Silicon implantation in GaAs

The electrical properties of room-temperature Si implants in GaAs have been studied. The implantations were done at 300 keV with doses ranging from 1.7×10^13 to 1.7×10^15 cm^–2. The implanted samples were annealed with silicon nitride encapsulants in H2 atmosphere for 30 min at temperatures ranging from 800 to 900°C to electrically activate the implanted ions. Results show that the implanted layers are n type, which implies that the Si ions preferentially go into Ga sites substitutionally. For low-dose implants, high (~90%) electrical activation of the implanted ions is achieved and the depth distribution of the free-electron concentration in the implanted layer roughly follows a Gaussian. However, for high-dose implants, the activation is poor (<15% for a 900 °C anneal) and the electron concentration profile is flat and deeper than the expected range

Semi-groups, groups and Lyapunov stability of partial differential equations

Applications of group theory and Liapunov stability to partial differential equation

Bacterial Community Sequences of Submerged Aquatic Vegetation in the Potomac River.

Here, we report results from PCR and sequencing of bacterial 16S rRNA genes from leaf and root surfaces from nine submerged aquatic vegetation (SAV) samples comprising five species. Samples were from four sites along the Potomac River

Jews, Judaism, and Multicultural America

Speaker: Dr. Arnold M. Eisen, Koshland Professor of Jewish Culture and Religion, Stanford University.https://digitalcommons.fairfield.edu/bennettcenter-posters/1208/thumbnail.jp

Genetic and physical mapping of DNA replication origins in Haloferax volcanii

The halophilic archaeon Haloferax volcanii has a multireplicon genome, consisting of a main chromosome, three secondary chromosomes, and a plasmid. Genes for the initiator protein Cdc6/Orc1, which are commonly located adjacent to archaeal origins of DNA replication, are found on all replicons except plasmid pHV2. However, prediction of DNA replication origins in H. volcanii is complicated by the fact that this species has no less than 14 cdc6/orc1 genes. We have used a combination of genetic, biochemical, and bioinformatic approaches to map DNA replication origins in H. volcanii. Five autonomously replicating sequences were found adjacent to cdc6/orc1 genes and replication initiation point mapping was used to confirm that these sequences function as bidirectional DNA replication origins in vivo. Pulsed field gel analyses revealed that cdc6/orc1-associated replication origins are distributed not only on the main chromosome (2.9 Mb) but also on pHV1 (86 kb), pHV3 (442 kb), and pHV4 (690 kb) replicons. Gene inactivation studies indicate that linkage of the initiator gene to the origin is not required for replication initiation, and genetic tests with autonomously replicating plasmids suggest that the origin located on pHV1 and pHV4 may be dominant to the principal chromosomal origin. The replication origins we have identified appear to show a functional hierarchy or differential usage, which might reflect the different replication requirements of their respective chromosomes. We propose that duplication of H. volcanii replication origins was a prerequisite for the multireplicon structure of this genome, and that this might provide a means for chromosome-specific replication control under certain growth conditions. Our observations also suggest that H. volcanii is an ideal organism for studying how replication of four replicons is regulated in the context of the archaeal cell cycle. © 2007 Norais et al

Mice Infected with Low-virulence Strains of Toxoplasma gondii Lose their Innate Aversion to Cat Urine, Even after Extensive Parasite Clearance

Toxoplasma gondii chronic infection in rodent secondary hosts has been reported to lead to a loss of innate, hard-wired fear toward cats, its primary host. However the generality of this response across T. gondii strains and the underlying mechanism for this pathogen mediated behavioral change remain unknown. To begin exploring these questions, we evaluated the effects of infection with two previously uninvestigated isolates from the three major North American clonal lineages of T. gondii, Type III and an attenuated strain of Type I. Using an hour-long open field activity assay optimized for this purpose, we measured mouse aversion toward predator and non-predator urines. We show that loss of innate aversion of cat urine is a general trait caused by infection with any of the three major clonal lineages of parasite. Surprisingly, we found that infection with the attenuated Type I parasite results in sustained loss of aversion at times post infection when neither parasite nor ongoing brain inflammation were detectable. This suggests that T. gondii-mediated interruption of mouse innate aversion toward cat urine may occur during early acute infection in a permanent manner, not requiring persistence of parasitecysts or continuing brain inflammation.Comment: 14 pages, 3 figure

Control Aware Radio Resource Allocation in Low Latency Wireless Control Systems

We consider the problem of allocating radio resources over wireless communication links to control a series of independent wireless control systems. Low-latency transmissions are necessary in enabling time-sensitive control systems to operate over wireless links with high reliability. Achieving fast data rates over wireless links thus comes at the cost of reliability in the form of high packet error rates compared to wired links due to channel noise and interference. However, the effect of the communication link errors on the control system performance depends dynamically on the control system state. We propose a novel control-communication co-design approach to the low-latency resource allocation problem. We incorporate control and channel state information to make scheduling decisions over time on frequency, bandwidth and data rates across the next-generation Wi-Fi based wireless communication links that close the control loops. Control systems that are closer to instability or further from a desired range in a given control cycle are given higher packet delivery rate targets to meet. Rather than a simple priority ranking, we derive precise packet error rate targets for each system needed to satisfy stability targets and make scheduling decisions to meet such targets while reducing total transmission time. The resulting Control-Aware Low Latency Scheduling (CALLS) method is tested in numerous simulation experiments that demonstrate its effectiveness in meeting control-based goals under tight latency constraints relative to control-agnostic scheduling