Advances plasma sources for space applications

A Helicon thruster is an electrical propulsion system where the plasma source, i.e. Helicon source, is a dielectric tube surrounded by coils generating a weak magneto-static field (up to 0.15 T), and a radio frequency antenna working in the range of frequencies 1-50 MHz that drives the discharge. The propulsive figures of merit of a Helicon thruster (e.g. specific impulse) depend on plasma parameters (e.g. plasma density), that are in turn related to the power deposited by the antenna into the plasma. A similar plasma source can be exploited in gaseous plasma antennas, devices that rely on a partially or fully ionized gas to radiate electromagnetic waves. Plasma antennas might offer several advantages with respect to conventional antennas that make them suitable for space communications. As far as plasma antennas are concerned, their performances (e.g. gain) are related to the discharge parameters (i.e. the plasma density, the neutral pressure), and so to the efficiency of the plasma generation system. Regardless the differences in shape, field of application, and working condition, Helicon thrusters and plasma antennas share the same physical problems, namely: (i) wave propagation, (ii) power deposition, and (iii) transport of charged particles within the plasma source. To solve the wave-plasma coupling, we relied on ADAMANT, a full-wave frequency domain tool that takes into account the plasma effect as a polarization current. By means of this tool, we numerically assessed the radiation properties of the simplest plasma antenna configuration, a plasma dipole. We numerically verified that a plasma dipole can feature the same current distribution of a conventional metal dipole, and found that the plasma density, and the neutral pressure are the main parameters driving the plasma antenna performances. To understand the equilibrium conditions of a plasma source, we coupled ADAMANT with a 0-D fluid solver. This new numerical tool was exploited to design, and realize several custom-made plasma sources. This new approach allowed us to explore several combinations of gases, background pressures, and geometries without any constraints related to commercially available sources. By means of a microwave interferometer, we measured the plasma density, and its distribution along the sources. One of these sources was exploited in one of the very first prototypes of plasma antenna working in the GHz regime. The plasma dipole has been tested in an open environment for the gain pattern, and value; these results are in good accordance with the simulation results. Nevertheless, the maximum gain of the plasma dipole is lower by the 57% than the gain of a conventional dipole antenna in same conditions. This is due to a high pressure level, and a low plasma density of the source exploited in the plasma dipole, that lead to low conductance, and high losses within the plasma discharge

CONTROL OF MOTOR UNITS DURING VOLUNTARY FORCE-PRODUCTION: IMPLICATIONS FOR EXERCISE

We have recently developed a technology that enables studies of the firing properties of a large set (typically 30 to 40) of concurrently active motor units during isometric voluntary contractions ranging from low force levels to maximal voluntary contractions (MVC). With this technology we have executed studies to investigate the behavior of the firing rates of motor units as a function of their recruitment properties during contractions at various force levels. We found that the firing rates have a hierarchical structure wherein the firing rate value of motor units is inversely related to their recruitment threshold, with earlier recruited motor units having greater firing rates at any time and any force level during a contraction. This relationship does not support the opposite notion that has been generally held for the past five decades. Knowing the structure of the firing behavior of motor units during voluntary contractions provides guidance for understanding the performance of muscles during exercise and sports

Mammographic breast density in infertile and parous women

BACKGROUND: Mammographic breast density is a useful marker for breast cancer risk, as breast density is considered one of the strongest breast cancer risk factors. The study objective was to evaluate and compare mammographic breast density in infertile and parous women, as infertility may be associated with high breast density and cancer occurrence. METHODS: This study evaluated mammographic breast density using two different systems, BIRADS and Boyd. A selected patient population of 151 women with primary infertility (case group) was compared to 154 parous women who had at least one previous pregnancy (control group). Both groups were premenopausal women aged ≥ 35. RESULTS: Evaluation of mammographic features showed that 66.9% of case group patients and 53.9% of control group patients were classified BIRADS-3/BIRADS-4; p < 0.05. Adjusted Odds ratio for the case group in the categories BIRADS-3/BIRADS-4 was 1.78 (95% CI: 1.10-2.89). Using the Boyd classification system, 53.6% of case group patients and 31.8% of control group patients were classified E/F; p < 0.05. Adjusted Odds ratio for case group patients in Boyd categories E/F was 2.05 (95 % CI: 1.07-3.93). CONCLUSIONS: Both systems yielded a higher percentage of increased breast density in the case group. Boyd and BIRADS classification systems indicate to what extend breast cancer lesions may be missed on mammography due to masking by dense tissue. Therefore, patients with a high BIRADS or Boyd score should undergo further investigation

Comparative study of gene expression by cDNA microarray in human colorectal cancer tissues and normal mucosa

The causative molecular pathways underlying the pathogenesis of colorectal cancer (CRC) need to be better characterized. The purpose of our study was to better understand the genetic mechanism of oncogenesis for human colorectal cancer and to identify new potential tumor markers of use in clinical practice. We used cDNA microarrays to compare gene expression profiles of colorectal biopsies from 25 CRC patients and 13 normal mucosa from adjacent non-cancerous tissues. Findings were validated by real-time PCR; in addition, western blotting and immunochemistry analysis were carried out as further confirmation of differential expression at a protein level. Comparing cancerous tissues with normal colonic mucosa we identified 584 known genes differentially expressed to a significant degree (p<0.001). Many of the transcripts that were more abundant in tumors than in non-neoplastic tissues appear to reflect important events for colon carcinogenesis. For example, a significant number of these genes serve as apoptotic inhibitors (e.g. BFAR, BIRC1, BIRC6). Furthermore, we observed the simultaneous up-regulation of HLA-E and the down-regulation of beta2-microglobulin; these genes strongly support a potential tumor escape strategy from immune surveillance in colon cancer tissues. Our study provides new gene candidates in the pathogenesis of human CRC disease. From our results we hypothesize that CRC cells escape immune surveillance through a specific gene expression alteration; moreover, over-expression of several survival genes seems to confer a more anti-apoptotic phenotype. These genes are involved in pathways not previously implicated in CRC pathogenesis and they may provide new targets for therapy.Fil: Bianchini, Michele. Fundación P/la Invest.y Prevención del Cancer. Centro de Investigaciones Oncologicas; ArgentinaFil: Levy, Estrella Mariel. Fundación P/la Invest.y Prevención del Cancer. Centro de Investigaciones Oncologicas; Argentina. Universidad de Buenos Aires; ArgentinaFil: Zucchini, Cinzia. Università di Bologna; ItaliaFil: Pinski, Victor. Universidad de Buenos Aires; ArgentinaFil: Macagno, Carlo. Universidad de Buenos Aires; ArgentinaFil: De Sanctis, Paola. Università di Bologna; ItaliaFil: Valvassori, Luisa. Università di Bologna; ItaliaFil: Carinci, Paolo. Università di Bologna; ItaliaFil: Mordoh, Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina. Fundación P/la Invest.y Prevención del Cancer. Centro de Investigaciones Oncologicas; Argentin

Asimmetria del rischio sistematico dei titoli immobiliari americani: nuove evidenze econometriche

In this work we have found a relevant increase in the systematic risk of the American real estate securities in the year 2007 which go to the initial values in the year 2009. With the aim to evaluate the systematic risk we have used the Fama-French three factor model and we have studied the relationship between the extra-return of the REIT index where we have used as proxy the American real estate securities and the extra return of the S&P500 index representative by the market portfolio return. The results confirmed the presence of an “Asymmetric Beta Puzzle” in agreement with other previous studies. At the same time the results have shown that the REIT securities behaved as speculative securities. In the past the same securities were considered conservative in the year of the subprime crisis. The REIT securities in particular have amplified arriving to double the variations of the market risk premium

Asimmetria del rischio sistematico dei titoli immobiliari americani: nuove evidenze econometriche

In this work we have found a relevant increase in the systematic risk of the American real estate securities in the year 2007 which go to the initial values in the year 2009. With the aim to evaluate the systematic risk we have used the Fama-French three factor model and we have studied the relationship between the extra-return of the REIT index where we have used as proxy the American real estate securities and the extra return of the S&P500 index representative by the market portfolio return. The results confirmed the presence of an “Asymmetric Beta Puzzle” in agreement with other previous studies. At the same time the results have shown that the REIT securities behaved as speculative securities. In the past the same securities were considered conservative in the year of the subprime crisis. The REIT securities in particular have amplified arriving to double the variations of the market risk premium

Validation of the Treadmill Six-Minute Walk Test in People Following Cardiac Surgery

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Production of a yeast-free focaccia with reduced salt content using a selected Leuconostoc citreum strain and seawater

Abstract A biotechnological protocol to produce a focaccia (a typical Italian flat bread) without bakers' yeast addition and with reduced salt was developed, to meet the current needs of the consumer. Based on its leavening capability, the Leuconostoc citreum strain C2.27 was selected to be used as a starter instead of the baker's yeast and inoculated in a liquid sourdough (type-II) for the production of the "yeast-free" focaccia. The addition of different NaCl concentrations and the replacement of the salt with food grade seawater were evaluated, and the capability of the selected strain to affect technological, nutritional and sensory features of the focaccia investigated. A significant improvement of the nutritional characteristics of the focaccia was observed compared to the control (leavened with bakers' yeast and added with NaCl 1.5 g/100 g) using 0.7 g/100 g of salt in the form of NaCl or seawater. Besides the reduced Na content (66% lower than the control), focaccia with seawater also showed a higher content of Ca2+ and Mg2+ (ca. 36% and 53%, respectively), and the lowest predicted glycemic index compared to the other experimental focaccia