Does Long-Term Elevation of CO2 Concentration Increase Photosynthesis in Forest Floor Vegetation? (Indiana Strawberry in a Maryland Forest).

As the partial pressure of CO2 (pCO2) in the atmosphere rises, photorespiratory loss of carbon in C3 photosynthesis will diminish and the net efficiency of light-limited photosynthetic carbon uptake should rise. We tested this expectation for Indiana strawberry (Duchesnea indica) growing on a Maryland forest floor. Open-top chambers were used to elevate the pCO2 of a forest floor habitat to 67 Pa and were paired with control chambers providing an ambient pCO2 of 38 Pa. After 3.5 years, D. indica leaves grown and measured in the elevated pCO2 showed a significantly greater maximum quantum efficiency of net photosynthesis (by 22%) and a lower light compensation point (by 42%) than leaves grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O2, was the same for controls and plants grown at elevated pCO2. This showed that the maximum efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited photosynthesis at elevated pCO2 was simply a function of the decrease in photorespiration. Acclimation did decrease the ribulose-1,5-bisphosphate carboxylase/oxygenase and light-harvesting chlorophyll protein content of the leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO2 showed greater light-saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO2. In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO2, relative to controls, in both summer and fall. The increase in efficiency of light-limited photosynthesis with elevated pCO2 allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric pCO2

Low strength is related to diminished ground reaction forces and walking performance in older women

The purpose of this study was to determine how lower-limb strength in older women affected gait speed, supportive forces, spatial, and temporal aspects of walking gait. Twenty-four women between 65 – 80 yr performed maximal voluntary isometric contractions for the knee extensors (KE), knee flexors (KF), ankle plantarflexors (PF) and ankle dorsiflexors (DF) and were separated into low strength and normal strength groups using a KE torque threshold of 1.5 Nm kg−1 . They walked at both a standard speed of 0.8 m s−1 and at a self-selected maximal speed on an instrumented treadmill that recorded vertical ground reaction forces (vGRF) and spatiotemporal gait measures. Older women with low strength had 30% lower KE maximal torque, 36% lower PF maximal torque, 34% lower KE rate of torque development (RTD) and 30% lower KF RTD. Low strength women demonstrated slower maximal walking speeds (1.26 ± 0.20 vs. 1.56 ± 0.20 m s−1 ), lower vGRF during weight acceptance (1.15 ± 0.10 vs. 1.27 ± 0.13 BW), lower weight acceptance rates (11.3 ± 0.5 vs. 17.0 ± 5.5 BW s−1 ), slower stride rates, shorter stride lengths, and longer footground and double-limb support times (all P \u3c 0.05). Maximal gait speed was strongly correlated to peak vGRF and rate (r = 0.60 – 0.85, P \u3c 0.01) and moderately related to lower-limb strength (r = 0.42 – 0.60, P \u3c 0.05). In older women with low strength, diminished peak vGRFs were associated with slower walking speeds putting them at risk for mobility limitation, disability, poor health, and loss of independence

Fat mass limits lower-extremity relative strength and maximal walking performance in older women

The purpose of this study was to determine if excess fat negatively affects relative strength and walking gait performance in overweight, older women. Twenty five older women (65 – 80 yr) were separated into normal weight (BMI \u3c 25 kg m−2 , n=11) and overweight groups (BMI ≥ 25 kg m−2 , n=14). Strength and rate of torque development (RTD) of the knee extensors and flexors, ankle plantarflexors and dorsiflexors were measured. Participants walked at standard and maximal speeds during which muscle activation, spatiotemporal and kinetic gait variables were measured. Relative to mass, overweight older women had 24% lower maximal torque and 38% lower RTD than normal weight women. Maximal walking speed was slower in overweight (1.25 ± 0.22 m s−1 vs. 1.54 ± 0.25 m s−1 , P = 0.004) and was correlated to strength (r = 0.53, P \u3c 0.01) and fat mass (r = −0.65, P = 0.001). At maximal speed, overweight had 11% lower vertical ground reaction force relative to mass, 8% slower stride rate, 12% shorter strides, 13% longer foot-ground contact times, 21% longer double-limb support times, 65% greater knee extensor and 78% greater plantarflexor activation (P \u3c 0.05). Overweight, older women demonstrated altered gait and reduced walking performance related to poor relative strength and rate of torque development of lower-extremity muscles

Beads from the African Burial Ground, New York City: A Preliminary Assessment

Excavation of the African Burial Ground in New York City yielded the skeletal remains of more than 400 individuals. This paper is a preliminary discussion of beads associated with seven of the burials. The in situ bead configurations of three of the interments are distinctive and appear to be indicative of cultural practices of Africans in 18th-century New York. The configurations include necklaces and possibly wristlets, as well as waistbeads. The latter represent the first recorded instance of such use by Africans or African descendants in North America. These objects provide insight into the religious or ritual behavior of the people who utilized the burial ground

Compaction dynamics of a granular media under vertical tapping

We report new experimental results on granular compaction under consecutive vertical taps. The evolution of the mean volume fraction and of the mean potential energy of a granular packing presents a slow densification until a final steady-state, and is reminiscent to usual relaxation in glasses via a stretched exponential law. The intensity of the taps seems to rule the characteristic time of the relaxation according to an Arrhenius's type relation >. Finally, the analysis of the vertical volume fraction profile reveals an almost homogeneous densification in the packing.Comment: 7 pages, 4 figures, to appear in Europhysics Letter

Microrépartition des postlarves et des jeunes chez les crevettes pénéides de l'estuaire de l'Ambohinangy (baie d'Ambaro, Madagascar)

La répartition spatiale des post-larves, juvéniles et subadultes, de #Penaeus indicus et #Metapenaeus monoceros a été étudiée sur 5 km de l'estuaire de l'Ambohinangy, dans la baie d'Ambaro (nord-ouest de Madagascar). Les collectes de matériel biologique, associées à des mesures de paramètres environnementaux, ont été réalisées à la fin de la saison sèche (octobre 1989) et au début de la saison humide (novembre 1989). Les matrices de données ont été traitées par analyse factorielle des correspondances simple et multiple. En octobre, un gradient croissant de taille est observé de l'amont vers l'aval chez les deux espèces. Les post-larves et les petits juvéniles de #P. indicus sont situés globalement plus en amont que ceux de #M. monoceros. En novembre, le gradient de taille est moins marqué dans l'estuaire. Le courant lié à la typographie des stations et l'influence de la marée permettent d'expliquer la différence de comportement des deux espèces. #M. monoceros est inféodé aux zones à courants moyens ou faibles, à pentes faibles et fonds vaseux. #P. indicus est moins affecté par le courant et la nature du fond et paraît mieux réparti dans l'ensemble de la zone étudiée. (Résumé d'auteur

Scattering Mechanism in Modulation-Doped Shallow Two-Dimensional Electron Gases

We report on a systematic investigation of the dominant scattering mechanism in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron mobility versus density, mu \propto n^{alpha}, is extracted as a function of the 2DEG's depth. When shallower than 130 nm from the surface, the power-law exponent of the 2DEG, as well as the mobility, drops from alpha \simeq 1.65 (130 nm deep) to alpha \simeq 1.3 (60 nm deep). Our results for shallow 2DEGs are consistent with theoretical expectations for scattering by remote dopants, in contrast to the mobility-limiting background charged impurities of deeper heterostructures.Comment: 4 pages, 3 figures, modified version as accepted in AP

Pressure measurement in two-dimensional horizontal granular gases

International audienceA two-dimensional granular gas is produced by vibrating vertically a partial layer of beads on a horizontal plate. Measurements of the force applied by the granular gas to the sidewalls of the container, or granular pressure, are used to study the effect of the shaking strength, density, bead-plate restitution coefficient, and particle size on the steady properties of the gas

Out of Tune: Why Copyright Law Needs Music Lessons

This chapter offers a critical analysis of copyright law that integrates insights from music. The authors argue that the unique qualities of musical works magnify the mismatch between creative practices and copyright doctrine, and suggest that an interdisciplinary analysis can shine a revealing light on both the problem and potential paths to improvement. Beginning with an overview of copyright doctrine in Canada in respect of musical works and music infringement claims, the authors then borrow analytical concepts from the discipline of music theory to problematize copyright’s “reasonable listener” test for determining substantial copying. Using a specially-designed musical composition, the authors illustrate how and why this test may fail to perform its necessary role in the infringement analysis. The authors conclude by identifying some ways in which the legal analysis could be improved, including a more extensive use of both expert and survey evidence, and greater consideration of the accepted norms and practices of the relevant creative community. The overarching aim of this chapter is to demonstrate the importance of bringing the insights from musical and other creative disciplines to bear on the law of copyright, so that it might more accurately reflect the very practices it is meant to encourage