One-way Signal Research Articles

Regulation of immune responses by inhibitory receptors.

Biological responses, including those occurring during immune responses, must be controlled by signals that turn them on, as well as signals that turn them off. In addition, fine-tuning can be achieved through signals that amplify or downmodulate responses. The complexity in signal transduction pathways that regulate these responses is daunting. Even terminal responses, such as degranulation by effector cells in the immune system, do not follow a simple one-way signaling pathway. The required initial protein tyrosine phosphorylation events are rapidly reversed by dephosphorylation, and the depleted calcium stores are replenished. Unless the effector cell undergoes programmed cell death after activation, it returns to a basal state of activation from where it can be activated again. Negative regulation of effector cell function is sometimes very tight, such that cellular activation is prevented altogether. This type of inhibitory control is an essential feature of natural killer (NK) cells. Unlike cytotoxic T cells that kill target cells upon a recognition event mediated by their antigen-specific receptors, NK cells are triggered to kill target cells by interactions between activating NK receptors and ligands that are expressed fairly ubiquitously on target cells. The specificity in target cell recognition is achieved primarily by inhibitory receptors specific for MHC class I molecules.KeywordsNatural Killer CellInhibitory ReceptorCytoplasmic TailActivate Natural Killer CellMurine Natural Killer CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Dimensions of effective interactive learning with telematics for distance education

Increasingly, telematics is being used for distance education in Australia. Two forms of telematics, audiographics and live interactive television, are described. Audiographics involves two telecommunications links, one which connects computers via modems and a second link which provides an audioconferencing medium through a normal telephone connection. Live interactive television involves the combination of a one-way television signal with a toll-free callback telephone enabling students to communicate directly with the teacher during program transmission. Research and evaluation studies indicate that the interactivity currently implemented via telematics is minimal and that it does not support higher-order cognition among students. In light of our investigations and contemporary cognitive learning theory, a number of dimensions of effective interactive learning with telematics are suggested: (a) collaboration, (b) generative learning, (c) contextual engagement, (d) personal autonomy, and (e) motivation.

Realisation of switched capacitor delay lines and Hilbert transformers

Realisation of switched capacitor delay lines, both for one-way and two-way signal sample propagation are presented. Finite impulse response (FIR) filters can be constructed using tapped delay lines ; particularly, the discussed two-way delay lines are useful for the realisation of filters with antisymmetric impulse responses, such as Hilbert transformers. The switches can be controlled using two-phase clocks.

Excitatory potentials induced by stimulation of the inhibitory axon at the crustacean neuromuscular junction.

Synaptic events in a chloride-deficient condition were studied to elucidate functional aspects of presynaptic inhibitory synapses. The extracellular junctional potentials and nerve terminal potentials were concurrently recorded from a synaptic region. Inhibitory stimulation produced repetitive spikes on the inhibitory nerve terminal and then the excitatory nerve terminal, which resulted in the extracellular excitatory junctional potentials. Excitatory stimulation did not produce repetitive spikes on the inhibitory nerve terminal, indicating one-way signal transmission in this axo-axonal synapse from inhibitory to excitatory axon. The interval required for an inhibitory stimulation to produce the first response in the postsynaptic muscle membrane ranged widely from 10 to 800 msec. When gamma-aminobutyric acid (GABA, 1 times 10-minus 4 M) was added in these experimental conditions, the muscle membrane was transiently depolarized by about 10 mV. The action of GABA mimics that of the neurotransmitter at presynaptic inhibitory synapses. The experimental observations may be well explained by the concept of synapses on synapses, i.e., presynaptic inhibition, where the neurotransmitter may be GABA and chloride ions may be playing essential roles as in the case of postsynaptic inhibition.

Remote sensing of the terrestrial environment with an HF radio high-resolution azimuth and elevation scan system

High-resolution arrays, steerable over a sector in azimuth and elevation, can be used to sense the state of the remote ionosphere and possibly certain characteristics of the sea surface. Direction-of-arrival measurements of one-way signals or backscatter techniques can sense the presence of traveling ionospheric disturbances and determine some of their parameters. Backscatter data can provide information on HF skip distances and ionospheric plasma frequencies at long distances. Spectrum analysis of sea scatter may provide some information on sea state. These uses are illustrated by several examples.

Worldwide Clock Synchronization Using a Synchronous Satellite

An experiment performed in late 1967 is reported which investigated the synchronization of widely separated clocks. One-way VHF timing signals were relayed to remote clocks from a reference clock by means of a transponder on a geostationary satellite. The problem of synchronizing clocks using one-way transmission reduces to the problem of predicting the radio propagation delay. The accuracy of predicting the delay was 10 As or 60 Ms depending on the method used. This technique may offer an alternative to transporting atomic standards to geodetic and spacecraft tracking stations around the world in fulfillment of their clock synchronization requirements.

Systems engineering of personal radio signaling systems

In two other papers Kraus1 and Young2 describe in some detail the operational and equipment features of 35-mc (megacycle) amplitude-modulated systems for providing one-way selective signaling service. This paper covers a number of the problems associated with the planning and evaluation of systems operating in either the 35- or 150-mc range which might be used to provide city-wide coverage. Fig. 1 is a simplified schematic of a signaling system and illustrates three of the major areas to be discussed. These areas are the pocket receiver, the radio transmission path, and finally the central office facilities.

Extrapolation from the Michelson-Morley Experiment

The invariance with motion of the measurement of two-way light signals in the Michelson-Morley experiment is extrapolated to one-way measurements. The time of arrival of signals at a distant point is accepted as indeterminate, in accordance with the before-and-after characterization of Robb; but it is shown that, in spite of this indeterminancy, definite expressions can be obtained for the operations involved in measuring one-way signals. Extension of the same reasoning leads to Lorentz-type transformations expressed in terms of observable rod and clock readings, which include the self-observed velocities of moved clocks used to set the epochs of distant clocks.

The Measurement of the Velocity of Light by Signals Sent in One Direction

The problem of measuring the velocity of light by signals sent in one direction, instead of the usual method, by signals sent out and back, is studied. This requires two clocks, and the necessary steps to set the two clocks are discussed. It is found desirable to distinguish between “velocity” in its elementary and traditional sense, and the “rod-clock-quotient” directly obtained by measurement with rods and clocks experiencing the Fitzgerald-Larmor-Lorentz contractions. The precise formula derived for the one-way measurement of the velocity of light involves two rod-clock-quotients. The use of one-way light signal measurements in the Lorentz transformations and the Special Theory of Relativity is discussed.