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.

Longitudinal Study of Callosal Microstructure in the Normal Adult Aging Brain Using Quantitative DTI Fiber Tracking

Abstract: We present a review of neuroimaging studies of normal adult aging conducted with diffusion tensor imaging (DTI) and data from one of the first longitudinal studies using DTI to study normal aging. To date, virtually all DTI studies of normal adult aging have been cross-sectional and have identified several patterns of white matter microstructural sparing and compromise that differentiate regional effects, fiber type, and diffusivity characteristics: (1) fractional anisotropy (FA) is lower and mean diffusivity is higher in older than younger adults, (2) aging is characterized by an anterior-to-posterior gradient of greater-to-lesser compromise also seen in superior-to-inferior fiber systems, and (3) association fibers connecting cortical sites appear to be more vulnerable to aging than projection fibers. The results of this longitudinal study of the macrostructure and microstructure of the corpus callosum yielded a consistent pattern of differences between healthy, young (20s to 30s) and elderly (60s to 70s) men and women without change over 2 years. We then divided the fibers of the corpus callosum into the midsagittal strip and the lateral distal fibers in an attempt to identify the locus of the age-related differences. The results indicated that, on average, mean values of FA and longitudinal diffusivity (lambdaL) were lower in the distal than midsagittal fibers in both groups, but the age effects and the anterior-to-posterior gradients were more pronounced for the distal than midsagittal fibers and extended more posteriorly in the distal than midsagittal fibers. Despite lack of evidence for callosal aging over 2 years, ventricular enlargement occurred and was disproportionately greater in the elderly relative to the young group, being 8.2% in the elderly but only 1.2% in the young group. Thus, different brain regions can express different rates of change with aging. Our longitudinal DTI data indicate that normal aging is associated with declining FA and increasing diffusivity in both lambdaL (longitudinal diffusivity) and lambdaT (transverse diffusivity), perhaps defining the normal ontological condition rather than a pathological one, which can be marked by low FA and low diffusivity.

Methods and apparatus for scalable, distributed management of virtual private networks

Abstract: A groupware management system for collaborative groups is disclosed that is scalable to support large, dynamic, multiple, and other virtual VPNs. The system may introduce a graph (or hierarchical) structure to the VPN, providing multiple master nodes controlling membership in subsets of the collaborative group. Use of multiple master nodes in a graph-structured (or hierarchical) network topology often relaxes the need for a single, centralized, globally consistent view of VPN group membership, and enables distribution of the management burden among multiple master nodes. Membership in the VPN may be changed dynamically by the second master node for the member nodes of the second subset, without requiring the first master node to dynamically update its group membership records to reflect the change and in many cases without even having to notify the first master node (and vice versa), for example. In further embodiments, the use of multiple master nodes may increase the reliability and efficiency of VPNs, such as by enabling load balancing of master node tasks. Fail-over mechanisms may also be used to transparently re-route management tasks to an alternate master node especially in the case of failure of the current master node serving a given member node.

An algorithm for reasoning about equality

Abstract: A simple technique for reasoning about equalities that is fast and complete for ground formulas with function symbols and equality is presented. A proof of correctness is given as well.

Sequence alterations using homologous recombination

Abstract: The invention relates to methods for targeting an exogenous polynucleotide or exogenous complementary polynucleotide pair to a predetermined endogenous DNA target sequence in a target cell by homologous pairing, particularly for altering an endogenous DNA sequence, such as a chromosomal DNA sequence, typically by targeted homologous recombination. In certain embodiments, the invention relates to methods for targeting an exogenous polynucleotide having a linked chemical substituent to a predetermined endogenous DNA sequence in a metabolically active target cell, generating a DNA sequence-specific targeting of one or more chemical substituents in an intact nucleus of a metabolically active target cell, generally for purposes of altering a predetermined endogenous DNA sequence in the cell. The invention also relates to compositions that contain exogenous targeting polynucleotides, complementary pairs of exogenous targeting polynucleotides, chemical substituents of such polynucleotides, and recombinase proteins used in the methods of the invention.