Semi-quantum approach for fast atom diffraction: solving the rainbow divergence

In this work we introduce a distorted wave method, based on the Initial Value Representation (IVR) approach of the quantum evolution operator, in order to improve the semiclassical description of rainbow effects in diffraction patterns produced by grazing scattering of fast atoms from crystal surfaces. The proposed theory, named Surface Initial Value Representation (SIVR) approximation, is applied to He atoms colliding with a LiF(001) surface along low indexed crystallographic channels. For this collision system the SIVR approach provides a very good representation of the quantum interference structures of experimental projectile distributions, even in the angular region around classical rainbow angles where common semiclassical methods diverge.Comment: 8 pages, 5 figure

Influence of the lighting on Fast Atom Diffraction studied via a semi-quantum approach

The influence of the collimating conditions of the incident beam on diffraction patterns produced by grazing scattering of fast atoms off crystal surfaces is studied within a semi-quantum approach, named Surface Initial Value Representation (SIVR) approximation. In this approach we incorporate a realistic description of the incident particle in terms of the collimating parameters, which determine the surface area that is coherently illuminated. The model is applied to He atoms colliding with a LiF(001) surface after passing through a rectangular aperture. As it was experimentally observed [1], SIVR spectra as a function of the azimuthal angle are very sensitive to the width of the collimating slit. We also found that the length of the collimating aperture affects polar angle distributions, introducing additional interference structures for the longer collimating slits

Single- and double-slit collimating effects on fast-atom diffraction spectra

Diffraction patterns produced by fast He atoms grazingly impinging on a LiF(001) surface are investigated focusing on the influence of the beam collimation. Single- and double- slit collimating devices situated in front of the beam source are considered. To describe the scattering process we use the Surface Initial Value Representation (SIVR) approximation, which is a semi-quantum approach that incorporates a realistic description of the initial wave packet in terms of the collimating parameters. Our initial wave-packet model is based on the Van Cittert-Zernike theorem. For a single-slit collimation the width of the collimating aperture controls the shape of the azimuthal angle distribution, making different interference mechanisms visible, while the length of the slit affects the polar angle distribution. Additionally, we found that by means of a double-slit collimation it might be possible to obtain a wide polar angle distribution, which is associated with a large spread of the initial momentum perpendicular to the surface, derived from the uncertainty principle. It might be used as a simple way to probe the surface potential for different normal distances

Atomic ionization by multicharged ions interpreted in terms of poles in the velocity complex space

We study the single ionization of hydrogen and helium by the impact of a highly-charged Coulomb projectile. To interpretate the cross section we introduce a diagonal Pad\'{e} approximant. We find that the use of Pad\'{e}% [4,4] describes very well the Continnum Distorted Wave Eikonal Initial State theory within its range of validity. The nodes of the denominator of the Pad% \'{e} approximant give rise to four poles in the velocity complex plane: two in the upper plane and their conjugate in the lower plane. The dependence of these poles with the projectile charge can be reasonably fitted to give a closed-form for the ionization cross section, resulting a scaling very near to the one of Janev and Presnyakov. The experiments available were described very well in its entire velocity range with the use of a Pad\'{e}[8,8], having four poles in the upper plane and their conjugate in the lower plane. We conclude that the poles of the Pad\'{e} approximant seem to have all the information of the total ionization cross sectionComment: 18 pages, 4 figures and 3 table

Guideline on management of the acute asthma attack in children by Italian Society of Pediatrics.

BACKGROUND: Acute asthma attack is a frequent condition in children. It is one of the most common reasons for emergency department (ED) visit and hospitalization. Appropriate care is fundamental, considering both the high prevalence of asthma in children, and its life-threatening risks. Italian Society of Pediatrics recently issued a guideline on the management of acute asthma attack in children over age 2, in ambulatory and emergency department settings. METHODS: The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology was adopted. A literature search was performed using the Cochrane Library and Medline/PubMed databases, retrieving studies in English or Italian and including children over age 2 year. RESULTS: Inhaled ß2 agonists are the first line drugs for acute asthma attack in children. Ipratropium bromide should be added in moderate/severe attacks. Early use of systemic steroids is associated with reduced risk of ED visits and hospitalization. High doses of inhaled steroids should not replace systemic steroids. Aminophylline use should be avoided in mild/moderate attacks. Weak evidence supports its use in life-threatening attacks. Epinephrine should not be used in the treatment of acute asthma for its lower cost / benefit ratio, compared to β2 agonists. Intravenous magnesium solphate could be used in children with severe attacks and/or forced expiratory volume1 (FEV1) lower than 60% predicted, unresponsive to initial inhaled therapy. Heliox could be administered in life-threatening attacks. Leukotriene receptor antagonists are not recommended. CONCLUSIONS: This Guideline is expected to be a useful resource in managing acute asthma attacks in children over age 2

Africa and the Americas in the Columbian Exchange: an Interview with Judith Carney

Africa and the Americas in the Columbian Exchange: an Interview with Judith CarneyAfrica and the Americas in the Columbian Exchange: an Interview with Judith CarneyAfrica and the Americas in the Columbian Exchange: an Interview with Judith Carne

Ocular manifestations in Gorlin-Goltz syndrome

Background: Gorlin-Goltz syndrome, also known as nevoid basal cell carcinoma syndrome, is a rare genetic disorder that is transmitted in an autosomal dominant manner with complete penetrance and variable expressivity. It is caused in 85% of the cases with a known etiology by pathogenic variants in the PTCH1 gene, and is characterized by a wide range of developmental abnormalities and a predisposition to multiple neoplasms. The manifestations are multiple and systemic and consist of basal cell carcinomas in various regions, odontogenic keratocistic tumors and skeletal anomalies, to name the most frequent. Despite the scarce medical literature on the topic, ocular involvement in this syndrome is frequent and at the level of various ocular structures. Our study focuses on the visual apparatus and its annexes in subjects with this syndrome, in order to better understand how this syndrome affects the ocular system, and to evaluate with greater accuracy and precision the nature of these manifestations in this group of patients. Results: Our study confirms the presence of the commonly cited ocular findings in the general literature regarding the syndrome [hypertelorism (45.5%), congenital cataract (18%), nystagmus (9%), colobomas (9%)] and highlights strabismus (63% of the patients), epiretinal membranes (36%) and myelinated optic nerve fiber layers (36%) as the most frequent ophthalmological findings in this group of patients. Conclusions: The presence of characteristic and frequent ocular signs in the Gorlin- Goltz syndrome could help with the diagnostic process in subjects suspected of having the syndrome who do not yet have a diagnosis. The ophthalmologist has a role as part of a multidisciplinary team in managing these patients. The ophthalmological follow-up that these patients require, can allow, if necessary, a timely therapy that could improve the visual prognosis of such patients