Calculation of electron interaction models in N2 and O2.

Cosmic rays have the potential to significantly affect the atmospheric composition by increasing the rate and changing the types of chemical reactions through ion production. The amount and states of ionization, and the spatial distribution of ions produced are still open questions for atmospheric models. To precisely estimate these quantities, it is necessary to simulate particle-molecule interactions, down to very low energies. Models enabling such simulations require interaction probabilities over a broad energy range and for all energetically allowed scattering processes. In this paper, we focus on electron interaction with the two most abundant molecules in the atmosphere, i.e., N2 and O2, as an initial step. A set of elastic and inelastic cross section models for electron transportation in oxygen and nitrogen molecules valid in the energy range 10 eV - 1 MeV, is presented. Comparison is made with available theoretical and experimental data and a reasonable good agreement is observed. Stopping power is calculated and compared with published data to assess the general consistency and reliability of our results. Good overall agreement is observed, with relative differences lower than 6% with the ESTAR database.

Characterization and optimization of a ß detector for 18F radio-guided surgery.

Radio-Guided Surgery (RGS) is a nuclear medicine technique to support the surgeon during surgery towards a complete tumor resection. It is based on intraoperative detection of radiation emitted by a radio-pharmaceutical that bounds selectively to tumoral cells. In the past years, an approach that exploits ß- emitting radiotracers has been pursued to overtake some limitations of the traditional RGS based on γ emission. A particle detector dedicated to this application, demonstrating very high efficiency to ß- particles and remarkable transparency to photons, has been thus developed. As a by-product, its characteristics suggested the possibility to utilize it with ß+ emitting sources, more commonly in use in nuclear medicine. In this paper, performances of such detector on 18F liquid sources are estimated by means of Monte Carlo simulations (MC) and laboratory measurements. The experimental setup with a 18F saline solution comprised a "positron signal" spot (a 7 × 10 mm cylinder representing the tumor residual), and a surrounding "far background" volume, that represented for the detector an almost isotropic source of annihilation photons. Experimental results show good agreement with MC predictions, thus confirming the expected performances of the detector with 18F, and the validity of the developed MC simulation as a tool to predict the gamma background determined by a diffuse source of annihilation photons.

Characterisation of a ß detector on positron emitters for medical applications.

PURPOSE: Radio Guided Surgery (RGS) is a technique that helps the surgeon to achieve an as complete as possible tumor resection, thanks to the intraoperative detection of particles emitted by a radio tracer that bounds to tumoral cells. In the last years, a novel approach to this technique has been proposed that, exploiting ß- emitting radio tracers, overtakes some limitations of established γ-RGS. In this context, a first prototype of an intraoperative ß particle detector, based on a high light yield and low density organic scintillator, has been developed and characterised on pure ß- emitters, like 90Y. The demonstrated very high efficiency to ß- particles, together with the remarkable transparency to photons, suggested the possibility to use this detector also with ß+ emitting sources, that have plenty of applications in nuclear medicine. In this paper, we present upgrades and optimisations performed to the detector to reveal such particles. METHODS: Laboratory measurement have been performed on liquid Ga68 source, and were used to validate and tune a Monte Carlo simulation. RESULTS: The upgraded detector has an ~80% efficiency to electrons above ~110keV, reaching a plateau value of ~95%. At the same time, the probe is substantially transparent to photons below ~200keV, reaching a plateau value of ~3%. CONCLUSIONS: The new prototype seems to have promising characteristics to perform RGS also with ß+ emitting isotopes.

Plasmon Controlled Shaping of Metal Nanoparticle Aggregates by Femtosecond Laser-Induced Melting.

In this work, we show how to control the morphology of femtosecond laser melted gold nanosphere aggregates. A careful choice of both laser fluence and wavelength makes it possible to selectively excite different aggregate substructures to produce larger spherical nanoparticles, nanorods, and nanoprisms or necklace-like 1D nanostructures in which the nanoparticles are interlinked by bridges. Finite integral technique calculations have been performed on the near-field concentration of light in the nanostructures which confirm the wavelength dependence of the light concentration and suggest that the resulting localized high intensities lead to nonthermal melting. We show that by tuning the wavelength of the melting light it is possible to choose the spatial extension of the ensembles of NPs heated thus allowing us to exhibit control over the morphology of the nanostructures formed by the melting process. By a proper combination of this method with self-assembly of chemically synthesized nanoparticles, one can envisage the development of an innovative high-throughput high-resolution nanofabrication technique.

Insights into 2- and 4(5)-Nitroimidazole Decomposition into Relevant Ions and Molecules Induced by VUV Ionization.

Nitromidazoles are relevant compounds of multidisciplinary interest, and knowledge of their physical-chemical parameters as well as their decomposition under photon irradiation is needed. Here we report an experimental and theoretical study of the mechanisms of VUV photofragmentation of 2- and 4(5)-nitromidazoles, compounds used as radiosensitizers in conjunction with radiotherapy as well as high-energy density materials. Photoelectron-photoion coincidence experiments, measurements of the appearance energies of the most important ionic fragments, density functional theory, and single-point coupled cluster calculations have been used to provide an overall insight into the energetics and structure of the different ionic/neutral products of the fragmentation processes. The results show that these compounds can be an efficient source of relevant CO, HCN, NO, and NO2 molecules and produce ions of particular astrophysical interest, like the isomers of azirinyl cation ( m/ z 40), predicted to exist in the interstellar medium, and protonated hydrogen cyanide ( m/ z 28).

An experimental and theoretical investigation of XPS and NEXAFS of 5-halouracils.

The C, N and O 1s excitation and ionization processes of 5X-uracil (X = F, Cl, Br, and I) were investigated using near edge X-ray absorption fine structure (NEXAFS) and X-ray photoemission (XPS) spectroscopies. This study aims at the fine assessment of the effects of the functionalization of uracil molecules by halogen atoms having different electronegativity and bound to the same molecular site. Two DFT-based approaches, which rely on different paradigms, have been used to simulate the experimental spectra and to assign the corresponding features. The analysis of the screening of the core holes of the different atoms via electronic charge density plots has turned out to be a useful tool to illustrate the competition between the partially aromatic and partially conjugate properties of this class of molecules.

Fragmentation of pure and hydrated clusters of 5Br-uracil by low energy carbon ions: observation of hydrated fragments.

The fragmentation of the isolated 5-bromouracil (5BrU) molecule and pure and nano-hydrated 5BrU clusters induced by low energy 12C4+ ions has been studied. A comparison indicates that the environment, on the one hand, protects the system against the complete break-up into small fragments, but, on the other hand, triggers 'new' pathways for fragmentation, for example the loss of the OH group. The most striking result is the observation of several series of hydrated fragments in the hydrated cluster case, with water molecules bound to hydrophilic sites of 5BrU. This highlights the strong interaction between 5BrU and water molecules and the blocking of specific fragmentation pathways, such as the loss of the BrC2H group for example.

Communication: "Position" does matter: The photofragmentation of the nitroimidazole isomers.

A combined experimental and theoretical approach has been used to disentangle the fundamental mechanisms of the fragmentation of the three isomers of nitroimidazole induced by vacuum ultra-violet (VUV) radiation, namely, 4-, 5-, and 2-nitroimidazole. The results of mass spectrometry as well as photoelectron-photoion coincidence spectroscopy display striking differences in the radiation-induced decomposition of the different nitroimidazole radical cations. Based on density functional theory (DFT) calculations, a model is proposed which fully explains such differences, and reveals the subtle fragmentation mechanisms leading to the release of neutral species like NO, CO, and HCN. Such species have a profound impact in biological media and may play a fundamental role in radiosensitising mechanisms during radiotherapy.

Site- and state-selected photofragmentation of 2Br-pyrimidine.

The fragmentation of the 2Br-pyrimidine molecule following direct valence photoionization or inner shell excitation has been studied by electron-ion coincidence experiments. 2Br-pyrimidine has been chosen as a model for the class of pyrimidinic building blocks of three nucleic acids and several radiosensitizers. It is known that the site- and state-localization of energy deposition, typical of inner shell excitation, results in the enhancement of the total ion yield as well as in changes in the relative intensity of the different fragmentation channels. Here we address the question of the origin of this selective fragmentation by using electron-ion coincidence techniques. The results show that the fragmentation is strongly selective in the final singly charged ion state, independently of the process that leads to the population of that state, and the dominant fragmentation patterns correlate with the nearest appearance potential.

The sensitivity and specificity of the Middlesex Elderly Assessment of Mental State (MEAMS) for detecting cognitive impairment after stroke.

The aim of the study was to assess the sensitivity and specificity of the MEAMS (Golding, 1989) for detecting cognitive impairment after stroke. Stroke patients admitted to hospital received a cognitive screening assessment, the MEAMS, and a detailed cognitive assessment. The information obtained from the detailed assessment was summarised in a structured written report. From the conclusions in these reports, patients were classified as "impaired" or "not impaired" in perception, memory, executive function and language. The sensitivity and specificity of the MEAMS subtests and the overall number of tests passed were determined in relation to the presence of impairment, as given in the overall conclusion of the written reports. There were 30 stroke patients, aged 58 to 92 (mean 75.80, SD 7.94) years. Of these, 17 were men and 13 were women. The sensitivity of the MEAMS subtests ranged from 11% to 100% and the specificity ranged from 69% to 100%. The sensitivity of the overall MEAMS score was 52% and the specificity was 100%, using a cut-off score of 3 or more fails to indicate impairment. Three subtests, Orientation, Naming and Unusual views had 81% sensitivity and 50% specificity for detecting problems in language, perception or memory. The MEAMS was not a sensitive screen for overall cognitive impairment or for memory, perceptual, language, or executive function problems after stroke, but it was specific. Although screening for cognitive impairment is important, the MEAMS is not recommended as the sole method, as it produces an unacceptably high false negative rate. Three subtests (Orientation, Naming and Unusual views) had 81% sensitivity and 50% specificity for detecting cognitive problems in language, perception or memory after stroke.

Anandamide degradation and N-acylethanolamines level in wild-type and CB1 cannabinoid receptor knockout mice of different ages.

CD1 mice lacking the CB1 receptors (knockout, KO) were compared with wild-type littermates for their ability to degrade N-arachidonoylethanolamine (anandamide, AEA) through a membrane transporter (AMT) and a fatty acid amide hydrolase (FAAH). The regional distribution and age-dependence of AMT and FAAH activity were investigated. Anandamide membrane transporter and FAAH increased with age in knockout mice, whereas they showed minor changes in wild-type animals. Remarkably, they were higher in all brain areas of 6-month-old knockout versus wild-type mice, and even higher in 12-month-old animals. The molecular mass (approximately 67 kDa) and isoelectric point (approximately 7.6) of mouse brain FAAH were determined and the FAAH protein content was shown to parallel the enzyme activity. The kinetic constants of AMT and FAAH in the cortex of wild-type and knockout mice at different ages suggested that different amounts of the same proteins were expressed. The cortex and hippocampus of wild-type and knockout mice contained the following N-acylethanolamines: AEA (8% of total), 2-arachidonoylglycerol (5%), N-oleoylethanolamine (20%), N-palmitoylethanolamine (53%) and N-stearoylethanolamine (14%). These compounds were twice as abundant in the hippocampus as in the cortex. Minor differences were observed in AEA or 2-arachidonoylglycerol content in knockout versus wild-type mice, whereas the other compounds were lower in the hippocampus of knockout versus wild-type animals.

Gas chromatography-mass spectrometry analysis of endogenous cannabinoids in healthy and tumoral human brain and human cells in culture.

Endocannabinoids are lipid mediators thought to modulate central and peripheral neural functions. We report here gas chromatography-electron impact mass spectrometry analysis of human brain, showing that lipid extracts contain anandamide and 2-arachidonoylglycerol (2-AG), the most active endocannabinoids known to date. Human brain also contained the endocannabinoid-like compounds N-oleoylethanolamine, N-palmitoylethanolamine and N-stearoylethanolamine. Anandamide and 2-AG (0.16 +/- 0.05 and 0.10 +/- 0.05 nmol/mg protein, respectively) represented 7.7% and 4.8% of total endocannabinoid-like compounds, respectively. N-Palmitoyethanolamine was the most abundant (50%), followed by N-oleoyl (23.6%) and N-stearoyl (13.9%) ethanolamines. A similar composition in endocannabinoid-like compounds was found in human neuroblastoma CHP100 and lymphoma U937 cells, and also in rat brain. Remarkably, human meningioma specimens showed an approximately six-fold smaller content of all N-acylethanolamines, but not of 2-AG, and a similar decrease was observed in a human glioblastoma. These ex vivo results fully support the purported roles of endocannabinoids in the nervous system.