Shear transformation distribution and activation in glasses at the atomic scale.

We characterize shear transformations (STs) at the atomic scale in a model of amorphous silicon using a mapping on Eshelby inclusions. We investigate the effect of pressure, glass relaxation, as well as damage on the ST characteristics. We show that the characteristic ST effective volume, γ_{0}V_{0}, product of the ST plastic shear strain γ_{0} and volume V_{0}, does not depend significantly on an applied pressure but increases with accumulated plastic deformation from about 10Å^{3} in the pseudoelastic regime to about 60Å^{3} once plastic flow sets in. Furthermore, by using nudged elastic band calculations, we measure the energy barrier against ST activation. Analyzing different paths leading to either an isolated ST or an avalanche, we show that the barrier is systematically controlled by the first ST with an activation volume equal to the effective volume of the ST at the activated state, which represents only a fraction of the complete ST volume. The activation volume is also found smaller for avalanches, presumably because of accumulated local damage. This work provides essential information to build reliable mesoscale models of plasticity.

Mapping between atomistic simulations and Eshelby inclusions in the shear deformation of an amorphous silicon model.

In this paper we perform quasistatic shear simulations of model amorphous silicon bulk samples with Stillinger-Weber-type potentials. Local plastic rearrangements identified based on local energy variations are fitted through their displacement fields on collections of Eshelby spherical inclusions, allowing determination of their transformation strain tensors. The latter are then used to quantitatively reproduce atomistic stress-strain curves, in terms of both shear and pressure components. We demonstrate that our methodology is able to capture the plastic behavior predicted by different Stillinger-Weber potentials, in particular, their different shear tension coupling. These calculations justify the decomposition of plasticity into shear transformations used so far in mesoscale models and provide atomic-scale parameters that can be used to limit the empiricism needed in such models up to now.

Assessing the composition of hetero-epitaxial islands via morphological analysis: an analytical model matching GeSi/Si(001) data.

A simple, but still three-dimensional, model describing the morphological stability of realistic SiGe islands on Si(001) is presented. The experimental evolution toward steeper islands with volume can be predicted for any average composition. Despite the use of elastic theory for stress relaxation under the assumption of a uniform SiGe distribution, and of a common mean surface energy of the faceted islands, the model seems to capture the essence of the energetic balance determining the morphological evolution with volume, with no fitting parameters. This is suggested by close comparison with molecular beam epitaxy data at three different temperatures (i.e. compositions). The good agreement also allows for interpreting the minor scattering of experimental data with temperature and provides a reliable tool for extracting the average Ge content from standard atomic force microscopy analysis.

[Spiral computerized tomography in the diagnosis of acute occlusion of the abdominal aorta. A case report]. / La Tomografia Computerizzata spirale nella diagnosi dell'occlusione acuta dell'aorta addominale. Descrizione di un caso.

Aim of this report is to present a case of acute occlusion of the abdominal aorta recognized by spiral-CT. After a brief description of the etiology and pathology of abdominal aorta acute occlusion, stress is laid on diagnostic role of spiral-CT, based on personal and literature data. The advantage of spiral respect to non-spiral CT is the quicker examination time which is very important, mostly in emergencies. On the contrary, the diagnosis of acute abdominal aorta occlusion is not modified by volumetric CT respect to non-spiral and it is based on the absence of aorta contrast enhancement above the occlusion level.

[Computerized tomography of the lungs in patients with congenital immunodeficiency. Comparison with clinicoradiologic assessment]. / Valutazione con Tomografia Computerizzata del polmone dei pazienti con immunodeficienze congenite. Confronto con la valutazione clinico radiologica.

PURPOSE: Primary immunodeficiencies (PI) are a heterogeneous and relatively uncommon group of conditions. As a result of one or more immune system abnormalities, PI decrease the body resistance to infections. The respiratory tract is affected in most cases as a result of its natural exposure to pathogenic agents; repeated infections can lead to pulmonary alterations. We investigated the yield of High Resolution CT (HRCT) and Helical CT in pediatric patients with different PI and then correlated the CT patterns with the patients' clinical history and physical status. MATERIAL AND METHODS: We examined 19 pediatric patients with different types of PI. All patients presented recurrent infections (rhinosinusitis, bronchitis, bronchopneumonia) with cough and chronic catarrh for at least 3 months a year. Fifteen patients were examined with HRCT and 4 with Helical CT. Images were evaluated for presence and severity of alveolitis, bronchiectasis, peribronchial thickening, mucous plugs, air trapping, bronchiolitis, consolidation, abscesses, bullae, emphysema and fibrotic changes. All parameters were given a score and a partial and an overall score calculated for each parameter. All scores were compared to study the correlations between CT patterns, clinical history and patients' status and for possible characterization of the different groups by CT patterns. Finally, all alterations were classified by their anatomical distribution in each pulmonary lobe. RESULTS: Scores ranged 0 to 18, with a mean of 8.1 points. There were no correlations between CT patterns, patients' history and clinical status and any disease type. The midlobe was the preferential site for bronchiectasis while lower lobes were more involved by other conditions, such as consolidation, air trapping and alveolitis. CONCLUSIONS: Both HRCT and Helical CT proved to be useful tools for monitoring PI patients. The two techniques can be especially valuable in symptomatic patients with negative radiographic findings because they can show (non-)reversible damage, which helps improve planning of drug and/or physical therapy. The scoring system, even if not closely correlated with clinical signs, could be a major tool for PI follow-up and for monitoring treatment success.

Blunt trauma of the spleen: the delayed rupture in computed tomography.

We retrospectively reviewed CT scans of 18 patients (12 males and 6 females; mean age: 43.6 years) with the diagnosis of blunt splenic trauma. All patients underwent CT at different times after the trauma. The cases were divided into 2 groups: according to the time at which the CT was performed, the 1st group consisted of 11 patients scanned within 48 h after the trauma; the 2nd group consisted of 7 patients studied with CT at variable times after the traumatic event (mean time: 6.5 days; range 3-13 days). All lesions in the 1st group (11 patients) had indistinct margins, while lesions of patients in the 2nd group (7 patients) always showed clean-cut and regular edges. Early lesions were always hyperdense, late ones hypodense. CT diagnosis always matched the surgeon's diagnosis. We can confirm the diagnostic value of CT of splenic lesions in blunt abdominal traumas.

[An analysis of a case series of 342 short-stature patients examined by the Tanner-Whitehouse 2 (TW2) method]. / Analisi della casistica di 342 pazienti con bassa statura esaminati con il metodo Tanner-Whitehouse 2 (TW2).

342 short-stature patients were examined to assess the agreement between anagraphic and bone ages. 190 men and 152 women (age range: 0 to 17.5 years) underwent conventional radiographs of the left wrist. The radiographs were studied with the TW2 method which provides an index of the skeletal maturity of short and long bones and a global index of the hand. The bone ages thus obtained were compared with anagraphic ages. Patients' statures were compared with their parents' ones. Finally, radiation exposures were evaluated. Anagraphic and bone ages were in agreement in 199 patients and in disagreement in 220. Three patients were adult. The short stature in 78 patients was in agreement with their parents' one, while 253 patients had at least one parent with normal stature. No comparison could be made in 11 patients. In conclusion, TW2 is a simple method to calculate bone age (in months and years) and to select the patients to submit to further examinations and to hormone therapy.

[Critical review of the diagnostic protocol in patients with head injury]. / Revisione critica del protocollo diagnostico nei pazienti con trauma cranico.

The results of a retrospective review of the conventional radiographs performed on head injury patients are reported. Skull radiography findings were compared with clinical symptoms and CT results, when CT was performed, to investigate the presence of intracranial lesions. The radiographs of 2,285 adult patients of both sexes were evaluated: skull fractures were observed in 21/2,285 patients (0.9%) only. CT was positive for an intracranial lesion in 18 of 21 patients (85.71%). Clinical symptoms were divided into three groups according to lesion severity and to neurologic impairment. 979 patients were asymptomatic and 1,306 were symptomatic: 1,114 patients were included in group I, their symptoms being nausea, vomit and loss of consciousness for less than ten minutes, 124 were included in group II (epistaxis and loss of consciousness for more than 10 minutes) and 68 were included in group III (coma and focal neurologic signs). All the patients in groups II and III and 30 patients in group I were submitted to CT--222 CT exams on the whole. Thirty-five patients in group III and 9 in group II had an intracranial lesion on CT, while CT findings were normal in all group-I patients. Thus, we conclude that the presence of a skull fracture is not always correlated with the presence of intracranial lesions. The latter are more likely to be correlated with clinical symptoms, especially coma and neurologic impairement. Therefore, the higher value is confirmed of the clinical examination than of conventional radiographs in head injury patients.

[Role of computed tomography in splenic blunt trauma]. / Il ruolo della Tomografia Computerizzata nei traumi chiusi della milza.

The CT scans of 18 patients (12 males and 6 females; mean age: 43.6 years) with splenic blunt trauma were reviewed. CT examinations had been made at different times after trauma. The CT images were grouped according to the time of examination and both structure and densitometry were evaluated in all lesions. In all cases CT findings were correlated with surgical and pathologic data. The patients were divided into two groups: group I included 11 subjects in whom CT had been performed within 48 hours following trauma and group II included 7 patients who had undergone CT at different times after trauma (3-13 days; mean: 6.5 days). All the lesions in group I exhibited blurred outlines, while the lesions in group II had clear-cut margins. The lesions in group I were always hyperdense while those in group II were hypodense. CT diagnosis was always in agreement with surgical findings. In conclusion, we confirm the value of CT in the examination of splenic lesions by blunt abdominal trauma. The evolution of splenic lesions is usually typical: CT yields useful information for injury evaluation and is therefore very important to plan treatment. We believe that CT should be performed as soon as possible, even on the basis of minor clinical and laboratory data.

[Computerized tomography and conventional radiography in the diagnosis of destructive spondyloarthropathy. Our experience with 30 patients undergoing periodic hemodialysis]. / Tomografia computerizzata e radiografia tradizionale nella diagnosi della spondiloartropatia destruente. Nostra esperienza in 30 pazienti sottoposti a emodialisi periodica.

Thirty patients of both sexes (15 males and 15 females) with chronic renal failure who had under gone hemodialysis for 2-184 months (mean 45.1 months) were examined with conventional radiographs of the cervical spine and thin-layer CT of C4-C5-C6 to evaluate the radiographic patterns of destructive spondyloarthropathy. The radiographic patterns obtained with conventional and CT exams were compared with one another and with clinical (carpal tunnel syndrome) and biochemical data (alkaline phosphatase, parathormon, Ca, P, Ca/P, Al, beta 2-microglobulin). DSA (erosion and narrowing of the intervertebral space, collapse of the vertebral body and erosion of the vertebral plates) was recognized in 7 patients with conventional radiographs and in 11 patients with CT thanks to greater CT capabilities to recognize minimal osteolytic lesions of the vertebral body. All the patients with destructive spondyloarthropathy had personal and hemodialysis age higher than those without destructive spondyloarthropathy: 59.3 vs 57.7 years; 49 vs 39 months. Parathormon and alkaline phosphatase were increased while beta 2-microglobulin was normal. Only 2 patients with DSA had carpal tunnel syndrome. In conclusion, CT is a valuable technique for the diagnosis of destructive spondyloarthropathy but it must be performed only after conventional radiographs of the cervical spine or in the presence of clinical signs of destructive spondyloarthropathy (parathormon and beta 2-microglobulin increased, long-term hemodialysis).

[Percutaneous transluminal laser angioplasty. Initial clinical experience in 9 patients]. / L'angioplastica percutanea transluminale con laser. Iniziale esperienza clinica in 9 pazienti.

In this paper the authors report on a new technique--percutaneous transluminal laser angioplasty (PLR) which was performed on 9 patients with iliac and/or femoro-popliteal artery occlusion. All patients were males (mean age: 64.5 years) and had arterial occlusion (mean length: cm 12.5). PLR was performed with an argon laser (max power: 16 Watts). In 8 out of 9 patients (88.8%) a complete recanalization was obtained of the occluded arterial tract, without complications. In one case only (12.2%) there was an arterial wall perforation with unsatisfactory results. In our opinion, PLR has proven a simple methodology, which can be performed on any patient due to the very low incidence of severe complications and distal embolism. Moreover, PLR has quite low costs, and does not prevent eventual surgical/percutaneous interventions.

Cholangiographically-enhanced CT of the pancreas and biliary tree.

Cholangiographically-enhanced CT scans were performed on nine patients with biliary obstruction or suspected pancreatic masses. The opacification of the biliary tree was obtained by slow infusion of 25 ml of cholangiographic contrast medium diluted in 75 ml of saline and administered 45 mins before the CT examination. Two separate CT sequences were obtained, one with cholangiographic contrast alone, the other with associated parenchymal enhancement. The tolerability of the overall procedure was very good. The measurement of the HU values of the biliary ducts showed a marked increase in bile density. These structures could easily be appreciated within the liver and in the porta hepatis; the pancreatic head and its relationships with the main bile duct were evident. The densitometric measurement of the liver parenchyma before and after contrast enhancement did not show any variation with respect to the standard HU values. Cholangiographically-enhanced CT proved to be useful for the diagnosis of biliary obstruction; it may also be a promising diagnostic tool for the evaluation of pancreatic masses.