Development and Characterization of Multi-Alkali Antimonide Photocathodes for High-Brightness RF Photoinjectors.

Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium-potassium-antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in a high-gradient RF gun, DESY collaborated with INFN LASA to develop multi-alkali photocathode materials. In this report, we describe the recipe of K-Cs-Sb photocathodes, which were grown on a Mo substrate by varying the foundational Sb layer thickness using sequential deposition techniques. This report also illustrates the information regarding the film thickness, substrate temperature, deposition rate, and its possible effects on the photocathode's properties. In addition, the influence of temperature on the cathode degradation is also summarized. Furthermore, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of the K2CsSb material. The optical properties, such as dielectric function, reflectivity, refracting index, and extinction coefficient, were evaluated. The correlation between the calculated and measured optical properties, such as reflectivity, provides a better and more efficient strategy to rationalize and understand the photoemissive material's properties.

Fractal Geometry of Higher Derivative Gravity.

We determine the scaling properties of geometric operators such as lengths, areas, and volumes in models of higher derivative quantum gravity by renormalizing appropriate composite operators. We use these results to deduce the fractal dimensions of such hypersurfaces embedded in a quantum spacetime at very small distances.

Publisher's Note: Functional renormalization group approach to the Kraichnan model [Phys. Rev. E 92, 033016 (2015)].

This corrects the article DOI: 10.1103/PhysRevE.92.033016.

Functional renormalization group approach to the Kraichnan model.

We study the anomalous scaling of the structure functions of a scalar field advected by a random Gaussian velocity field, the Kraichnan model, by means of functional renormalization group techniques. We analyze the symmetries of the model and derive the leading correction to the structure functions considering the renormalization of composite operators and applying the operator product expansion.

Universal local symmetries and nonsuperposition in classical mechanics.

In the Hilbert space formulation of classical mechanics, pioneered by Koopman and von Neumann, there are potentially more observables than in the standard approach to classical mechanics. In this Letter, we show that actually many of those extra observables are not invariant under a set of universal local symmetries which appear once the Koopman and von Neumann formulation is extended to include the evolution of differential forms. Because of their noninvariance, those extra observables have to be removed. This removal makes the superposition of states in the Koopman and von Neumann formulation, and as a consequence also in classical mechanics, impossible.

[Gastrointestinal stromal tumour in emergency surgery]. / GIST intestinali nell'emergenza chirurgica.

Although rare, gastrointestinal stromal tumours (GIST) are the most common mesenchymal neoplasms of the gastrointestinal tract. We present our experience with the treatment of 8 patients affected by gastrointestinal stromal tumours of the ileum and colon. These cases were characterised by acute bleeding, intestinal obstruction or diffuse abdominal pain, and all of them underwent an emergency surgical treatment. We performed six partial resections of the ileum, one right hemicolectomy and one left hemicolectomy. Three patients died after surgical procedures for disease relapse, one died 10 years later due to other complications, and the others are still alive.

[Gastric mesenchymal tumours (GIST)]. / Tumori mesenchimali gastrici (GIST): aspetti clinici e revisione critica delle metodologie diagnostiche.

The incidence of gastrointestinal stromal tumours (GIST) has increased in recent years. A number of authors have attempted to define the actual nature of these tumours. Immunohistochemistry highlighting the positivity of tyrosine-kinase (CD117/c-Kit) has revealed the difference between gastrointestinal stromal tumours and other mesenchymal tumours and, therefore, the possibility of medical rather than surgical therapy. We retrospectively reviewed 19 patients affected by primary gastric GIST, who underwent surgery in recent years with subsequent follow-up. Gastroscopy and gastrointestinal tract radiography were used not only to obtain the diagnosis but also to establish the size, density, contours, ulceration, regional lymphadenopathy, mesenteric infiltration and the presence of metastases. The aim of this study was to evaluate the roles of endoscopy and radiology in this pathology and the advantages and limitations of each individual technique.