Narrow-band System Research Articles

The theoretical study of a new multi-bunch damping mechanism

The most efficient method to damp multi-bunch oscillations in a storage ring is to install an active feedback loop. However, the technical problem of such a device is connected with the high bandwidth which is defined by the inverse of the time of flight between adjacent bunches. It can be shown theoretically that the bandwidth can be reduced drastically if a narrow-band feedback system is combined with frequency splitting between bunches. The bandwidth of such a damper system is then defined only by the damping rate needed. This seems to be reasonable from a pure mathematical point of view.

The application of packet switching techniques to combat net radio

The narrow-band Packet Radio system which is the subject of this paper is a highly flexible and survivable data communications system for the Forward Area tactical environment achieved by applying packet switching techniques to Army Combat Net Radio. The User requirements driving this development are outlined. It is important that this system is not viewed as being in competition with other Packet Radio systems, but as one system or building block in an integrated electronic battlefield, hence the emphasis on internetworking. Important design considerations such as survivabifity and the abifity to operate with random network topologies are discussed. A detailed description of the algorithms for Channel Access, Routing, and Network Control which were developed using finite-state-machine simulation techniques is then given followed by a summary of the simulator performance predictions for various scenarios. Packet Radio is a synergism of signal processing and communications protocols implemented on real-time systems. The signal processing requirements and architecture adopted for signaling in the VHF environment are described in the context of the hardware for a prototype network. Early experience resulting from trials and demonstrations with this network are used to point to refinements in the next iteration of system design.

Bipolaronic superconductivity: Thermodynamics, magnetic properties, and possibility of existence in real substances.

We examine systems where narrow-band electrons strongly couple to the lattice, resulting in the formation of locally bound pairs of small polarons, so-called bipolarons. Such systems present a hard-core charged Bose gas on a lattice. We study the strong dependence of the mass of these bosons and the interaction among themselves as a function of the characteristic phonon frequency. The conditions under which a phenomenological negative-U Hubbard model is applicable to such systems are established. We derive the phase diagram and excitation spectrum, fully taking fluctuations into account. It turns out that quantum fluctuations stabilize the homogeneous superconducting phase and suppress charge order. The specific heat in the superconducting phase shows a power-law behavior: ${C}_{s}$\ensuremath{\sim}${T}^{\ensuremath{\alpha}}$, with (3/2)\ensuremath{\le}\ensuremath{\alpha}\ensuremath{\le}3, depending on the temperature. The specific heat in the normal phase for such heavy bosons on a lattice shows linear T dependence at low temperature and a ${T}^{\mathrm{\ensuremath{-}}2}$ behavior for high temperature. We demonstrate that the specific heats in the normal state for narrow-band bosons and fermions on a lattice are practically identical. The spin susceptibility of triplet-bipolarons shows Curie behavior at high temperature, but differs qualitatively from the Pauli susceptibility of narrow-band electrons at low temperature. We examine the electrodynamics of the superconducting phase. The equivalent of the Ginzburg-Landau theory for the narrow-band strong-coupling electron-lattice system is derived; this represents an equation of the order parameters of the charged interacting Bose gas which determines the upper critical field and coherence length, which are strongly dependent on the scattering mechanism for the bosons. In the case of impurity scattering they show unusual temperature dependence: ${d}^{2}$${H}_{c2}$/${\mathrm{dT}}^{2}$>0. The possible application of our picture of heavy bosons to the description of certain A15 compounds, Chevrel phases, heavy-fermion systems, and ${\mathrm{BaBi}}_{\mathrm{x}}$${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{O}}_{3}$ is discussed.

Magnetic ground state and the mixed valence in doubly degenerate narrow-band system

Abstract We analyze magnetic and mixed-valent states of electrons composing a band and an atomic level which arise from the removal of strong hybridization between the two components of a degenerate band. We obtain both continuous and discontinuous onsets of ferromagnetic ordering. A brief discussion of results for transition-metal disulphides is given.

A narrow-band sing-around ultrasonic velocity measurement system

Conventional sing-around systems for the measurement of ultrasonic velocity use short (broad-band) pulses. A novel sing-around system is reported in which the transmitted pulse has a narrow bandwidth (quasi-continuous wave), the triggering of the succeeding pulse being obtained from a preselected zero-crossing. The advantages of the technique stem from the avoidance of the problems involved in the conventional use of short (broad-band) pulses, which are particularly acute in highly dispersive media. Measurements on distilled water using the present system are reported, and agree well with those obtained using a conventional leading-edge detector system.

TIO BAND STRENGTHS IN METAL-RICH GLOBULAR CLUSTERS. IV. THE SOLAR NEIGHBORHOOD SEQUENCE.

ABSTRACT TiO band strengths and near infrared color indices have been measured in a sample of nearby late-type giants for the purpose of comparison with observations in metal-rich globular clusters. Transformations to the Wing narrow-band system are determined.

Developing the next phase in NASAs satellite communications program

NASAs early efforts in satellite communications development brought confidence in space technology use for improved telecommunications. New, worldwide satellite communications systems have resulted, and are now on a commercial, self-sustaining operational basis. Since 1973, NASA has conducted hundreds of user experiments and demonstrated newer technology using ATS-1, -3, -6 and CTS. Now, projections show that the commercial demand will continue to increase, soon exceeding the current technology's capacity. As a result, U.S. Space Policy affirmed in 1978 that NASA should embark again on a research and development program for satellite communications with specific, characterized goals. The resulting plan's elements include 30 20 GHz Ka-band technology, extending the current work in advanced multi-beam antennas; a narrowband system and technology study that could lead to mobile and transportable communications developments; and studies of future uses of technology in communications. The program plan and its evolution are described, followed by a report of current progress and future expectations.

Beam profiling using correlation systems

Two techniques are described in which ultrasound beam profiles are measured by means of the radiation reflected from a hemispherical target whose effective reflecting diameter is less than a wavelength. One method employs a modified directional Doppler system to measure narrow-band beam patterns. The other method is a modification of a random signal flaw detection system and is used to measure broad-band beam patterns. Highly sensitive correlation detectors are used in both techniques to improve the signal-to-noise ratio of the received echoes. As the target is scanned across the beam, in a plane approximately parallel to the aperture, the phase of the correlation reference signal must be adjusted to compensate for changes in time-of-flight of the received echo. The broad-band beam profiling technique uses a manual phase compensation technique. The narrow-band system employs a phase quadrature method to achieve the required phase compensation.

On the Dielectric Function of the Hubbard Model

AbstractThe dielectric function of the Hubbard model is discussed in the strong correlation limit. It is shown that there are in general two zero points of the real part of the dielectric function outside the absorption region which correspond to different types of charge density oscillations. In the zero frequency limit an expression for the dielectric function is derived which allows the explanation of the screening of the potential of a donor ion in a narrow energy band system.

Communications: Single-sideband transmission for land mobile radio: From seven to ten times as many channels could be made available in existing VHF and UHF bands

It is suggested that from seven to ten times as many channels could be made available in existing VHF and UHF bands. FM, AM, and SSB modulation techniques combined with syllabic amplitude and frequency compandors are compared. In the 15- to 30-dB signal-to-noise ratios-the amplitude-compandored SSB system and the amplitude- and frequency-compandored SSB system provide the same or better quality reception than FM systems that have comparable transmitter power. Three to five channels of the narrow-band system can be used between the channels of the 25-kHz spaced FM channels without unacceptable interference on either system. Ten narrow-band channels can operate in the 25-kHz bandwidth if there are no FM channels present.

Generation of single ultrashort CO_2 laser pulses in a Fabry–Perot interferometer

In a manner analogous to optical free-induction decay, we have generated ultrashort (<100 psec) intense infrared optical pulses by reflecting an abruptly terminated CO(2) laser pulse from an appropriately adjusted Fabry-Perot interferometer. Because a suitable resonantly absorbing material is not required, the scheme is applicable to any intense narrow-band laser system.

Tandem Connections of Wideband and Narrowband Speech Communications Systems: Part 1-Narrowband-to-Wideband Link

The performance of a tandem connection of narrowband and wideband speech communication systems is evaluated. Specifically, the narrowband system consists of a conventional linear Predictive Coding (lpc) vocoder operating at a bit-rate of 2.4 kb/s and the wideband system consists of a Continuously Variable Slope Delta modulator cvsd operating at a bit rate of 16 kb/s. In Part 1 of this paper the properties of the narrowband-to-wideband link are investigated and in Part 2 the properties of the wideband-to-narrowband link are investigated. In part 1 the snr (signal-to-quantizing noise ratio) of the cvsd coder is analyzed over a 50-dB variation of the input signal levels and for a variety of source excitations for the lpc synthesizer. It is shown that snr improvements in the cvsd coder of 2 to 2.5 dB are possible in the slope overload region of the coder by modifying the source excitation of the lpc synthesizer and by preprocessing the input signal to the coder with an allpass filter. Both methods aid in reducing the peak factor (peak-to-rms level) of the input speech to the coder. Subjectively, however, only slight improvements in quality, if any, were observed with these modifications.

A tunable, frequency-doubled, continuous-wave dye laser using ADA

A tunable, continuous-wave, frequency-doubled, rhodamine 6G dye laser has been developed using an ADA crystal placed in an astigmatic and coma compensated cavity. Generated UV powers of the order of 30mW cw in a single direction in gaussian form over the range 292–302 nm have been obtained by temperature phase matching, and with a 4.5 W pump. Power output is affected by thermal phase mismatching, and is ultimately limited by thermal lensing. Two scanning systems have been developed; a broadband arrangement of linewidth 0.02 nm continuously tunable over a range of 2 nm, and a narrowband system of linewidth 0.002 nm continuously tunable over a range of 1 nm. The laser has been used to detect the Rydberg states of Rb up to a principal quantum of n = 74.

Analysis of the performance of a tandem connection of a 2.4-kB/sec LPC vocoder to a 16-kB/sec CVSD coder

The performance of a tandem connection of narrow-band and wide-band speech communication systems is evaluated. Specifically, the narrow-band system consists of a conventional LPC vocoder operating at a bit rate of 2.4 Kb/sec and the wideband system consists of a CVSD (continuously variable slope delta modulator) operating at a bit rate of 16 Kb/sec. This paper describes the properties of the narrowband to wideband link. The SNR (signal-to-quantizing noise ratio) of the CVSD coder is analyzed over a 50-dB variation of the input signal levels and for a variety of source excitations for the LPC synthesizer. It is shown that SNR improvements in the CVSD coder of 2–2.5 dB are possible in the slope overload region of the coder by modifying the source excitation of the LPC synthesizer and by preprocessing the input signal to the coder with an allpass filter. Both methods aid in reducing the peak factor (peak to rms level) of the input speech to the coder. Subjectively, however, only slight improvements in quality, if any, were observed with these modifications. The weakest link in terms of quality in the tandem connection appears to be that of the CVSD coder.

A Practical Narrow-Band Television System: Sampledot

A new narrow-band TV system called Sampledot, which produces a live picture with motion and sharpness that is a satisfactory replica of conventional TV, is described. Bandwidth compression ratios of 10:1 have been demonstrated with relatively simple electronics. Higher compression ratios are projected using the technique with a dynamic display memory or storage. The system is compatible with NTSC or EIA video cameras and monitors. Sampledot works on the principle of gating the line-scan video signal raster with a pseudorandom (PR) dot-sample matrix. About 3 percent, or less, of the picture is sent every fast scan field instead of the usual 50 percent. At the receiving end, the monitor raster is gated in step with the PR matrix. The natural integration effects of the eye-brain characteristics plus optional display memory, the large redundancy of TV video, and the high degree of correlation between adjacent TV pixels are exploited in the Sampledot technique.

Doppler tracking performance

The performance of a narrow-band passive acoustic tracking system utilizing Doppler frequency shift depends upon both the sensor field geometry and the accuracy with which frequency shifts may be estimated. In general, there exists a relationship between these two factors independent of the implementation of an actual processing system. The characteristics of this relationship are presented in this paper with specific performance bounds being obtained for typical sensor field geometries. It is shown that for frequency estimation accuracies obtainable with currently available hardware, and within the constraints of available signal-to-noise ratio, sensor field geometry becomes the major determinant of tracking performance.

Amplified spontaneous emission and signal amplification in dye-laser systems

Transversely pumped dye-laser systems are investigated theoretically and experimentally. A set of coupled rate equations for the excited-state population densities and for the photon fluxes in both directions, at all wavelengths, is presented. Both the temporal and spatial dependence of these quantities are accounted for. The equations are solved numerically for a variety of practical situations, and analytical approximations for some limiting cases are discussed. The results describe the dependence of the amplified-spontaneous-emission (ASE) output flux on pumping rate, the spectral narrowing process, and the effects of gain saturation. It is found that under practical laboratory conditions the gain of such dye systems saturates rapidly. Consequently, at high pumping rates the output varies linearly with pump intensity, and the conversion efficiency from pump to ASE photons approaches unity. The performance of dyedaser amplifiers is described by the same set of equations, and the gain characteristics of such systems are analyzed as a function of input signal intensity and pumping rate. The theoretical calculations are compared with the results of a set of experiments, and good agreement is found. The operation characteristics of a dye-laser amplifier are evaluated and utilized in the design of a narrow-band oscillator-amplifier system.

Practical feed network design for antenna arrays

Computational procedures have recently been developed which accurately determine the excitation (including mutual coupling effects) at each element of a closely spaced array enabling it to perform in some desired manner. A procedure for designing a transmission-line feed network capable of realizing these required excitations is described. The result is a narrow-band feed system composed simply of a transmission line together with a small number of stubs. A comparison between theoretical and experimental results is given.

Narrow Band Photometry of Supergiant Stars

At the National Astronomical Observatory in San Pedro Mártir, B. C. (Mexico), we have performed photoelectric photometry for 31 stars in a narrow-band system. The system allows the measurements of total absorptions of neutral oxygen at 7774 Å through three interference filters (20–25 Å half-width), one for the OI lines and two for the continuum.The preliminary results are very encouraging: Supergiant stars, ranging in spectrum from the later subdivisions of type B to early G, can be clearly separated from other luminosity classes. The total absorptions depend strongly on the stellar luminosity and, to a lesser degree on the effective temperature (spectral type) of the star. The system may be improved by using narrower filters and detectors with a higher quantum efficiency, already in existence.

Narrow-band systems and Gaussianity

The approach to Gaussianity of the output <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y(t)</tex> of a narrow-band system <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h(t)</tex> is investigated. It is assumed that the input <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> is an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</tex> -dependent process, in the sense that the random variables <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t + u)</tex> are independent for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u &gt; a</tex> . With <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F(y)</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G(y)</tex> the distribution functions of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y(t)</tex> and of a suitable normal process, a realistic bound <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</tex> on the difference <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F(y) -- G(y)</tex> is determined, and it is shown that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B \rightarrow 0</tex> as the bandwidth <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\omega_o</tex> of the system tends to zero. In the special case of the shot noise process \begin{equation} y(t) = \sum_i h(t - t_i) \end{equation} it is shown that \begin{equation} \mid F(y) - G(y) \mid < (\omega_o/\lambda) \frac{1}{2} \end{equation} where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda_i</tex> is the average density of the Poisson points <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t_i</tex> .