Shapes of leading tunnelling trajectories for single-electron molecular ionization

Based on the geometrical approach to tunnelling by P.D. Hislop and I.M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single-active-electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and "almost" linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the obtained results are discussed.Comment: 14 pages, 5 figure

Splines and Wavelets on Geophysically Relevant Manifolds

Analysis on the unit sphere $\mathbb{S}^{2}$ found many applications in seismology, weather prediction, astrophysics, signal analysis, crystallography, computer vision, computerized tomography, neuroscience, and statistics. In the last two decades, the importance of these and other applications triggered the development of various tools such as splines and wavelet bases suitable for the unit spheres $\mathbb{S}^{2}$, $\>\>\mathbb{S}^{3}$ and the rotation group $SO(3)$. Present paper is a summary of some of results of the author and his collaborators on generalized (average) variational splines and localized frames (wavelets) on compact Riemannian manifolds. The results are illustrated by applications to Radon-type transforms on $\mathbb{S}^{d}$ and $SO(3)$.Comment: The final publication is available at http://www.springerlink.co

High-dose chemoradiotherapy followed by surgery versus surgery alone in esophageal cancer: a retrospective cohort study

<p>Abstract</p> <p>Background</p> <p>We aimed to assess whether high-dose preoperative chemoradiotherapy (CRT) improves outcome in esophageal cancer patients compared to surgery alone and to define possible prognostic factors for overall survival.</p> <p>Methods</p> <p>Hundred-and-seven patients with disease stage IIA - III were treated with either surgery alone (n = 45) or high-dose preoperative CRT (n = 62). The data were collected retrospectively. Sixty-seven patients had adenocarcinomas, 39 squamous cell carcinomas and one undifferentiated carcinoma. CRT was given as three intensive chemotherapy courses by cisplatin 100 mg/m²on day 1 and 5-fluorouracil 1000 mg/m²/day, from day 1 through day 5 as continuous infusion. One course was given every 21 days. The last two courses were given concurrent with high-dose radiotherapy, 2 Gy/fraction and a median dose of 66 Gy. Kaplan-Meier survival analysis with log rank test was used to obtain survival data and Cox Regression multivariate analysis was used to define prognostic factors for overall survival.</p> <p>Results</p> <p>Toxicity grade 3 of CRT occurred in 30 (48.4%) patients and grade 4 in 24 (38.7%) patients of 62 patients. One patient died of neutropenic infection (grade 5). Fifty percent (31 patients) in the CRT group did undergo the planned surgery. Postoperative mortality rate was 9% and 10% in the surgery alone and CRT+ surgery groups, respectively (p = 1.0). Median overall survival was 11.1 and 31.4 months in the surgery alone and CRT+ surgery groups, respectively (log rank test, p = 0.042). In the surgery alone group one, 3 and 5 year survival rates were 44%, 24% and 16%, respectively and in the CRT+ surgery group they were 68%, 44% and 29%, respectively. By multivariate analysis we found that age of patient, performance status, alcoholism and > = 4 pathological positive lymph nodes in resected specimen were significantly associated with overall survival, whereas high-dose preoperative CRT was not.</p> <p>Conclusion</p> <p>We found no significant survival advantage in esophageal cancer stage IIA-III following preoperative high-dose CRT compared to surgery alone. Patient's age, performance status, alcohol abuse and number of positive lymph nodes were prognostic factors for overall survival.</p

Influence of gas atmosphere (Ar or He) on the laser powder bed fusion of a Ni-based alloy

The gaseous atmosphere plays a major role in the quality of the manufactured parts in Laser Powder Bed Fusion (L-PBF) by protecting the metal from high temperature oxidation. If argon and nitrogen are the most commonly used gases, helium has almost never been considered as a possible candidate as a chemically inert shielding gas. To provide a better understanding of the influence of the gas atmosphere on the process stability, a comparative study of L-PBF manufacturing under argon and helium atmospheres has been carried out, considering a nickel-based alloy Inconel® 625 and a single bead configuration. To this end, in-situ process measurements were carried out on a dedicated experimental setup. The melt pool behaviour, the expansion of the vapour plume and the amount of spatters were evaluated with high-speed imaging for the two gases considered, together with the final L-PBF bead dimensions. Results were also compared to single fusion beads carried out in an industrial L-PBF machine for a comparable range of volume energy densities. The influence of the shielding atmosphere on L-PBF single beads was as follows: (1) dimensions of beads were shown to be constant whatever the gas; (2) fewer and smaller spatters were produced under helium atmosphere, especially for high volume energy densities. Physical mechanisms were then discussed to understand those specific effects

Climate change, precipitation and impacts on an estuarine refuge from disease

© The Author(s), 2011. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 6 (2011): e18849, doi:10.1371/journal.pone.0018849.Oysters play important roles in estuarine ecosystems but have suffered recently due to overfishing, pollution, and habitat loss. A tradeoff between growth rate and disease prevalence as a function of salinity makes the estuarine salinity transition of special concern for oyster survival and restoration. Estuarine salinity varies with discharge, so increases or decreases in precipitation with climate change may shift regions of low salinity and disease refuge away from optimal oyster bottom habitat, negatively impacting reproduction and survival. Temperature is an additional factor for oyster survival, and recent temperature increases have increased vulnerability to disease in higher salinity regions. We examined growth, reproduction, and survival of oysters in the New York Harbor-Hudson River region, focusing on a low-salinity refuge in the estuary. Observations were during two years when rainfall was above average and comparable to projected future increases in precipitation in the region and a past period of about 15 years with high precipitation. We found a clear tradeoff between oyster growth and vulnerability to disease. Oysters survived well when exposed to intermediate salinities during two summers (2008, 2010) with moderate discharge conditions. However, increased precipitation and discharge in 2009 reduced salinities in the region with suitable benthic habitat, greatly increasing oyster mortality. To evaluate the estuarine conditions over longer periods, we applied a numerical model of the Hudson to simulate salinities over the past century. Model results suggest that much of the region with suitable benthic habitat that historically had been a low salinity refuge region may be vulnerable to higher mortality under projected increases in precipitation and discharge. Predicted increases in precipitation in the northeastern United States due to climate change may lower salinities past important thresholds for oyster survival in estuarine regions with appropriate substrate, potentially disrupting metapopulation dynamics and impeding oyster restoration efforts, especially in the Hudson estuary where a large basin constitutes an excellent refuge from disease.Funding was provided by the Hudson River Foundation, grant number 00607A, and the New York State Department of Environmental Conservation (MOU 2008)

Rising from the Sea: Correlations between Sulfated Polysaccharides and Salinity in Plants

High salinity soils inhibit crop production worldwide and represent a serious agricultural problem. To meet our ever-increasing demand for food, it is essential to understand and engineer salt-resistant crops. In this study, we evaluated the occurrence and function of sulfated polysaccharides in plants. Although ubiquitously present in marine algae, the presence of sulfated polysaccharides among the species tested was restricted to halophytes, suggesting a possible correlation with salt stress or resistance. To test this hypothesis, sulfated polysaccharides from plants artificially and naturally exposed to different salinities were analyzed. Our results revealed that the sulfated polysaccharide concentration, as well as the degree to which these compounds were sulfated in halophytic species, were positively correlated with salinity. We found that sulfated polysaccharides produced by Ruppia maritima Loisel disappeared when the plant was cultivated in the absence of salt. However, subjecting the glycophyte Oryza sativa Linnaeus to salt stress did not induce the biosynthesis of sulfated polysaccharides but increased the concentration of the carboxylated polysaccharides; this finding suggests that negatively charged cell wall polysaccharides might play a role in coping with salt stress. These data suggest that the presence of sulfated polysaccharides in plants is an adaptation to high salt environments, which may have been conserved during plant evolution from marine green algae. Our results address a practical biological concept; additionally, we suggest future strategies that may be beneficial when engineering salt-resistant crops