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21.
Effect of coupling media on velocity and attenuation of ultrasonic waves in Brazilian wood 总被引:1,自引:0,他引:1
Raquel?Gon?alvesEmail author Alex?Julio?Trinca Gisleiva?Cristina?dos?Santos Ferreira 《Journal of Wood Science》2011,57(4):282-287
Coupling media are necessary to ensure that transducers bond to wood specimens to minimize coupling losses and improve the
accuracy of ultrasonic measurements. There are several types of coupling media available, and the optimal choice is not known.
In this work, we analyzed the results of ultrasonic wave attenuation for 0.1-MHz longitudinal and transverse transducers with
six different materials as coupling media in nine species of Brazilian wood with densities in the range 700–1170 kg/m3. Tests were performed using constant pressure on the transducer and with wave propagation in the longitudinal direction.
For transverse transducers, the polarization was in the radial and tangential directions. The results were analyzed statistically
and showed that, for attenuation in both longitudinal and transverse waves, the material used for coupling had significant
effects, whereas the wood species had no effect. For longitudinal waves, the statistical evaluation showed that the coupling
material performance was strongly dependent on the species of wood, but it was not possible to observe any tendency of behavior
associated with specific anatomical properties. 相似文献
22.
On the cause of the 1930s Dust Bowl 总被引:3,自引:0,他引:3
Schubert SD Suarez MJ Pegion PJ Koster RD Bacmeister JT 《Science (New York, N.Y.)》2004,303(5665):1855-1859
During the 1930s, the United States experienced one of the most devastating droughts of the past century. The drought affected almost two-thirds of the country and parts of Mexico and Canada and was infamous for the numerous dust storms that occurred in the southern Great Plains. In this study, we present model results that indicate that the drought was caused by anomalous tropical sea surface temperatures during that decade and that interactions between the atmosphere and the land surface increased its severity. We also contrast the 1930s drought with other North American droughts of the 20th century. 相似文献
23.
Schindler P Barreiro JT Monz T Nebendahl V Nigg D Chwalla M Hennrich M Blatt R 《Science (New York, N.Y.)》2011,332(6033):1059-1061
The computational potential of a quantum processor can only be unleashed if errors during a quantum computation can be controlled and corrected for. Quantum error correction works if imperfections of quantum gate operations and measurements are below a certain threshold and corrections can be applied repeatedly. We implement multiple quantum error correction cycles for phase-flip errors on qubits encoded with trapped ions. Errors are corrected by a quantum-feedback algorithm using high-fidelity gate operations and a reset technique for the auxiliary qubits. Up to three consecutive correction cycles are realized, and the behavior of the algorithm for different noise environments is analyzed. 相似文献
24.
Vásquez V Sotomayor M Cordero-Morales J Schulten K Perozo E 《Science (New York, N.Y.)》2008,321(5893):1210-1214
The mechanosensitive channel of small conductance (MscS) is a key determinant in the prokaryotic response to osmotic challenges. We determined the structural rearrangements associated with MscS activation in membranes, using functorial measurements, electron paramagnetic resonance spectroscopy, and computational analyses. MscS was trapped in its open conformation after the transbilayer pressure profile was modified through the asymmetric incorporation of lysophospholipids. The transition from the closed to the open state is accompanied by the downward tilting of the transmembrane TM1-TM2 hairpin and by the expansion, tilt, and rotation of the TM3 helices. These movements expand the permeation pathway, leading to an increase in accessibility to water around TM3. Our open MscS model is compatible with single-channel conductance measurements and supports the notion that helix tilting is associated with efficient pore widening in mechanosensitive channels. 相似文献
25.
Chimpanzees from the Tai forest of C?te d'Ivoire produce unintentional flaked stone assemblages at nut-cracking sites, leaving behind a record of tool use and plant consumption that is recoverable with archaeological methods. About 40 kilograms of nutshell and 4 kilograms of stone were excavated at the Panda 100 site. The data unearthed show that chimpanzees transported stones from outcrops and soils to focal points, where they used them as hammers to process foodstuff. The repeated use of activity areas led to refuse accumulation and site formation. The implications of these data for the interpretation of the earliest hominin archaeological record are explored. 相似文献
26.
Pederson GT Gray ST Woodhouse CA Betancourt JL Fagre DB Littell JS Watson E Luckman BH Graumlich LJ 《Science (New York, N.Y.)》2011,333(6040):332-335
In western North America, snowpack has declined in recent decades, and further losses are projected through the 21st century. Here, we evaluate the uniqueness of recent declines using snowpack reconstructions from 66 tree-ring chronologies in key runoff-generating areas of the Colorado, Columbia, and Missouri River drainages. Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains and in their north-south synchrony across the cordillera. Both the snowpack declines and their synchrony result from unparalleled springtime warming that is due to positive reinforcement of the anthropogenic warming by decadal variability. The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on streamflow and water supplies across the western United States. 相似文献
27.
Sonia Salvo Carlos Muñoz Julio Ávila Jaime Bustos Emilio Cariaga Carolina Silva Gabriel Vivallo 《Scientia Horticulturae》2011
Blueberry exporting is an important activity in Chile, with fresh blueberries commanding the highest prices and being among the most exported products to the European and North American markets. To maintain quality in the centres of consumption, farmers must continuously improve the logistics of harvesting and shipping the blueberries. Thus every year they must calculate the production of the orchard well in advance in order to hire staff and ensure the logistic cold chain. For this calculation they use a count of flower buds and a simple linear model of which the slope parameter represents the number of fruits per bud. However, due to the cost of the counting procedure, some producers count only a fraction of each plant (25%, 50% or 100%), and furthermore they do not know what effect the variety and productive age of the plants may have on the estimation. The objective of this work is to measure the impact of the cultivated variety, the age of the plant in productive years, and the percentage of fruits counted in estimating the parameter fruits per bud. The study involved monitoring 310 plants of different varieties and ages distributed in northern, central and southern Chile (over an area of approximately 700 km × 200 km). The parameter was estimated by fitting simple linear regression models (SLRM) as a function of the number of fruits and flower buds. To evaluate the impact on the parameter, the SLRM was fitted considering the variables observed in all the plants, by percentage counted, by variety and by variety-age of the plant. The major findings indicate significant differences in the estimation of the parameter, suggesting that in order to estimate fruits per bud the whole plant must be counted and its age and variety taken into account. 相似文献
28.
Julio Martin-Mata Raúl Moral Angel Torres-Climent Encarnación Martínez-Sabater Concepción Paredes 《Communications in Soil Science and Plant Analysis》2015,46(4):188-196
The aim of the present article is to show the possibilities of chemometric tools and the parallel factor analysis (PARAFAC) model, as well as to understand the complexities of the fluorescence emission-excitation matrix (EEM) of water-soluble organic matter (WSOM) extracted from sewage sludge samples obtained with different origins and stabilization procedures. The variation in the composition of WSOM in the different sewage sludge samples could be correlated with the conditions of stabilization; therefore, the use of fluorescence spectroscopy to monitor these changes can be a useful tool to optimize the management of this residual flux, avoiding environmental pollution. However, the “contour density” EEM maps obtained with fluorescence present continuous spectra with different peaks, valleys, and shoulders where manual peak picking can be complicated and subjective, especially in complex matrixes such as sewage sludge. With the PARAFAC algorithm, it is possible to resolve the emission and excitation spectra of the different fluorescence components present in the samples and their contribution to the total fluorescence. Also, the contribution (scores) of the different fluorophors can be coupled with another chemometric tool to provide an effective classification method using the stabilization conditions of sewage sludge as main criterion. In this study, a wide survey of sewage sludge samples (287) was characterized by fluorescence emission-excitation matrix. The final molecular composition of the sewage sludge samples was not related to the stabilization (aerobic vs anaerobic) treatments. However, a sewage sludge classification based on a combined spectroscopic-chemometric approach was obtained, which could be used for the optimization of sewage sludge use in agriculture, minimizing the environmental risks. 相似文献
29.
Patricio Arce Mauricio Moreno Mónica Gutierrez Marlene Gebauer Paola Dell’Orto Hebert Torres Ivette Acuña Pauline Oliger Alejandro Venegas Xavier Jordana Julio Kalazich Loreto Holuigue 《American Journal of Potato Research》1999,76(3):169-177
Blackleg and soft rot diseases, caused by the bacteriumErwinia carotovora, are among the diseases that cause important losses in culture and storage of potato. In this paper, we introduced bacterial resistance into potato, via genes encoding for proteins with antibacterial activity. For this purpose, potato clones were transformed either with the gene encoding the acidic attacin protein fromHyalophora cecropia, or with the gene encoding the cecropin analog peptide SB37. These clones were evaluated for soft rot and blackleg resistance, after inoculation with the bacterial strainErwinia carotovora subsp.atroseptica T7. Results reported in this paper indicate that a considerable percentage of the potato clones (15–22%) showed increased resistance to bacterial infection, revealed by reduced severity of blackleg or soft rot symptoms. Expression of the transgenes was demonstrated in some of the clones by Northern blot analysis. This is the first report indicating that expression of the gene encoding for an attacin protein and for the cecropin SB-37 peptide in transgenic potato confers increased resistance to bacterial infection. 相似文献
30.
Joanna Sobczyk Piotr Frączek Michał Obarzanowski Julio M. del Hoyo-Meléndez Łukasz Bratasz 《Wood Science and Technology》2014,48(5):981-994
Consolidation treatments are commonly employed in museum conservation studios for treating biologically deteriorated wooden cultural heritage objects. Impregnation using either a solvent/resin or a polymerizing system is an example of such an intervention, which is often difficult to describe in terms of its behavior within the object’s structure. A new simple method has been devised to evaluate the effectiveness of these impregnation treatments in terms of spatial distribution of consolidant solution. A combination of digital radiography and imaging analysis has permitted to evaluate the degree of penetration of a consolidant and to determine its location within the artifact by studying the X-ray images taken before, during, and after treatment. The adequacy of polymer solutions or their effectiveness as wood consolidants is properties which are often difficult to investigate due to limited visual access to the interior of the object. The proposed method provides an alternative way of studying these parameters through analysis of X-ray attenuation recorded on two images: taken before and after the conservation treatment. The resulting image is then converted into a two-dimensional map of consolidation agent within the object using a straightforward calibration procedure. 相似文献