Gain control in reflex pathways

Summary form only given. A series of experiments was undertaken to determine the gain of the stretch reflex in decerebrate cats. Stretches are applied through a servo-controlled motor that receives length and velocity feedback which are adjusted so that it behaves like a spring of a particular stiffness. As the stiffness decreases the gain of the reflex increases until the stiffness is made much less than the intrinsic muscle stiffness. Under these conditions small brief pulses can elicit shortening of 1 mm or more and reflex forces that are larger than the force produced by the stretch itself. This suggests that the gain in the reflex is 1 or more at low frequencies. It is concluded that muscle control systems are adaptive and time-varying to accomplish the various tasks required by the organism. Although under some conditions the reflex gain is on the order of one, measurement of gain is compounded by a number of nonlinearities, and the value of these nonlinearities in various tasks remains to be determined     

Self-representation of suicidal adolescents

This study focused on the self-representations of suicidal adolescent. Twenty-six Israeli suicidal inpatients, 24 nonsuicidal inpatients, and 24 control participants completed scales on suicidal tendencies, the hedonic value of self-representations, the complexity (differentiation, integration) of these self-representations, and the discrepancies among self domains (actual, ideal, ought). Suicidal adolescents showed more negative self-representations, a less differentiated and less integrated organization of self-attributes, and more discrepancies between the 3 assessed domains of the self than did control participants. In addition, compared with psychiatric nonsuicidal participants, suicidal adolescents showed a less complex organization of self-attributes and a higher discrepancy between ideal self and ought self. Results were discussed in terms of the vulnerable self of suicidal adolescents, characterized by uneven processing of positive and negative information, confusion, and simplicity.     

How Non-native Species in Lake Erie Influence Trophic Transfer of Mercury and Lead to Top Predators

Lake Erie's food web has been dramatically modified by exotic species. Both exotic dreissenid mussels and the round goby Neogobius melanastomus have shifted the food web from a pelagicbased to a benthic-based one, potentially creating a new pathway for contaminant transfer to top predators. Before the invasion of round gobies, few predators of dreissenids occurred in Lake Erie, allowing contaminants to be confined to these benthic organisms. The invasion of the round goby has produced a new pathway through which these contaminants can enter the food web. To characterize heavy-metal transfer through this new food web and to assess risk to humans, water, surficial sediment, dreissenid, round goby, and smallmouth bass Micropterus dolomieui samples were collected at three sites during summers, 2002 and 2003, and analyzed for total lead (Pb), total mercury (Hg), and methyl mercury (MeHg). In addition, we compared smallmouth bass Pb and Hg concentrations to those measured in 1993/1994, before round gobies were prevalent. Pb biodiminished and MeHg biomagnified through the food web to smallmouth bass; patterns were similar among our three sites. Total Pb concentrations in smallmouth bass were higher before the incorporation of round gobies into their diet. We attributed this decline to changes in food web structure, changes in contaminant burdens in prey, or declines in sediment Pb concentrations in Lake Erie. By comparison, Hg concentrations in smallmouth bass changed little, before and after the round goby invasion, possibly due to a shift in diet that increased growth. Despite a decline in sediment Hg concentrations in Lake Erie, smallmouth bass continued to accumulate Hg at historical rates possibly because of their high consumption rates of benthivorous round gobies. As smallmouth bass continue to consume round gobies during their lives, their Hg concentrations may well continue to increase, potentially increasing the risk of Hg contamination to humans.     

Fast Consecutive Intramolecular Processes Involving Protein and Fe(III) in Ferri-Cytochrome-c in Aqueous Solution

The reaction of H atoms (produced by nanosecond pulse radiolysis) with ferri-cytochrome-c in aqueous solution results in the second order formation of an absorption spectrum due to the addition of H atoms to the enzyme protein. This spectrum is not specific to the iron moiety. The rate constant of the addition is 1×10¹⁰M^?1 sec^?1. This is followed by two first order intramolecular processes with specific rates of ～ 1×10⁵ sec^?1 and ～ 2×10⁴ sec^?1. In these processes, specific spectra related to the α and β bands of ferro-cytochrome-c appear. The results are interpreted to show reduction equivalent transfer through the protein to the iron moiety.     

Über die Herstellung von α-Sulfofettsäureestern

Preparation of Esters of α-Sulfo-Fatty Acids A process for the continuous α-sulfonation of saturated fatty acid esters with SO₃ was worked out and a special bleaching process was developed for these products. The conversion, i. e. the degree of sulfonation is of the order of 95–99%. Solvents, further processing steps or purification operations for the separation of by-products are not required.     

Influence of amorphous silica on the hydration of tricalcium aluminate

Amorphous silica influences tricalcium aluminate (C₃A) hydration both in pastes and in suspensions. Two heat peaks are found by isothermal calorimetry during the paste hydration of C₃A. The addition of amorphous silica causes the second heat peak to shift towards shorter reaction times and become more pronounced. In suspensions, the change in ion concentration in the water phase is not influenced by the presence of amorphous silica except that the change in concentration occurs more quickly. Quantitative X-ray analysis shows that more 3CaO.Al₂O₃.6H₂O is present in suspensions containing amorphous silica than in silica-free suspensions at equal hydration times.     

Zur oligomerenbildung bei der thermischen polymerisation von styrol

It is shown that in thermal polymerization of styrene four dimers and six trimers are formed by parallel occurring oligomerization reactions. With increasing temperature the rate of oligomerization increases more rapidly than the rate of polymerization. The relativ yields of the different oligomers depend on temperature, too.     

Sensory nerve recording for closed-loop control to restore motorfunctions

A method is developed for using neural recordings to control functional electrical stimulation (FES) to nerves and muscles. Experiments were done in chronic cats with a goal of designing a rule-based controller to generate rhythmic movements of the ankle joint during treadmill locomotion. Neural signals from the tibial and superficial peroneal nerves were recorded with cuff electrodes and processed simultaneously with muscular signals from ankle flexors and extensors in the cat's hind limb. Cuff electrodes are an effective method for long-term chronic recording in peripheral nerves without causing discomfort or damage to the nerve. For real-time operation the authors designed a low-noise amplifier with a blanking circuit to minimize stimulation artifacts. They used threshold detection to design a simple rule-based control and compared its output to the pattern determined using adaptive neural networks. Both the threshold detection and adaptive networks are robust enough to accommodate the variability in neural recordings. The adaptive logic network used for this study is effective in mapping transfer functions and therefore applicable for determination of gait invariants to be used for closed loop control in an FES system. Simple rule-bases will probably be chosen for initial applications to human patients. However, more complex FES applications require more complex rule-bases and better mapping of continuous neural recordings and muscular activity. Adaptive neural networks have promise for these more complex applications