cal M}= 30$and 50, corresponding to a post-shock temperature $T\approx 1.7\times 10^6$K and ≈$ 4.7\times 10^6$K, respectively), we explore two very different physical regimes: for ${\cal M}= 30$, the radiative losses dominate the evolution of the shocked cloud which fragments into cold, dense, and compact filaments surrounded by a hot corona which is ablated by the thermal conduction; instead, for ${\cal M}= 50$, the thermal conduction dominates the evolution of the shocked cloud, which evaporates in a few dynamical time-scales. In both cases we find that the thermal conduction is very effective in suppressing the hydrodynamic instabilities that would develop at the cloud boundaries.

We study the X-ray variability of the young open cluster Blanco 1 observed with the EPIC camera on board the XMM-NewtonX-ray observatory. The time coverage of EPIC observations has allowed us to address short time scale (hours) variability, while the comparison with previous ROSAT observations has allowed us to investigate the variability on time scale of six years. On the time scale of hours, dM stars of the cluster are more variable than solar-mass stars. The main features of X-ray light curves in dM stars appear to be essentially flare-like events with a typical duration of the order of a few ks, while dF–dG stars show smooth variations. Two intense flares were observed in the ZS76cluster member. From the analysis of the light curves and of the time resolved X-ray spectroscopy we infer that they occurred in arcades, made of several similar coronal loops (~1010cm long), ignited at ~15 ks time delay. Minor heat pulses may occur in the first flare. The similarity of the two flares and of the flaring inferred structures may suggest that the flares are physically connected to each other. Amplitude variations on the time scale of 6 years are smaller by a factor 2, whereas a factor of 10 is observed on the Sun in the same band. This implies a smaller amplitude of any analog of the 11-yr cycle in these young active coronae.

We study the contribution of an active region and its core to the luminosity and the spectrum of the Sun in the X-ray band and to the relevant solar emission measure vs. temperature distribution, EM(T). We also study the relevant changes in the course of four solar rotations, and the solar rotational modulation due to this active region, the only one present at that time. 
To this end, we have used a large sample of full-disk Yohkoh/SXT observations taken between July and October 1996, covering most of the active region evolution. From the Yohkoh/SXT data we have synthesized the X-ray spectra of the whole solar corona, and the focal plane data as they would be collected with Rosat/PSPC, XMM-Newton/EPIC and Chandra/ACIS. This work is part of a project to study the Sun as an X-ray star, using the solar data as a guide and a template for stellar observations.
We found that the active region contributes significantly to the X-ray spectrum of the Sun mainly during the first month of its evolution. The rotational modulation due to the active region causes a significant variability of the average X-ray flux, with only moderate spectral variation, in the pass-bands of Rosat/PSPC, XMM-Newton/EPIC and Chandra/ACIS.
We investigated the characteristics of the X-ray variability due to the rotational modulation, to the solar cycle, and to flares together with the possible implications on stellar X-ray variability. We derived the diagram of X-ray surface flux vs. spectral hardness ratio in the Rosat/PSPC band; we studied the variability due to the solar cycle and to the rotational modulation and we found that both lead to the same correlation between Fpspcand HRpspcwith a very steep slope. The variability due to the evolution of flares again produces a correlation between Fpspcand HRpspcbut with a much flatter slope than in the other two cases. Analogous results have been found when analyzing data in the format of XMM-Newton/EPIC and Chandra/ACIS.

We report results from a comprehensive study of the nearby M dwarf Proxima Centauri with the XMM-Newtonsatellite, using simultaneously its X-ray detectors and the Optical Monitor with its Uband filter. We find strongly variable coronal X-ray emission, with flares ranging over a factor of 100 in peak flux. The low-level emission is found to be continuously variable on at least three time scales (a slow decay of several hours, modulation on a time scale of 1 hr, and weak flares with time scales of a few minutes). Several weak flares are characteristically preceded by an optical burst, compatible with predictions from standard solar flare models. We propose that the Uband bursts are proxies for the elusive stellar non-thermal hard X-ray bursts suggested from solar observations. In the course of the observation, a very large X-ray flare started and was observed essentially in its entirety. Its peak luminosity reached $3.9\times 10^{28}$erg s-1[0.15–10 keV], and the total X-ray energy released in the same band is derived to be $1.5\times 10^{32}$ergs. This flare has for the first time allowed to measure significant density variations across several phases of the flare from X-ray spectroscopy of the O viiHe-like triplet; we find peak densities reaching up to $4\times 10^{11}$cm-3for plasma of about 1–5 MK. Abundance ratios show little variability in time, with a tendency of elements with a high first ionization potential to be overabundant relative to solar photospheric values. Using Fe xviilines with different oscillator strengths, we do not find significant effects due to opacity during the flare, indicating that large opacity increases are not the rule even in extreme flares. We model the large flare in terms of an analytic 2-Ribbon flare model and find that the flaring loop system should have large characteristic sizes ($\approx $1$R_*$) within the framework of this simplistic model. These results are supported by full hydrodynamic simulations. Comparing the large flare to flares of similar size occurring much more frequently on more active stars, we propose that the X-ray properties of active stars are a consequence of superimposed flares such as the example analyzed in this paper. Since larger flares produce hotter plasma, such a model also explains why, during episodes of low-level emission, more active stars show hotter plasma than less active stars.

We model in detail a flare observed on Proxima Centauri with the EPIC-PN on board XMM-Newton at high statistics and high time resolution and coverage. Time-dependent hydrodynamic loop modeling is used to describe the rise and peak of the light curve, and a large fraction of the decay, including its change of slope and a secondary maximum, over more than 2 h. The light curve, the emission measure and the temperature derived from the data allow us to constrain the loop morphology and the heating function and to show that this flare can be described with two components: a major one triggered by an intense heat pulse injected in a single flaring loop with half-length ≈$1.0 \times 10^{10}$cm, the other one by less intense heat pulses released about 1/2 h after the first one in related loop systems, probably arcades, with the same half-length. The heat functions of the two loop systems appear very similar: an intense pulse located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The latter result and the similarity to at least one solar event (the Bastille Day flare in 2000) indicate that this pattern may be common to solar and stellar flares.

We report the XMM-Newtonobservation of a large X-ray flare from the Herbig Ae star V892 Tau. The apparent low mass companion of V892 Tau, V892 Tau NE, is unresolved by XMM-Newton. Nevertheless there is compelling evidence from combined XMM-Newtonand Chandradata that the origin of the flare is the Herbig Ae star V892 Tau. During the flare the X-ray luminosity of V892 Tau increases by a factor of ${\sim} 15$, while the temperature of the plasma increases from $kT \simeq 1.5$keV to $kT \simeq 8$keV. From the scaling of the flare event, based on hydrodynamic modeling, we conclude that a 500 G magnetic field is needed in order to confine the plasma. Under the assumptions that a dynamo mechanism is required to generate such a confining magnetic field and that surface convection is a necessary ingredient for a dynamo, our findings provide indirect evidence for the existence of a significant convection zone in the stellar envelope of Herbig Ae stars.

We analyze a space-, time- and spectral-resolved SoHO/CDS observation of the evolution of an active region over a time lapse of approximately three hours in various spectral lines emitted in the interval of temperature $1.3 \times 10^4 < T < 2.5 \times 10^6$K. We identify and characterize two structures of interest: a longer coronal loop (${\approx} 5.5\times10^9$cm), relatively steady and well visible in lines forming at coronal temperatures (e.g. Fe XIV 334.17 Å, Fe XVI 360.76 Å) and a smaller one (${\approx} 1.8\,\times\,10^9$cm), transient and visible only in cooler lines (O IV 554.51 Å, O V 629.73 Å). In the hot lines, the longer loop has a bright apex and an emission distribution of constant shape, but of moderately variable absolute intensity; the region around the loop apex shows a distinct brightening practically in all lines. In the hot lines, the brightening appears as a minor perturbation over a steadily high emission level. In the same region the emission measure vs temperature of the hottest lines indicates a temperature of ∼2 MK, lower than the temperature obtained from Yohkoh data taken just before the CDS observation. Comparison with steady-state loop scaling laws and with plasma time scales, and connection to cooling or heating episodes are discussed. As for the cool loop, its whole evolution, from ignition to disappearance, is directly observed, confirming the highly transient nature of such structures. The O V line is blue-shifted at one footpoint, indicating an upflow associated with the loop ignition.

Long-lasting, intense, stellar X–ray flares may approach conditions of breaking magnetic confinement and evolving in open space. In the perspective of searching for possible tracers of non-confinement, we explore this hypothesis with hydrodynamic simulations of flares occurring in a non-confined corona: model flares are triggered by a transient impulsive heating injected in a plane-parallel stratified corona. The plasma evolution is described by means of a numerical 2-D model in cylindrical geometry $R,Z$. We explore the space of fundamental parameters. As a reference model, we consider a flare triggered by a heating pulse of 10 erg cm-3s-1lasting 150 s and released in a region ~ 109cm wide and at a height ~$ 2 \times 10^9$cm from the base of the stellar surface. The pressure at the base of the corona of the unperturbed atmosphere is 0.1 dyne cm-2. The heating would cause a 20 MK flare if delivered in a 40 000 km long closed loop. The modeled plasma evolution in the heating phase involves the propagation of a 10 MK conduction front and the evaporation of a shocked bow density front upwards from the chromosphere. As the heating is switched off, the temperature drops in few seconds while the density front still propagates, expanding, and gradually weakening. This kind of evolution is shared by other simulations with different coronal initial pressure, and location, duration and intensity of the heating. The X-ray emission, spectra and light curves at the ASCA/SIS focal plan, and in two intense X–ray lines (Mg XI at 9.169 Å and Fe XXI at 128.752 Å), have been synthesized from the models. The results are discussed and compared to features of confined events, and scaling laws are derived. The light curves invariably show a very rapid rise, a constant phase as long as the constant heating is on, and then a very fast decay, on time scales of few seconds, followed by a more gradual one (few minutes). We show that this evolution of the emission, and especially the fast decay, together with other potentially observable effects, are intrinsic to the assumption of non–confinement. Their lack indicates that observed long–lasting stellar X–ray flares should involve plasma strongly confined by magnetic fields.

We revisit a well-studied solar flare whose X-ray emission originating from a simple loop structure was observed by most of the instruments on board SMM on November 12, 1980. The X-ray emission of this flare, as observed with the XRP, was successfully modeled previously. Here we include a detailed modeling of the transition region and we compare the hydrodynamic results with the UVSP observations in two EUV lines, measured in areas smaller than the XRP rasters, covering only some portions of the flaring loop (the top and the foot-points). The single loop hydrodynamic model, which fits well the evolution of coronal lines (those observed with the XRP and the Fe xxi1354.1 Å line observed with the UVSP) fails to model the flux level and evolution of the O v1371.3 Å line.

Using a hydrodynamic model we have re-analyzed large flaring events on three different categories of pre-main sequence (PMS) stars: the young stellar object (YSO) YLW 15, the classical T Tauri star (CTTS) LkHα92, the weak-line T Tauri star (WTTS) V773 Tau, and the WTTS HD 283572 (the first three objects were observed by ASCA, the last by ROSAT; all observations have been previously reported in the literature). The first three flares were previously analyzed on the basis of a quasi-static model mostly used up to now, consistently yielding large loops ($L \ga R_*$) and no evidence of sustained heating. Our hydrodynamic modeling approach, however, shows that the size of the flaring regions must be much smaller ($L \la R_*$) and moreover this method shows in all cases evidence of vigorous sustained heating during the flare decay, so that the decay of the observed light curve actually reflects the temporal profile of the heating rather than that of the free decay of the heated loop(s). The events on the protostar YLW 15 have durations comparable to the stellar rotation period, so that their limited size and their lack of self-eclipses give evidence of a polar location on the star. This is in contrast with the recently advanced hypothesis that these flares are due to long loops spanning the region between the star and the accretion disk. In general, the present analysis shows that flaring coronae on PMS stars have a structure similar to the coronae on older active stars.

Context. High spectral resolution X-ray observations of classical T?Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T?2-3? 106?K and density ne?1011-1013?cm-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreting material, but do not allow us to analyze the stability of the material and its position in the stellar atmosphere.Aims. We investigate the dynamics and stability of shock-heated accreting material in classical T?Tauri stars and the role of the stellar chromosphere in determining the position and thickness of the shocked region.Methods. We perform one-dimensional hydrodynamic simulations of the impact of an accretion flow on the chromosphere of a CTTS, including the effects of gravity, radiative losses from optically thin plasma, thermal conduction and a well tested detailed model of the stellar chromosphere. We present the results of a simulation based on the parameters of the CTTS MP?Mus.Results. We find that the accretion shock generates an hot slab of material above the chromosphere with a maximum thickness of?1.8 ?109?cm, density ne?1011-1012?cm-3, temperature T?3?106?K, and uniform pressure equal to the ram pressure of the accretion flow (~450?dyn?cm-2). The base of the shocked region penetrates the chromosphere and remains at a position at which the ram pressure is equal to the thermal pressure. The system evolves with quasi-periodic instabilities of the material in the slab leading to cyclic disappearance and re-formation of the slab. For an accretion rate of ~10-10?M??yr-1, the shocked region emits a time-averaged X-ray luminosity of LX?7? 1029?erg?s-1, which is comparable with the X-ray luminosity observed in CTTSs of identical mass. Furthermore, the X-ray spectrum synthesized from the simulation reproduces in detail all the main features of the Oviii and Ovii?lines of the star MP?Mus.

In order to test the hypothesis that a greater sympathetic activity underlies partial reversibility of the bronchial obstruction in selected patients with chronic obstructive pulmonary disease (COPD), we assessed the pulmonary clearance of inhaled 123I-meta-iodobenzylguanidine (123I-MIBG) radioaerosol in 10 patients with fixed and nine with reversible obstruction. The clearance of inhaled 123I-MIBG is known to be inversely related to 123I-MIBG uptake by adrenergic terminals. Groups were matched for age and judged free from confounding comorbidity. The penetration index did not distinguish between the groups (fixed obstruction, 97.39±14.59; reversible obstruction, 89.09±19.95; P0.659); this excludes the possibility that the inequality of tracer penetration could affect 123I-MIBG clearance. The 123I-MIBG clearance was 140.92±7.67 min in patients with fixed obstruction and 151.08±31.54 min in patients with reversible obstruction (P0.604). In conclusion, COPD patients with fixed and reversible obstruction show comparable binding of the tracer to adrenergic pulmonary receptors. Thus, a greater receptor responsiveness or post-receptor mechanism probably underlies the partial reversibility of bronchial obstruction.

Introduction: Surgical release is the most effective therapy for the symptoms of carpal tunnel syndrome (CTS). It is widely considered that surgery may be ineffective in ‘extreme’ cases (those with atrophy of the thenar eminence muscles and no sensory and motor response of the median nerve).

A prospective study of electrophysiological examination and the Boston self-administered questionnaire (BQ) was carried out in patients with surgically-treated carpal tunnel syndrome. There were 104 hands in 93 patients (13 men and 80 women, mean age 56 years). The BQ was used to assess the severity of symptoms and function, and nerve conduction studies were done before surgical release by short incision at the palm, and at follow-ups 1 and 6 months after surgery. The BQ severity score improved or became normal in 98% of hands. The mean BQ scores and distal sensory and motor conduction velocities in the median nerve showed significant improvement at the 1 month follow-up. Further significant improvement was found at 6 months. There was no relationship between the improvements in BQ scores and the distal conduction in the median nerve. The degree of improvement in sensory and motor distal conduction velocities could be forecast from presurgical values, whereas the degree of improvement in the symptoms and the functional status after release could not be predicted from the presurgical BQ scores.

Viene riferito un caso di malattia di von Hippel-Lindau con emangioblastomi multipli (cerebellari, bulbare, spinale) senza interessamento retinico o viscerale. Ripetuti controlli TC ed RM nell'arco di sei mesi hanno permesso di seguire l'evoluzione delle lesioni, di cui una cerebellare operata. Di particolare rilevanza è apparsa la trasformazione di una lesione nodulare in cistica con un rapido accrescimento della cisti e l'apparire di una nuova lesione. Viene sottolineata la netta superiorità della risonanza magnetica nucleare con Gadolinio per una più precisa valutazione delle lesioni di questa malattia.

The long-term results of surgical treatment of 102 patients for cervical myeloradiculopathy due to spondylosis or disc hernia are reported and discussed. The result was excellent or good in 63% of cases and progression of the disease was arrested in over 90%. Statistical analysis of the preoperative clinical data shows that length of history, neurological status and age significantly affect the outcome. The pre- and post-operative symptoms are analysed and the complications reported. On the evidence of the results reported surgery is successful in a high percentage of case and carries few risks. It can even be recommended in doubtful cases, often elderly patients, when it is difficult to gauge how far a myelopathy is spondylotic and to what extent due to other causes.

Summary We present the results of a study comparing two groups of patients who underwent neurosurgical operations, one pretreated with Ampicillin (184) and the other not (193), in comparable timespans. The results of this study argue for a beneficial action of Ampicillin prophylaxis on neurosurgical infections. A brief discussion of the appropriate literature is given.

Summary The operative results in 37 consecutive patients suffering from developmental stenosis of the lumbar spinal canal, compared with those in spondylosis and disc herniations, are discussed. The diagnostic certainty of stenosis, suspected on the bases of clinical and radiographic data, is reached only at the operating table. To judge the usefulness of the operation we have considered not only the patients' verdicts, but also the improvements in neurological signs and the appearance of new deficits. Satisfactory results are around 80%, slightly less good with stenosis than with the other causes of lumbar syndrome. Radiographic study with contrast medium is mandatory. Dimer-X has been used with very clear radiographic findings and very few complications. Operating technique is also described: a wide laminectomy with facetectomy is advised. The great importance of early physiotherapy is emphasized.

A case of ossification of the posterior longitudinal ligament, documented by spinal X-ray, myelography and CT scanning of the spinal cord is reported. The patient underwent decompressive laminectomy by posterior approach, which was successful. The case is discussed in the light of recent published data.

We report the case of a 41 year old man who complained of a severe bilateral deficit of the anterior tibial compartment two hours after prolonged exercise. On admission there was no spontaneous or evoked pain, no objective sensory deficit but total loss of dorsiflexion of feet and toes. Electrophysiological investigation showed no voluntary or evoked electrical activity in tibial and extensor digitorum muscles; while peroneus longus and gastrocnemius muscles showed a nearnormal pattern. On the other hand a weak motor response was obtained by direct stimulation of the anterior tibial muscle belly. An early bilateral fasciotomy was followed by almost complete recovery of the spontaneous and evoked motor activities of the tibial anterior muscles. On the basis of these findings we discuss the possible pathogenetic role of a neuroapraxic block of the deep peroneal nerve where it crosses the anterior fibular septum and supply a possible interpretation of the absence of pain.

We report findings concerning energy transport and dynamics in flares during the impulsive and gradual phases based on new ground-based and space observations (notably fromYohkoh). A preheating sometimes occurs during the impulsive phase. Caxix line shifts are confirmed to be good tracers of bulk plasma motions, although strong blue shifts are not as frequent as previously claimed. They often appear correlated with hard X-rays but, forsome events, the concept that electron beams provide the whole energy input to the thermal component seems not to apply. Theory now yields: new diagnostics of low-energy proton and electron beams; accurate hydrodynamical modeling of pulse beam heating of the atmosphere; possible diagnostics of microflares (based on X-ray line ratio or on loop variability); and simulated images of chromospheric evaporation fronts. For the gradual phase, the continual reorganization of magnetic field lines over active regions determines where and when magnetic reconnection, the mechanism favoured for energy release, will occur. Spatial and temporal fragmentation of the energy release, observed at different wavelengths, is considered to be a factor as well in energy transport and plasma dynamics.

ASAP (Analysis System for Astrophysical Plasmas), developed at the Osservatorio Astronomico di Palermo, is a package of procedures based on IDL. It is aimed at the detailed presentation of theoretical models of astrophysical plasmas and the accurate comparison with observational data, up to fittings of specific observations. It is also useful for the prediction of specific observations, and for the simulation of the expected performances of forthcoming instruments, for instance those on board SOHO.

We present a two-dimensional hydrodynamic code suited to study astrophysical flows in many different environments. The code solves the hydrodynamic equations in conservative form in the most used coordinate systems and is based on an explicitfully two-dimensionalflux corrected transport (FCT) technique, which ensures an accurate description of steep gradient regions and shocks, a relatively ample flexibility to include a variety of physical effects, and a good efficiency for speed on vector or array processors. Extensive testing has allowed an accurate «tuning» of the FCT numerical parameters. This code is among the best FCT codes and performs well in a whole set of demanding strongly nonlinear hydrodynamic tests, getting close to performances of more complex codes, while remaining less computationally expensive and more than sufficient for most astrophysical applications.

Context.High resolution X-ray spectroscopy has revealed soft X-rays from high density plasma in classical T Tauri stars (CTTSs), probably arising from the accretion shock region. However, the mass accretion rates derived from the X-ray observations are consistently lower than those derived from UV/optical/NIR studies.

Context.Inverse problems are of great importance in astrophysics, e.g., for deriving information about the physical characteristics of hot optically thin plasma sources from their extreme ultraviolet and X-ray spectra.

Context.High resolution X-ray observations of classical T Tauri stars (CTTSs) show a soft X-ray excess due to high density plasma (ne= 1011−1013cm-3). This emission has been attributed to shock-heated accreting material impacting onto the stellar surface.

Context. Flares are dynamic events which involve rapid changes in coronal magnetic topology end energy release. Even if they may be localized phenomena, the magnetic disturbance at their origin may propagate and be effective in a larger part of the active region.Aims. We investigate the temporal evolution of a flaring active region with respect to the loops morphology, the temperature, and emission measure distributions.Methods. We consider Hinode/XRTdata of a the 2006 November 12th C1.1 flare. We inspect the evolution of the morphology of the flaring region also with the aid of TRACE data. XRT filter ratios are used to derive temperature and emission measure maps and evolution. Results. The analyzed flare includes several brightenings. We identify a coherent sequence of tangled and relaxed loop structures before, during, and after the brightenings. Although the thermal information is incomplete because of pixel saturation at the flare peak, thermal maps show fine, evolving spatial structuring. Temperature and emission measure variations show up in great detail, and we are able to detect a secondary heating of larger loops close to the proper flaring region. Finally we estimate the amount of energy released in these flaring loops during the flare decay.

Context. Flares are dynamic events which involve rapid changes in coronal magnetic topology end energy release. Even if they may be localized phenomena, the magnetic disturbance at their origin may propagate and be effective in a larger part of the active region.

Aims. Using TRACE coronal observations, we compare the analysis and diagnostics of coronal loop after subtracting the background with two different and independent methods.Methods. We analyze sequences of images in the 171 Å and 195 Å  filter bands of TRACE. One background subtraction method consists of considering background values obtained by interpolating between concentric strips around the analyzed loop. Another involves a pixel-to-pixel subtraction of the final image after the loop has completely faded out, used by Reale and Ciaravella.Results. We compare the emission distributions along the loop obtained with the two methods and find that they differ considerably. We also find differences in the related filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. After applying the other type of subtraction, the diagnostics are much less clear.Conclusions. The background subtraction should be treated with care when analyzing a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction by means of interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and the large amount of subtracted emission in TRACE observations.

Aims. Using TRACE coronal observations, we compare the analysis and diagnostics of coronal loop after subtracting the background with two different and independent methods.

Context. X-ray emitting features originating from the interaction of supernova shock waves with small interstellar gas clouds are revealed in many X-ray observations of evolved supernova remnants (e.g., Cygnus Loop and Vela), but their interpretation is not straightforward.Aims. We develop a self-consistent method for the analysis and interpretation of shock-cloud interactions in middle-aged supernova remnants, which can provide the key parameters of the system and the role of relevant physical effects such as thermal conduction, without the need to perform ad-hoc numerical simulations and bother about morphology details.Methods. We explore all the possible values of the shock speed and cloud density contrast relevant to middle-aged SNRs with a set of hydrodynamic simulations of shock-cloud interaction including the effects of thermal conduction and radiative cooling. From the simulations, we synthesize spatially and spectrally resolved focal-plane data as they would be collected with XMM-Newton/EPIC, an X-ray instrument commonly used in these studies.Results. We develop and calibrate two diagnostic tools, the first based on the mean photon energy versus count-rate scatter plot and the second on the spectral analysis of the interaction region, that can be used to highlight the effects of thermal conduction and to derive the shock speed in case of efficient conduction at work. These tools can be used to ascertain information from X-ray observations, without the need to develop detailed and ad-hoc numerical models for the interpretation of the data.