Three-Dimensional Axisymmetric Cloak Based on the Cancellation of Acoustic Scattering from a Sphere

L. Sanchis1, V. M. García-Chocano2, R. Llopis-Pontiveros1, A. Climente2, J. Martínez-Pastor1, F. Cervera2, and J. Sánchez-Dehesa2,
Sat Mar 30 2013 11:09:49 GMT+0300 (EAT)
This Letter presents the design, fabrication, and experimental characterization of a directional three-dimensional acoustic cloak for airborne sound. The cloak consists of 60 concentric acoustically rigid tori surrounding the cloaked object, a sphere of radius 4 cm. The major radii and positions of the tori along the symmetry axis are determined using the condition of complete cancellation of the acoustic field scattered from the sphere. They are obtained through an optimization technique that combines genetic algorithm and simulated annealing. The scattering cross section of the sphere with the cloak, which is the magnitude that is minimized, is calculated using the method of fundamental solutions. The low-loss fabricated cloak shows a reduction of the 90% of the sphere scattering cross section at the frequency of 8.55 kHz.

Roots and Associated Fungi Drive Long-Term Carbon Sequestration in Boreal Forest

K. E. Clemmensen1,*, A. Bahr2, O. Ovaskainen3, A. Dahlberg1,4, A. Ekblad5, H. Wallander2, J. Stenlid1, R. D. Finlay1, D. A. Wardle6, B. D. Lindahl1
Sat Mar 30 2013 11:08:13 GMT+0300 (EAT)
Boreal forest soils function as a terrestrial net sink in the global carbon cycle. The prevailing dogma has focused on aboveground plant litter as a principal source of soil organic matter. Using 14C bomb-carbon modeling, we show that 50 to 70% of stored carbon in a chronosequence of boreal forested islands derives from roots and root-associated microorganisms. Fungal biomarkers indicate impaired degradation and preservation of fungal residues in late successional forests. Furthermore, 454 pyrosequencing of molecular barcodes, in conjunction with stable isotope analyses, highlights root-associated fungi as important regulators of ecosystem carbon dynamics. Our results suggest an alternative mechanism for the accumulation of organic matter in boreal forests during succession in the long-term absence of disturbance.

The Biological Underpinnings of Namib Desert Fairy Circles

Norbert Juergens
Sat Mar 30 2013 11:07:08 GMT+0300 (EAT)
Abstract : The sand termite Psammotermes allocerus generates local ecosystems, so-called fairy circles, through removal of short-lived vegetation that appears after rain, leaving circular barren patches. Because of rapid percolation and lack of evapotranspiration, water is retained within the circles. This process results in the formation of rings of perennial vegetation that facilitate termite survival and locally increase biodiversity. This termite-generated ecosystem persists through prolonged droughts lasting many decades.

Permian paleoclimate data from fluid inclusions in halite

Kathleen Counter Benisona, b, , Robert H. Goldsteina
Sat Mar 30 2013 11:04:39 GMT+0300 (EAT)
Abstract : This study has yielded surface water paleotemperatures from primary fluid inclusions in mid Permian Nippewalla Group halite from western Kansas. A `cooling nucleation' method is used to generate vapor bubbles in originally all-liquid primary inclusions. Then, surface water paleotemperatures are obtained by measuring temperatures of homogenization to liquid. Homogenization temperatures ranged from 21°C to 50°C and are consistent along individual fluid inclusion assemblages, indicating that the fluid inclusions have not been altered by thermal reequilibration. Homogenization temperatures show a range of up to 26°C from base to top of individual cloudy chevron growth bands. Petrographic and fluid inclusion evidence indicate that no significant pressure correction is needed for the homogenization temperature data. We interpret these homogenization temperatures to represent shallow surface water paleotemperatures. The range in temperatures from base to top of single chevron bands may reflect daily temperatures variations. These Permian surface water temperatures fall within the same range as some modern evaporative surface waters, suggesting that this Permian environment may have been relatively similar to its modern counterparts. Shallow surface water temperatures in evaporative settings correspond closely to local air temperatures. Therefore, the Permian surface water temperatures determined in this study may be considered proxies for local Permian air temperatures.

Extremely high temperatures and paleoclimate trends recorded in Permian ephemeral lake halite

James J. Zambito IV and Kathleen C. Benison1James J. Zambito IV1 and Kathleen C. Benison
Sat Mar 30 2013 11:02:42 GMT+0300 (EAT)
Abstract : Although the late Paleozoic deglaciation is arguably one of the best deep-time analogs for current and predicted climate change, quantitative paleotemperature data from this interval are generally lacking. We reconstruct extreme paleoweather conditions and paleoclimate changes from Permian Nippewalla Group (probably uppermost Leonardian/Kungurian; North America) ephemeral lake halite by using fluid inclusion homogenization temperatures to directly measure the water temperature when the halite precipitated; in these depositional settings, this is an excellent air temperature proxy. Extremely high temperatures, to 73 °C, and large diurnal temperature ranges are evidenced in the lower Nippewalla Group, suggesting conditions more extreme than anywhere on Earth today. In contrast, the upper Nippewalla Group was cooler; maximum temperature was 43 °C and diurnal temperature ranges were smaller, though even these conditions are similar to modern extremely hot environments. Comparison to prior studies suggests that these results may be indicative of regional patterns. This study represents the first pre-Quaternary high-resolution quantitative data set of extreme paleoweather and possible paleoclimate trends from fluid inclusions in halite, and provides new insight into climate change during the late Paleozoic deglaciation.

Development of a Safety Culture Interaction (SCI) model for construction projects

Safety Science, Volume 57
Fri Mar 22 2013 13:54:50 GMT+0300 (EAT)
Abstract Fostering a positive safety culture is fundamental and critical for improving safety performance on a construction site. However, the complexity and evolutionary process of safety culture in a construction project team, which is different with other organizations, have not been well addressed and the basic model for construction project safety culture is still missing. The objectives of this paper are: (1) to put forward a distinct definition of construction project safety culture compared with the existing definitions of organizational safety culture, and (2) to propose a Safety Culture Interaction (SCI) Model, which demonstrates the evolvement of construction project safety culture and the specific interactive dynamism between owner, contractor and subcontractors in a project team as a temporary organization. A mixed approach of theoretical development and case-based development is applied. Intensive literature review on pertinent researches and the author’s experience are integrated in the theoretical model development to comprehend the characteristics of construction projects. A consulting project consists of safety climate survey and Behavior-Based Safety (BBS) implementation was conducted on two construction projects in Singapore to examine the theoretical model and elaborate the features of the model as the case-based development. Overall, the two-layer structure of the three constructs and the interactive dynamism of project safety culture are addressed in the model in consideration of the construction process, management practice, organization structure of project and the complicated site environments, which elaborate the concept of construction project safety culture, and provide a framework for safety culture study in construction.

Factors influencing success of wind-diesel hybrid systems in remote Alaska communities: Results of an informal survey

Renewable Energy, Volume 57
Thu Mar 21 2013 16:03:51 GMT+0300 (EAT)
In 2008, the Alaska State Legislature created and funded the Renewable Energy Fund (REF) grant program. As a result of this significant increase in available funding, the number of wind-diesel hybrid power systems is growing dramatically in rural Alaska. Development, integration, and operation of complex wind technologies in remote, rural communities are challenging. With multiple communities in Alaska installing and operating these systems, it is important to understand the factors that influence successful completion, operation and long-term maintenance of projects. As of December 2013, over $340 million has been spent constructing wind projects in 30 communities. The majority of these systems was built since 2008 and utilized over $50 million in appropriations from the REF by the Alaska legislature. This report summarizes the findings of an informal survey conducted on the most important characteristics of a successful wind-diesel hybrid power project in small remote rural communities. The survey was done to help guide socioeconomic research in Alaska on community capacity to ensure sustainable projects.

Protocol for maximizing energy savings and indoor environmental quality improvements when retrofitting apartments

Energy and Buildings, Volume 61
Thu Mar 21 2013 08:51:44 GMT+0300 (EAT)
The current focus on building energy retrofit provides an opportunity to simultaneously improve indoor environmental quality (IEQ). Toward this end, we developed a protocol for selecting packages of retrofits that both save energy and improve IEQ in apartments. The protocol specifies the methodology for selecting retrofits from a candidate list while addressing expected energy savings, IEQ impacts, and costs in an integrated manner. Interviews, inspections and measurements are specified to collect the needed input information. The protocol was applied to 17 apartments in three buildings in two different climates within California. Diagnostic measurements and surveys conducted before and after retrofit implementation indicate enhanced apartment performance.