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Across a range of motor and cognitive tasks, cortical activity can be accurately described by low-dimensional dynamics unfolding from specific initial conditions on every trial. These “preparatory states” largely determine the subsequent evolution of both neural activity and behavior, and their importance raises questions regarding how they are, or ought to be, set. Here, we formulate motor preparation as optimal anticipatory control of future movements and show that the solution requires a form of internal feedback control of cortical circuit dynamics. In contrast to a simple feedforward strategy, feedback control enables fast movement preparation by selectively controlling the cortical state in the small subspace that matters for the upcoming movement. Feedback but not feedforward control explains the orthogonality between preparatory and movement activity observed in reaching monkeys. We propose a circuit model in which optimal preparatory control is implemented as a thalamo-cortical loop gated by the basal ganglia.

We have performed frequency locking of a dual, forward reverse emitting 3rd order distributed feedback quantum cascade laser (QCL) at 3.5 THz. By using both directions of THz emission in combination with two gas cells and two power detectors, we can for the first time perform frequency stabilization, while monitor the frequency locking quality independently. We also characterize how the use of a less sensitive pyroelectric detector can influence the quality of frequency locking, illustrating experimentally that the sensitivity of the detectors is crucial. Using both directions of THz radiation has a particular advantage for the application of a QCL as a local oscillator, where radiation from one side can be used for frequency/phase stabilization, leaving the other side to be fully utilized as a local oscillator to pump a mixer.

We report a frequency locking experiment of a 3.5 THz third-order distributed feedback quantum cascade laser (QCL) by using a molecular absorption line of methanol (CH[subscript 3]OH) gas. With the help of the absorption line, the frequency noise of the QCL is transformed into measurable amplitude fluctuation. We first present the study of the noise of the THz QCL with the contribution from both the frequency and amplitude domain, by using a NbN superconducting hot-electron bolometer as a power detector. We then present the frequency locking measurement with a lock-in amplifier registering the derivate curve of the absorption line and a proportional-integral-derivative (PID) controller generating the feedback signal. The linewidth of the QCL in the free-running mode was found to be around 900 KHz. This linewidth is reduced to below 17 KHz (full width at half maximum) with a Gaussian-like shape when the control loop is active. Because of the frequency stabilization the noise power spectral density of the QCL shows a reduction of more than 20 dB at frequencies below 30 Hz., China Exchange Programme, Seventh Framework Programme (European Commission) (AMSTAR+ Project of RadioNet), NWO of the Netherlands

We report a set of measurements to demonstrate a new type of surface emitting distributed feedback (DFB) quantum cascade laser (QCL) operated at 3.5 THz as a local oscillator by pumping a superconducting hot-electron bolometer (HEB) mixer. Based on the Bragg gratings incorporated into the waveguide, the second order DFB surface emitting THz QCL shows single mode emission at 3.555 THz, which is only 4 GHz off from the hydroxyl (OH) line. Because of the radiation being emitted from the surface, the far-field beam is much improved, with a divergent far field beam pattern only in one direction. We also notice that in the far field beam pattern, unlike conventional metal-metal waveguide QCLs, there are no interference patterns. All these factors make it possible to fully pump a superconducting NbN HEB mixer at 60 K, and even at 70 K based on the estimated power., China Exchange Programme, Seventh Framework Programme (European Commission) (AMSTAR+ Project of RadioNet), NWO of the Netherlands

Mutations that reduce the function of KCNQ2 channels cause neuronal hyperexcitability, manifested as epileptic seizures and myokymia. These channels are present in nodes of Ranvier in rat brain and nerve and have been proposed to mediate the slow nodal potassium current I(Ks). We have used immunocytochemistry, electrophysiology and pharmacology to test this hypothesis and to determine the contribution of KCNQ channels to nerve excitability in the rat. When myelinated nerve fibres of the sciatic nerve were examined by immunofluorescence microscopy using antibodies against KCNQ2 and KCNQ3, all nodes showed strong immunoreactivity for KCNQ2. The nodes of about half the small and intermediate sized fibres showed labelling for both KCNQ2 and KCNQ3, but nodes of large fibres were labelled by KCNQ2 antibodies only. In voltage-clamp experiments using large myelinated fibres, the selective KCNQ channel blockers XE991 (IC50 = 2.2 microm) and linopirdine (IC50 = 5.5 microm) completely inhibited I(Ks), as did TEA (IC50 = 0.22 mm). The KCNQ channel opener retigabine (10 microm) shifted the activation curve to more negative membrane potentials by -24 mV, thereby increasing I(Ks). In isotonic KCl 50% of I(Ks) was activated at -62 mV. The activation curve shifted to more positive potentials as [K+]o was reduced, so that the pharmacological and biophysical properties of I(Ks) were consistent with those of heterologously expressed homomeric KCNQ2 channels. The ability of XE991 to selectively block I(Ks) was further exploited to study I(Ks) function in vivo. In anaesthetized rats, the excitability of tail motor axons was indicated by the stimulus current required to elicit a 40% of maximal compound muscle action potential. XE991 (2.5 mg kg(-1) i.p.) eliminated all nerve excitability functions previously attributed to I(Ks): accommodation to 100 ms subthreshold depolarizing currents, the post-depolarization undershoot in excitability, and the late subexcitability after a single impulse or short trains of impulses. Due to reduced spike-frequency adaptation after XE991 treatment, 100 ms suprathreshold current injections generated long trains of action potentials. We conclude that the nodal I(Ks) current is mediated by KCNQ channels, which in large fibres of rat sciatic nerve appear to be KCNQ2 homomers.

Performance of an HBT and a Quasi Enhancement Mode PHEMT (QE-PHEMT) unit cell is compared for wireless telephone PA applications. While the HBT has advantages of smaller chip size and single supply with no drain switch operation, the QE-PHEMT has higher efficiency and better low voltage characteristics. PA power control and device design trade-offs for both technologies are also discussed.

We studied skewed adult copepod sex ratios in two ponds in an attempt to understand the ecological causes and evolutionary consequences of this life-history phenomenon. In ponds containing populations of zooplanktivorous sunfish, female copepods suffered higher mortality rates than males, while in ponds lacking these predators, male and female mortality rates were similar. Field and laboratory experiments showed that females, especially those carrying eggs, were more visible than males and that added visibility accounted for higher predation by fish on these individuals. We calculated the cost of carrying eggs in terms of the decreased population growth rate it produces, and then estimated the magnitude of egg mortality necessary to select for the egg-carrying strategy. Eggs not carried would have to suffer at .least 58% mortality for egg carrying to evolve in the presence of selective fish predation. The response of the copepods to these strong selective pressures lies in a third direction, the production of diapausing eggs.

Planktivorous bluegill sunfish (Lepomis macrochirus) are known to consume large prey preferentially. Disagreement exists in the literature over whether this size—selectivity reflects optimal foraging behavior by the fish or relative prey encounter probability as predicted by a model in which apparent size of the prey determines foraging preferences. As bluegills grow larger, their visual resolution increases, and this should affect prey choice under the apparent size model. In laboratory experiments, three sizes or fish were fed identical diets made up of three sizes of Daphnia magna. Large and medium—size fish consumed relatively more large prey than predicted by the apparent size model, whereas the diet of small fish deviated only sightly from the apparent size model. For fish to be more selective than allowed by the apparent size model, they must be able to estimate absolute prey size. To do this requires good vision. Since diet selectivity was highly significantly correlated with the fishes' visual resolution in our experiments, we suggest that visual capability imposes a constraint on the ability of small bluegills to choose prey.

The objective of this study was to investigate the phenomena of subcritical and supercritical spatially varied flow in rectangular expansions such as that in an erosion gully. Based on momentum and continuity principles, equations were developed to predict such flow phenomena. Computations of the water surface profiles for subcritical spatially varied flow were carried out by applying direct step numerical calculations. Because of the presence of standing waves, the method of characteristics was employed in the analytical analysis of the supercritical flow phenomena. Of primary importance in this study is the effect of varying amounts of lateral inflow rates. Other parameters varied during the experimental tests were the slope of the channel and the main channel discharge. Comparison of the analytical and experimental results indicated that for both subcritical and sμpercritical spatially varied flow, water surface profiles can be predicted with good accuracy. Funding information: The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Research Act of 1964.

The objective of this study was to develop a rainfall simulator, which imparts to the laboratory rainfall the more important characteristics of natural rainfall such as intensity, drop spectrum, kinetic energy, and momentum at impact, for using in soil erosion research with better results. In developing this simulator the better features of the basic types of earlier simulators, drip and nozzle, have been incorporated into this single design. The simulator developed in this study consists of a number of individual box modules placed in a rectangular pattern to form a single unit. Each module has a grid of capillary holes with cone shaped exits drilled through the bottom plate. The modules were mounted so that their bottom plates form the ceiling of a pressurized room. This provides a hydrostatic pressure differential between the bottom plate and the water surface in each module, such that water will not leak through the holes during the nonoperating state. When pressure pulses are applied to the water surface in each module, water drops are ejected with an initial velocity so that a terminal velocity corresponding to a natural rain drop can be attained without requiring excessive height of fall. The test results indicated that this simulator provides good · simulation of the natural rainfall erosivity. Funding information: The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Research Act of 1964.

Planktivorous sunfish of various sizes were studied to ascertain whether growth-related changes in the retina are related to the ability to capture small planktonic crustaceans. Behaviorally, the larger fish detected and captured crustaceans that subtended smaller visual angles. Histological examination of the retinas revealed that the distance between cones, measured in minutes of visual angle, decreased as the animals grew, suggesting that the larger retinas could resolve smaller objects. These correlated behavioral and anatomical results suggest that improved visual resolution contributes to improved predation. This finding provides a selective advantage for the continuous retinal growth noted in many fish.