Null Region Research Articles

Congenital Nystagmus Surgery

Nystagmus intensities at various gaze angles were studied both preoperatively and postoperatively, using accurate ocular motility recordings, in three cases of congenital nystagmus. In addition to shifting the nystagmus null, the surgery broadened the null region and resulted in an overall reduction in nystagmus intensity at all gaze angles. Surgical rotation also resulted in improved visual acuity in all cases. The postoperative acuity at 0 degrees was better than the preoperative acuity at both 0 degrees and the patient's preferred gaze angle (ie, the preoperative null angle). This was not only for the two patients who showed an improved preoperative acuity with their head turn but also for the patient whose preoperative acuity did not substantially improve with her preferred head turn. Eye movement recordings have made it possible to accurately determine the amount of surgery required and to predict acuity increases even when undetectable during the preoperative clinical examination.

The ultraviolet variations of IOTA Cassiopeiae

We observed the Ap variable star Cas with the photometers on OAO-2 in the spectral range AAl430-4250. The ultraviolet light curves show a double wave with primary minimum and maximum at 4) = 0.00 and 0.35, respectively. Secondary minimum light is at 4) = 0.65 with secondary maximum at 4) = 0.8,5. The light curves longward of A31 50 vary in opposition to those shortward of this "null region.' Ground-based coude' spectra show that the Fe ii and Cr ii line strengths have a double-wave variation, with maximum strength occurring at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due t? photoionization and line blanketing by these metals may cause the observed photometric variations. We have also constructed an oblique-rotator model which shows iron and chromium lying in a great-circle band rather than in circular spots. These elements have been observed to lie in bands along the magnetic equator in several other Ap stars such as a2 CVn, HD 173650, 108 Aqr, and possibly HD 98088. We predict maximum field strengths occurring at minimum strength of the iron and chromium lines: 4) = 0.35 and 4) = 0.85. Subject headings: opacities - stars: individual - stars: peculiar A - ultraviolet: general

Analysis of a case of periodic alternating nystagmus.

A patient is described in whom there was periodic deviation of the eyes in darkness associated with alternating nystagmus. An exactly similar situation occurs in normal man subjected to a pendular stimulus. It is proposed that in this patient there was alternating activity of the vestibular nuclei on either side of the brain-stem as a result of a removal of cerebellar inhibition, and that this caused periodic shifts in the null region of Daroff and Dell'Osso.

The Ultraviolet Variations of ι Cas

SummaryThe Ap variable star ι Cas was observed with the photometers on OAO-2 covering the spectral range λλ 1430-4250. The ultraviolet light curves show a double wave with primary minimum and maximum at ϕ = 0.00 and 0.35, respectively. Secondary minimum light is at ϕ = 0.65 with secondary maximum at ϕ = 0.85. The light curves longward of λ3150 vary in opposition to those shortward of this “null region”.Ground-based coude spectra show that the Fe II and Cr II line strengths have a double-wave variation such that maximum strength occurs at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due to photoionization and line blanketing by these metals may cause the observed photometric variations.We have also constructed an oblique-rotator model which shows iron and chromium lying in a great circle band rather than in circular spots. These elements have been observed to lie in bands along the magnetic equator in several other Ap stars such as α2CVn, HD 173650, and 108 Aqr. Thus, we predict that the inclination of the magnetic dipole field with respect to the axis of rotation is about 84°.

FIXATION CHARACTERISTICS IN HEREDITARY CONGENITAL NYSTAGMUS

Binocular eye movement recordings and laser-target retinal cinematography were employed to identify a fixation bias in a case of hereditary congenital nystagmus. The oscillations of each eye varied with gaze angle and were, in general, unequal over a ± 30° range of gaze. Although the nystagmus frequency was also gaze-angle dependent, it was equal in both eyes. In the null region both nystagmus amplitude and frequency were minimal and equal for the two eyes. The lateral fixation bias was found to occasionally shift in direction simultaneously in both eyes; this preserved retinal correspondency and, in conjunction with the nulling effect of convergence and proper gaze angle, contributed to increased visual acuity. These findings support and further clarify the mechanisms by which the previously described prism lenses dramatically increased visual acuity. The attempt to fixate was identified as the adequate stimulus for the nystagmus.

Radiation from a circularly polarized antenna through the ionized wake of a Mars-entry capsule

The effects of the ionized wake-of a Mars-entry capsule on radiation from a circularly polarized antenna operating at 400 and 2295 MHz are studied. The circularly polarized antenna is represented by a turnstile antenna <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/4</tex> above a ground plane, while the ionized wake is approximated by a cylindrically stratified plasma consisting of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> -plasma regions. Integral expressions for the fields are obtained for the antenna located in the wake and are evaluated using saddle-point integration to yield the radiation patterns. Computed patterns for the two simplest configurations <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N = 1</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N = 2</tex> are presented. The radiation patterns for both near- and far-wake electron-density profiles develop a conical null region whose extent is proportional to the peak electron density in the wake. For the near-wake electron-density profile, sharp peaks which are attributable to leaky-wave radiation, appear within the null region of the patterns. The effect of the conical null region in the patterns is to prolong blackout time for communication cone angles that lie within the null region. There are no serious depolarization effects in the nonnull region and satisfactory communications can be carried out.

Gas-Phase Complexes in Hydrogen Chloride

The null gap region of the fundamental band of HCl has been studied in the case where argon and xenon are used as perturbing gases. The experiments were performed using an absorption cell of 150 cm length. The absorption cell could be varied in temperature from room temperature to 195°K. The complex features previously observed in the spectrum at room temperature were greatly enhanced in intensity at the lowest temperature. The absorption spectrum of pure HCl gas was found to show strong evidence for dimer formation, which feature becomes strikingly evident at the lowest temperature employed. ``Arrhenius'' plots were made of the HCl–Ar, HCl–Xe, and the dimer data. The heats of formation were found to be 1.1, 1.6, and 2.14 kcal/mole, respectively, with a probable error of ±0.2 kcal/mole. The concentration of the dimer is estimated to be 1 part in 50 000 at 195°K at a gas density of 0.36 amagat.

A General Theory for Frequency Discriminators Containing Null Networks

The characteristics of the ring demodulator and of null networks have suggested a generalized approach to the design of discriminators containing null networks. In the past, discriminators using null networks have been designed about various types of demodulators in which a carrier signal is necessary, the design fundamental being that the phase difference between the signal and carrier voltages applied to the demodulator should change by 180 degrees at the null frequency and be a multiple of pi radians immediately above and below the null frequency. However, since the phase difference has not been an even number of pi radians as the frequency departs from the null region, the output of the discriminator becomes sensitive to the amplitudes of both the signal and carrier voltages. The generalized theory presented in this paper permits the design of discriminators containing null networks where, neglecting second-order effects, coupling capacitors, and the like, the phase difference is maintained a multiple of pi radians at all frequencies. The result is an inherently wide-band discriminator which can be constructed largely from unbalanced networks and which can be accurately calibrated. It is further possible to design discriminators of arbitrary sensitivities to the point where, neglecting noise, the discriminator behaves more as a frequency switch. The mechanization of the theory involves phase-equalizing networks in both the signal and carrier input systems to the demodulator. The general theory is concerned with admissible network functions consistent with the desire to maintain phase differences at a multiple of pi radians.