Physiological and theoretical analysis of K+ currents controlling discharge in neonatal rat mesencephalic trigeminal neurons

Whole cell voltage- and current-clamp recordings were obtained from mesencephalic trigeminal sensory (Mes 5) neurons identified visually in thin brain stem slices of neonatal rats with the use of infrared video microscopy. These cells exhibited accommodation in spike discharge responses to depolarizing current injection protocols whose duration differed as a function of holding potential (-50 vs. -65 mV). Several spikes were elicited before the membrane response accommodated from -50 mV, whereas from -65 mV only single action potentials were evoked. In response to similar protocols, application of the K+ channel blocker 4-aminopyridine (4-AP) (50 microM to 2 mM) caused sustained repetitive spiking whereas tetraethylammonium (TEA) (10-30 mM) did not cause repetitive spiking. In voltage clamp, 4-AP application (100 microM) revealed a sustained outward current (I4-AP) that was active between -60 and -30 mV. I4-AP was responsible for suppressing sustained repetitive spiking behavior, producing accommodation under normal circumstances. TEA application in voltage clamp revealed a sustained outward current evoked positive to -40 mV. Two transient outward currents (TOCs) were identified by prepulse protocols typically used to characterize A-type currents: a 4-AP-insensitive fast TOC, and a slow TOC (ITOC-S) sensitive to 4-AP (> 500 microM). A Ca(2+)-dependent outward current that activated positive to -30 mV was also characterized. A mathematical model of a Mes 5 neuron was assembled from our voltage-clamp records to simulate the dynamic interaction of outward currents during membrane excitation. We conclude that in Mes 5 neurons, the 4-AP-sensitive currents ITOC-S and I4-AP determine the duration of spike trains. In particular, the noninactivating I4-AP determines whether cells exhibit sustained repetitive discharge or accommodate in response to depolarizing current. Neurotransmitter modulation of this current or modulation of the resting membrane potential could modify the output properties of Mes 5 neurons, and therefore the properties of these currents must be incorporated into our current understanding of how these cells contribute to shaping oral-motor pattern generation.     

Cellulose acetate as a selective sorbent for limonin in orange juice

Cellulose acetate as flake or powder is an efficient and selective sorbent for removing the bitter principle limonin from orange juice. Treatment of orange juice serum with powder (10 g/litre) removed 44–70% of the limonin content in less than an hour, at the same time removing relatively negligible amounts of hesperidin and ascorbic acid. Similar amounts of limonin could be removed by agitating the whole juice with cellulose acetate flakes held in open mesh bags which allowed contact between the enclosed flakes and the juice. Other materials, including related carbohydrate derivatives and polymers, were tested but only cellulose acetate butyrate shared the unusual sorptive properties of cellulose acetate.     

Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes

Ostracode magnesium/calcium (Mg/Ca)-based bottom-water temperatures were combined with benthic foraminiferal oxygen isotopes in order to quantify the oxygen isotopic composition of seawater, and estimate continental ice volume and sea-level variability during the Mid-Pliocene warm period, ca 3.3-3.0Ma. Results indicate that, following a low stand of approximately 65m below present at marine isotope stage (MIS) M2 (ca 3.3Ma), sea level generally fluctuated by 20-30m above and below a mean value similar to present-day sea level. In addition to the low-stand event at MIS M2, significant low stands occurred at MIS KM2 (-40 m), G22 (-40m) and G16 (-60m). Six high stands of +10m or more above present day were also observed; four events (+10, +25,+15 and +30 m) from MIS M1 to KM3, a high stand of +15m at MIS K1, and a high stand of +25m at MIS G17. These results indicate that continental ice volume varied significantly during the Mid-Pliocene warm period and that at times there were considerable reductions of Antarctic ice.     

Performance-based design in earthquake engineering: a multi-disciplinary review

This paper reviews the contributions of research towards the development of the methodologies associated with Performance-Based Seismic Engineering (PBSE). Research undertaken in various related disciplines is reviewed, under the broad section headings of (i) Engineering Seismology and Geology (Seismic Activity Modelling), (ii) Engineering Seismology (Seismic Hazard Modelling), (iii) Soil Dynamics, (iv) System Dynamics, and (v) Mechanics of Materials (Concrete used as example). The sequence of the discussion is consistent with a typical seismic assessment procedure, which commences with seismic activity modelling in the ‘upstream’ end of the procedure and finishes with consideration of structural mechanics behaviour at the ‘downstream’ end. Each section provides an outline of historical research and development, leading to a review of the state-of-the-art approaches. Particular emphasis is given to the inter-linking of the disciplines, and the paper refers to such links as ‘Nodal Points’. An example of a nodal point is the definition of probabilistic seismic hazard coefficients that are used to define seismic hazard in terms of elastic response spectra, for example the response spectral accelerations at key periods of 0.3 and 1.0 s. Each of the Nodal Points associated with the various disciplines has been critically reviewed, and shortcomings have been identified. For example, the inability of a probabilistic approach to fully represent an earthquake event as a physical process is highlighted. Also, the importance of putting emphasis in future research on determining the Maximum Credible (or Considered) Earthquake, MCE, is emphasised.

The paper brings to light the fact that, although significant achievements have been made in each of the related disciplines and in the connection of the Nodal Points, there has been relatively little change in substance at the Nodal Points themselves. An important outcome of this multi-disciplinary review is the identification of some key limitations in current procedures. The source of these limitations was traced upstream, and thence to the Nodal Points that provide the inter-disciplinary links. This process has been referred to herein as Upstream Feedback. A review of the problems at these links sows the seeds for further development, which would not have been possible had all the recent contributions been confined within the individual disciplines. Such an Upstream Feedback process, enabling improvements to the multi-discipinary links, would be instrumental in enhancing the overall effectiveness of PBSE in the future.     

Characterization of Impact Damage in Ultra-High Performance Concrete Using Spatially Correlated Nanoindentation/SEM/EDX

Little work has been done to study the fundamental material behaviors and failure mechanisms of cement-based materials including ordinary Portland cement concrete and ultra-high performance concretes (UHPCs) under high strain impact and penetration loads at lower length scales. These high strain rate loadings have many possible effects on UHPCs at the microscale and nanoscale, including alterations in the hydration state and bonding present in phases such as calcium silicate hydrate, in addition to fracture and debonding. In this work, the possible chemical and physical changes in UHPCs subjected to high strain rate impact and penetration loads were investigated using a novel technique wherein nanoindentation measurements were spatially correlated with images using scanning electron microscopy and chemical composition using energy dispersive x-ray microanalysis. Results indicate that impact degrades both the elastic modulus and indentation hardness of UHPCs, and in particular hydrated phases, with damage likely occurring due to microfracturing and debonding.     

Quantitative Physiological Assessment of Stress Via Altered Immune Functioning Following Interaction With Differing Automotive Interface Technologies

Technology can enhance or diminish a user's psycho-physiological stress level; the ability to quantify these responses can help evaluate and refine design. The capability of drivers to accomplish basic tasks utilizing differing sensory modalities while maintaining lane discipline within a computer-simulated environment was assessed. Fifteen healthy subjects provided capillary blood samples before and after using three human–machine interface designs—touch-screen, voice control, and multimodal. Using a chemiluminescent technique termed Leukocyte Coping Capacity, the ability of leukocytes to produce reactive oxygen species in vitro was assessed. Significant poststressor changes in leukocyte activity of varying magnitude were observed following the use of all interfaces; with the multimodal interface provoking the most pronounced response and voice control the least. Although still requiring further research, the results support the proposition for using immune responsiveness as a means for quantifying psychological stress during assessment of ergonomic design and psycho-physiological and social interaction.     

LOW CYCLE FATIGUE LIVES OF NOTCHED COMPONENTS

Abstract— In low cycle fatigue situations, the plastic behaviour of the material at the root of stress concentrators is of prime importance in determining the cyclic life. However, simple procedures such as Neuber's rule do not adequately describe the development of plastic behaviour at a notch root, while the expense of a finite element analysis is not justified in many instances. This paper describes a simple, approximate numerical method of calculating plastic notch stresses and strains that would be of use in such situations. The usefulness of the technique is demonstrated by comparing low cycle fatigue lives predicted from notch plastic strains with those determined by fatigue testing of smooth specimens subjected to similar plastic strain ranges.