Gait analysis of adult paraplegic rats after spinal cord repair

This study presents a novel detailed method of analysis of rat gait and uses this method to demonstrate recovery of forward locomotion patterns in adult rats made paraplegic by surgical spinal cord transection and subjected to a novel strategy for spinal cord repair. Six normal rats were compared to five animals in which the cord was transected at T8-T9, and a 5-mm segment of the spinal cord removed, and to seven animals in which, following spinal cord transection and removal of a spinal cord segment, multiple intercostal peripheral nerve bridges were implanted, rerouting pathways from white to gray matter in both directions. The implanted area was filled with fibrin glue containing acidic fibroblast growth factor. Details of the repair strategy have been published (H. Cheng, Y. Cao, and L. Olson, 1996, Science 273: 510-513). Gait analysis was carried out 3 and 4 months after surgery and once in the normal animals. Animals were allowed to walk across a runway with a transparent floor. Each test consisted of five trials, and each trial was videorecorded from underneath. Using frame-by-frame playback, individual footprints were then recorded regarding location and order of limb use, as well as step quality (degree of weight bearing, etc.). These data allowed measuring runway transit time, five different measures of step numbers, all possible temporal patterns of limb use, stride length, and base of support. Transected controls remained paralyzed in the hindlimbs with only occasional reflex hindlimb movements without weight bearing. Animals subjected to the full repair procedure were significantly faster than the controls, used their hindlimbs for 25-30% of the movements, and regained several of the specific limb recruitment patterns used by normal rats. Taken together, the gait analysis data demonstrate remarkable recovery of coordinated gait in the repaired animals, which was significantly better than controls for all relevant parameters, while at the same time clearly inferior to normal rats for most of the examined parameters. We conclude that normal rats use a multitude of interchangeable step sequence patterns, and that our spinal cord repair strategy leads to recovery of some of these patterns following complete spinal cord transection. These data suggest functionally relevant neuronal communication across the lesion.     

Evidence of uranium and associated trace element mobilization and retention processes at Oklo (Gabon), a naturally radioactive site

The processes that affect the mobility of uranium and other radionuclides in the environment have been largely studied at both the laboratory and the field scales. The natural reactors found at the Oklo uranium mine in Gabon constitute a unique investigation setting as spontaneous fission reactions occurred two billion years ago. Oklo uraninites contain a large amount of other radionuclides as a result of the fission process. We have investigated the dissolution behavior of four uraninite samples from Oklo as a function of temperature (25 and 60 degrees C) and bicarbonate concentration (2.7-30 mmol/L). We have also investigated the dissolution behavior of minor components of the uraninites (i.e., Nd, Cs, Mo, Yb, and Sb) in relation to the dissolution of uranium. The results of the reported work are in good agreement with the kinetic rate laws derived from other uranium(IV) dioxide studies. Some of the minor components are found to be congruently released from the uraninite phase, while it is postulated that dissolution from segregated phases might affect the final concentrations of some of the rare earth elements, i.e., Nd and Yb. In addition, we have performed dissolution studies at 60 degrees C with two uraninites representative of different geochemical environments at Oklo, to study the uranium dissolution rates as a function of the temperature. This has allowed derivation of apparent activation energies for the bicarbonate-promoted oxidative dissolution of the Oklo uraninites. The dissolution behavior of the minor components of the uraninites at 60 degrees C was found to closely follow the behavior observed at 25 degrees C. This indicates that similar codissolution mechanisms operate in the temperature range studied. The implications for the mobility of uranium and other radionuclides in natural and anthropogenic environments are discussed.     

An Energy-Efficient and Collision-Avoidance MAC Protocol with Pre-scheduling for Wireless Sensor Networks

In this paper, we propose energy efficient MAC protocols for data gathering tree structure. The basic concept of the proposed protocol is that it reduces traffic overloads in low depth nodes by introducing full sleep state for one frame. To maximize network performance, we only control traffic from non-relay nodes which are leaf nodes in the tree. We introduce a new superframe structure for pre-scheduling to alleviate contentions and packet collisions between children nodes. In addition, leaf nodes go into a full sleep mode for one superframe in heavy traffic loads by using control packets, which results in a considerable reduction of energy consumption at low depth nodes. Simulation results show the proposed protocol saves more energy and achieves better packet delivery ratio compared to the DMAC with a moderate increase of a latency performance.     

Optimized Li4Ti5O12 nanoparticles by solvothermal route for Li-ion batteries

Li4Ti5O12 (LTO) nanoparticles were successfully synthesized by solvothermal technique using cost-effective precursors in polyol medium and post-annealed at temperatures of 400, 500, and 600 degrees C. The XRD patterns of the samples were clearly indexed to the spinel shaped Li4Ti5O12 (space group, Fd-3 m). The particle size and morphology of samples were identified using field-emission SEM. The electrochemical performance of solvothermal samples revealed fairly high initial discharge/charge specific capacities in the range 230-235 and 170-190 mAh/g, at 1 C-rate, while that registered for the solid-state sample has been 160 and 150 mAh/g, respectively. Furthermore, among these samples, LTO annealed at 500 degrees C exhibited highly improved rate performances at C-rates as high as 30 and 60 C. This was attributed to the achievement of small particle sizes with high crystallinity in nano-scale dimensions and hence shorter diffusion paths combined with larger contact area at the electrode/electrolyte interface.     

Structural and mechanical characterization of lithium-ion battery electrodes via DEM simulations

Electrode structural stability and mechanical integrity is of major importance regarding not only lithium-ion battery performance but also safety aspects. The goal of this study is to design a simulation procedure to reproduce the microstructural and mechanical properties of such lithium-ion battery electrodes. Taking into consideration the particulate state of these electrodes, a discrete element method (DEM) approach is proposed, which comprises a procedure to reproduce real electrode structures and the application of a proper contact model to capture the bulk mechanics. This is accomplished by considering particle interactions as well as the performance of the binder. Three different electrodes are manufactured with the aim of calibrating and validating the Hertzian-bond contact model. Experimental nanoindentation measurements prove to be in good agreement with the simulation outcome, concluding that the method constitutes a valuable physical and mechanical basis for further applications.     

Heterogeneous pipelined square-root Kalman Filter algorithm for the MMSE-OSIC problem

This paper describes a pipelined parallel algorithm for the MMSE-OSIC decoding procedure proposed in V-BLAST wireless MIMO systems, for heterogeneous networks of processors. It is based on a block version of the square-root Kalman Filter algorithm that was initially devised to solve the RLS problem. It has been parallelized in a pipelined way obtaining a good efficiency and scalability. The optimum load balancing for this parallel algorithm is dynamic, but we derive a static load balancing scheme with good performance.