7,694 research outputs found
Towards a fuller, more nuanced narrative of Chalcolithic and Early Bronze Age Britain 2500-1500 BC
This contribution considers some of the many recent advances in our understanding of Chalcolithic and Bronze Age Britain and uses these to highlight the weak points in our current state of knowledge. Focusing mainly on the period 2500–1500 BC, it concentrates on issues of chronology, human movement, the role of metal and monuments as 'drivers' of action, and the potential offered by current studies of artefact manufacture, use and depositio
Two-D results on human operator perception
The application of multidimensional scaling methodology in human factors engineering is presented. The nonorthogonality of internally perceived task variables is exhibited for first and second order plants with both dependent and independent task variables. Directions of operator preference are shown for actual performance, pilot opinion rating, and subjective measures of fatigue, adaptability, and system recognition. Improvement of performance in second order systems is exhibited by the use of bang-bang feedback information. Dissimilarity measures for system comparison are suggested in order to account for human operator rotations and subjective sense of time
The re-dating of some Scottish specimens by the Oxford Radiocarbon Accelerator Unit (ORAU): results received during 2007
Investigating jet and jet-like artefacts from Prehistoric Scotland: the National Museums Scotland project
Functional Stoichiometry at the Nicotinic Receptor. The Photon Cross Section for Phase 1 Corresponds to Two Bis-Q Molecules per Channel
These experiments examine changes in the agonist-induced conductance
that occur when the agonist-receptor complex is perturbed. Voltage-clamped
Electrophorus electroplaques are exposed to the photoisomerizable agonist
trans-Bis-Q A 1-µs laser flash photoisomerizes some trans-Bis-Q molecules
bound to receptors; because the cis configuration is not an agonist, receptor
channels close within a few hundred microseconds. This effect is called phase 1.
We compare (a) the fraction of channels that close during phase 1 with (b) the
fraction of trans-Bis-Q molecules that undergo trans → cis photoisomerization.
Parameter a is measured as the fractional diminution in voltage-clamp currents
during phase 1. Parameter b is measured by changes in the optical spectra of
Bis-Q solutions caused by flashes . At low flash intensities, a is twice b, which
shows that the channel can be closed by photoisomerizing either of two bound
agonist molecules. Conventional dose-response studies with trans-Bis-Q also give
a Hill coefficient of two. As a partial control for changes in the photochemistry
caused by binding of Bis-Q to receptors, spectral measurements are performed
on the photoisomerizable agonist QBr, covalently bound to solubilized acetylcholine
receptors from Torpedo. The bound and free agonist molecules have the
same photoisomerization properties. These results verify the concept that the
open state of the acetylcholine receptor channel is much more likely to be
associated with the presence of two bound agonist molecules than with a single
such molecule
Conductance increases produced by bath application of cholinergic agonists to Electrophorus electroplaques
When solutions containing agonists are applied to the innervated face of an Electrophorus electroplaque, the membrane's conductance increases. The agonist-induced conductance is increased at more negative membrane potentials. The "instantaneous" current-voltage curve for agonist-induced currents is linear and shows a reversal potential near zero mV; chord conductances, calculated on the basis of this reversal potential, change epsilon-fold for every 62-mV change in potential when the conductance is small. Conductance depends non- linearly on small agonist concentrations; at all potentials, the dose-response curve has a Hill coefficient of 1.45 for decamethonium (Deca) and 1.90 for carbamylcholine (Carb). With agonist concentrations greater than 10^(-4) M Carb or 10^(-5) M Deca, the conductance rises to a peak 0.5-1.5 min after introduction of agonist, then declines with time; this effect resembles the "desensitization" reported for myoneural junctions. Elapid alpha-toxin, tubocurarine, and desensitization reduce the conductance without changing the effects of potential; the apparent dissociation constant for tubocurarine is 2 X 10^(-7) M. By contrast, procaine effects a greater fractional inhibition of the conductance at high negative potentials
- …