SRI International

About: SRI International is a nonprofit organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Ionosphere & Laser. The organization has 7222 authors who have published 13102 publications receiving 660724 citations. The organization is also known as: Stanford Research Institute & SRI.

MRI estimates of brain iron concentration in normal aging: Comparison of field-dependent (FDRI) and phase (SWI) methods

Abstract: Different brain structures accumulate iron at different rates throughout the adult life span. Typically, striatal and brain stem structures are higher in iron concentrations in older than younger adults, whereas cortical white matter and thalamus have lower concentrations in the elderly than young adults. Brain iron can be measured in vivo with MRI by estimating the relaxivity increase across magnetic field strengths, which yields the Field-Dependent Relaxation Rate Increase (FDRI) metric. The influence of local iron deposition on susceptibility, manifests as MR phase effects, forms the basis for another approach for iron measurement, Susceptibility-Weighted Imaging (SWI), for which imaging at only one field strength is sufficient. Here, we compared the ability of these two methods to detect and quantify brain iron in 11 young (5 men, 6 women; 21 to 29 years) and 12 elderly (6 men, 6 women; 64 to 86 years) healthy adults. FDRI was acquired at 1.5 T and 3.0 T, and SWI was acquired at 1.5 T. The results showed that both methods detected high globus pallidus iron concentration regardless of age and significantly greater iron in putamen with advancing age. The SWI measures were more sensitive when the phase signal intensities themselves were used to define regions of interest, whereas FDRI measures were robust to the method of region of interest selection. Further, FDRI measures were more highly correlated than SWI iron estimates with published postmortem values and were more sensitive than SWI to iron concentration differences across basal ganglia structures. Whereas FDRI requires more imaging time than SWI, two field strengths, and across-study image registration for iron concentration calculation, FDRI appears more specific to age-dependent accumulation of non-heme brain iron than SWI, which is affected by heme iron and non-iron source effects on phase.

New horizons for orthotic and prosthetic technology: artificial muscle for ambulation

Abstract: The rehabilitation community is at the threshold of a new age in which orthotic and prosthetic devices will no longer be separate, lifeless mechanisms, but intimate extensions of the human body-structurally, neurologically, and dynamically. In this paper we discuss scientific and technological advances that promise to accelerate the merging of body and machine, including the development of actuator technologies that behave like muscle and control methodologies that exploit principles of biological movement. We present a state-of-the-art device for leg rehabilitation: a powered ankle-foot orthosis for stroke, cerebral palsy, or multiple sclerosis patients. The device employs a forcecontrollable actuator and a biomimetic control scheme that automatically modulates ankle impedance and motive torque to satisfy patient-specific gait requirements. Although the device has some clinical benefits, problems still remain. The force-controllable actuator comprises an electric motor and a mechanical transmission, resulting in a heavy, bulky, and noisy mechanism. As a resolution of this difficulty, we argue that electroactive polymer-based artificial muscle technologies may offer considerable advantages to the physically challenged, allowing for joint impedance and motive force controllability, noise-free operation, and anthropomorphic device morphologies.

Temperature responses of antennal receptors of the mosquito,Aedes aegypti

Abstract: 1. A pair of thermoreceptor units was identified in the sensilla coeloconica at the tip of the antennae on the mosquito,Aedes aegypti. 2. One thermoreceptor was warm-sensitive and responded with a phasic-tonic increase in spike frequency to sudden increases in temperature. The second thermoreceptor was coldsensitive, responding with a phasic-tonic increase in spike activity to sudden decreases in temperature. 3. The mean tonic spike activity of both the cold and warm receptors increased with increasing temperature to a peak of 30 imp/sec at 26‡ C for the cold receptor and 35 imp/sec at 28.5‡ C for the warm receptor. The tonic activity declined as the temperature was increased further. The maximum phasic sensitivity was observed with small temperature changes (δ T = ± 0.2‡C). This was 136 imp/sec/‡C temperature drop in the cold receptor and 130 imp/ sec/‡ C rise in the warm receptor. 4. The importance of temperature in the host-seeking and “attack” behavior of the mosquito is discussed.