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51.
52.
A. Farmer R. Rye G. Landis C. Bern C. Kester I. Ridley 《Isotopes in environmental and health studies》2013,49(3):169-177
We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and (2) analyzing the deuterium and 18O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (δ13C, δ15N and δ34S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, δ34S was most important, followed by δ15N, and then δ13C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis δ13C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both δD and δ18O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the δD and δ18O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local δD and δ18O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues. 相似文献
53.
Patricia B. da Silva Paulo H. Terra Regina C. G. Frem Adelino V. G. Netto Antonio E. Mauro 《Journal of Thermal Analysis and Calorimetry》2011,103(2):495-499
In the present contribution, a procedure to estimate parameters using non-isothermal data was applied. The estimation procedure
is based on the use of an energy balance in DSC furnace. The approach found all kinetic parameters of autocatalytic model
(E
1, E
2, A
1, A
2, m, n) besides the ultimate reaction heat and their confidence regions by using deterministic and heuristic algorithms. The application
of this approach to isothermal data was done in a previous work and similar results were obtained. The results show that the
use of an energy balance is a good methodology to estimate cure kinetic parameters of non-isothermal experiments. 相似文献
54.
Spontaneous emission and the inelastic scattering of photons are two natural processes usually associated with decoherence and the reduction in the capacity to process quantum information. Here we show that, when suitably detected, these photons are sufficient to build all the fundamental blocks needed to perform quantum computation in the emitting qubits while protecting them from deleterious dissipative effects. We exemplify this by showing how to efficiently prepare graph states for the implementation of measurement-based quantum computation. 相似文献
55.
56.
Terra Sztain Ashay Patel D. John Lee Tony D. Davis J. Andrew McCammon Michael D. Burkart 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(32):11004-11008
At the center of many complex biosynthetic pathways, the acyl carrier protein (ACP) shuttles substrates to appropriate enzymatic partners to produce fatty acids and polyketides. Carrier proteins covalently tether their cargo via a thioester linkage to a phosphopantetheine cofactor. Due to the labile nature of this linkage, chemoenzymatic methods have been developed that involve replacement of the thioester with a more stable amide or ester bond. We explored the importance of the thioester bond to the structure of the carrier protein by using solution NMR spectroscopy and molecular dynamics simulations. Remarkably, the replacement of sulfur with other heteroatoms results in significant structural changes, thus suggesting more rigorous selections of isosteric substitutes is needed. 相似文献
57.
58.
Jessa Marie V. Makabenta Jungmi Park Cheng-Hsuan Li Aritra Nath Chattopadhyay Ahmed Nabawy Ryan F. Landis Akash Gupta Suzannah Schmidt-Malan Robin Patel Vincent M. Rotello 《Molecules (Basel, Switzerland)》2021,26(16)
Biofilm infections are a global public health threat, necessitating new treatment strategies. Biofilm formation also contributes to the development and spread of multidrug-resistant (MDR) bacterial strains. Biofilm-associated chronic infections typically involve colonization by more than one bacterial species. The co-existence of multiple species of bacteria in biofilms exacerbates therapeutic challenges and can render traditional antibiotics ineffective. Polymeric nanoparticles offer alternative antimicrobial approaches to antibiotics, owing to their tunable physico-chemical properties. Here, we report the efficacy of poly(oxanorborneneimide) (PONI)-based antimicrobial polymeric nanoparticles (PNPs) against multi-species bacterial biofilms. PNPs showed good dual-species biofilm penetration profiles as confirmed by confocal laser scanning microscopy. Broad-spectrum antimicrobial activity was observed, with reduction in both bacterial viability and overall biofilm mass. Further, PNPs displayed minimal fibroblast toxicity and high antimicrobial activity in an in vitro co-culture model comprising fibroblast cells and dual-species biofilms of Escherichia coli and Pseudomonas aeruginosa. This study highlights a potential clinical application of the presented polymeric platform. 相似文献
59.
F. Szmulowicz J. Ehret K. Mahalingam S. Hegde J. Solomon D. H. Tomich G. Landis G. J. Brown T. Oogarah H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):331-336
Bound-to-continuum normal-incidence absorption in p-type GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) is strongest when the second light-hole (LH2) level is resonant with the top of the valence band QW. However, we found that such absorption saturates as a function of doping in the well. Using the envelope-function model (EFA), this paper shows that moving the LH2 resonance slightly deeper into the continuum avoids absorption saturation and produces optimal p-QWIP response. A suitable set of mid-IR samples was grown to test this conjecture and their photoresponse measured. The results indicate that absorption can be more than doubled through the use of the new p-QWIP designs. This result is explained by showing that the line of resonances in the continuum as a function of the in-plane wave vector eventually becomes a bound LH2 band in the well at some critical wave vector. Therefore, it is possible to avoid absorption saturation by matching this critical wave vector (i.e., well width and/or well depth) with the Fermi wave vector (i.e., doping in the well) for the desired QWIP (i.e., cutoff wavelength). 相似文献
60.
Seymour Meyerson Catherine Fenselau J. L. Young W. R. Landis Edward Selke L. C. Leitch 《Journal of mass spectrometry : JMS》1970,3(6):689-707
The mass spectra of hexanal, heptanal and nonanal variously labeled with deuterium confirm γ-hydrogen migration and β cleavage as the mechanism leading to [C2H4O]+˙ and [M ? C2H4O]+˙, although the data on the latter are complicated by contributions from other, related paths. In addition, they show that three other major primary decomposition products, [M ? C2H4]+˙, [M ? H2O]+˙ and [C3H5O]+, all arise in large part by processes involving γ-hydrogen migration to the oxygen atom. The ethylene lost to yield the first of these products consists of the α and β methylene groups. The loss of ethylene most likely occurs by way of a cyclobutanol intermediate, which, via alternative reaction paths, may well contribute to the yields of the other two products as well. These findings further extend the range of parallelism between photochemical and electron-impact-induced reactions. 相似文献