PURPOSE:To evaluate the duty cycle of different vitrectomy cutters and classify their blade movement.METHODS:A precise weighing (0.01 g) high speed (2 samples/s) balance was used to study the 20-gauge and 25-gauge Bausch & Lomb Lightning-Millenium (St. Louis, MO), the 20-gauge (1500 cpm) and the 25-gauge Alcon Accurus (Fort Worth, TX), the 20-gauge Alcon Innovit, and the 23-gauge DORC (Netherlands) cutters. The weight of balanced saline solution (BSS) was recorded in real time using LabView software and then translated into a graph of volume removed versus time. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. A high-speed (400 frames/s) camera was used to record cutting for each condition.RESULTS:Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic). The parabolic incomplete and trapezoid had a decreased duty cycle at 1500 cuts per minute when it was compared to 600 cuts per minute. The sinusoid had no statistical difference between cut rates.CONCLUSIONS:Systems showed different performances of duty cycle. This new classification will be useful for improved understanding of vitrectomy in these different systems.

Purpose: To evaluate porcine vitreous flow and balanced saline solution (BSS) flow rates in different vitrectomy systems. Methods: Porcine vitreous was obtained within 24 hours of slaughter. A high-speed (2 samples/s) balance, precise to 0.01 g, was used. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. The vitreous was labeled with glass microspheres and triamcinolone acetonide. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: For all cutters, there was no vitreous flow at zero cut rates (off). In 25-gauge cutters, at 500 mmHg of vacuum, the electric cutter produced higher average flow rates at high cut rates (600 cpm, 0.004 mL/s, and 1500 cpm, 0.013 mL/s) than pneumatic, which demonstrated a decreased flow at speeds higher than 1000 cpm (1000 cpm, 0.015 mL/s, and 1500 cpm, 0.006 mL/s). The percentage of vitreous flow rate/BSS flow rate in different aspiration and cut rates showed an ascending curve. This demonstrates evidence of flow obstruction in 25- (all cut rates), 23- (all cut rates), and 20-gauge (all cut rates). Flow obstruction and surge movements were seen in the high-speed videos. Conclusions: The vitrectomy systems each illustrate different performances of vitreous removal. The physical characteristics of vitreous resulted in nonuniform flow in all vitreous cutters.

PURPOSE: To design an improved self,stabilizing lens ring for 25-gauge vitrectomy.DESIGN: Device report.METHODS: A lens ring was designed to be fixated to the globe using 25-gauge transconjunctival cannulas.RESULTS: This ring consists of a single plastic component with multiple concavities at the ring margin to fit 25-gauge cannulas. The ring can accommodate conventional standard and panoramic vitrectomy lenses.CONCLUSIONS: A lens ring has been designed for 25-gauge vitrectomy and to hold conventional contact lenses. Stability of the lens ring is achieved without the need for sutures and instead is achieved by the three point fixation provided by the existing 25-gauge cannula system.

This paper is a brief survey of theoretical expectations for the geometry of the heliospheric termination shock.

In this paper we use the best currently available estimates for interstellar parameters to calculate several models of the interaction between the solar wind and the magnetized interstellar plasma in the presence of LISM neutral hydrogen. We show how the heliosphere may be modified by both the galactic magnetic field and neutral particles.

This paper reviews the role that the exterior magnetic field (of interstellar origin) and the interior magnetic field (of solar origin) may play in the heliosphere-LISM interaction.

We use the best currently available estimates for interstellar parameters to update and expand the earlier study of Ratkiewicz et al. [1998]. We report (1) a more complete survey of the morphology of the heliosphere and the ways it may be modified by variation of external interstellar parameters, (2) a detailed classification of the several asymmetries and distortions associated with exterior field‐flow obliquity, including cross sections of the three‐dimensional structure in all three principal planes, (3) an analysis of the transition from supermagnetosonic to nearly transmagnetosonic flow, and (4) specific results for the heliosphere for the best current understanding of conditions in the local interstellar medium.

The heliospheric termination shock must exhibit asymmetry in its shape, due in part to internal latitude variations in the solar wind, and in part to the special directions defined by the external interstellar flow and/or the galactic magnetic field. This asymmetry shows up naturally in numerical simulations of the interaction between the heliosphere and local interstellar medium. However, to date only one analytical treatment of the theory has appeared (Barnes, 1998), which discussed the modification of the shock shape due to solar wind latitude variations in the presence of spherically symmetric outer boundary conditions. In the present report, we discuss an extension and generalization of this theory to an axially symmetric gasdynamic system, in which departure from spherical symmetry may be due either to internal solar wind variations or to the directional properties of the external interstellar medium. It is shown that for steady flow the post-shock region is characterized by an infinite set of quantities that are conserved along streamlines; among these invariants are the stagnation pressure and a quantity closely related to vorticity. Moreover, for a given latitude profile of the (supersonic) solar wind, the geometry of the termination shock uniquely determines the value of these invariants at the points where the streamlines emerge from the shock. In the case of flow into a static interstellar medium for which the appropriate boundary condition is that the stagnation pressure is the same for all streamlines, it can be shown that the location and shape of the termination shock, together with the entire heliosheath now, are completely determined by the external pressure plus the internal solar wind parameters. However, for even a slightly nonstatic interstellar flow, or for anisotropy in exterior conditions from any other cause, such as the galactic magnetic field, exterior interstellar plus interior solar-wind conditions do not uniquely determine the heliosheath flow field or the shape of the termination shock. A complete solution requires specification of additional conditions, such as the run of dynamic pressure across the distant wake, or the requirement that the heliosheath flow be vorticity-free.

The aim of this paper is to present the effects of varying magnitude and orientation of the local interstellar mag- netic field on the heliospheric boundary region (the region be- tween the termination shock and the bow shock containing the heliopause). Other effects such as interstellar neutrals, cosmic rays and the asymmetry of the solar wind caused by its heli- olatitude dependence are disregarded. We calculate the shape and structure of the heliospheric boundary region for different interstellar Alfv ´ enic Mach numbers and various inclination an- gles between Very Local InterStellar Medium (VLISM) velocity and magnetic field vectors using a fully three-dimensional MHD computational analysis. The new results show the asymmetry of this region for inclination angles 0 << 90 and are in agreement with the Newtonian approximation theory (Fahr et al. 1986, 1988) concerning trends in the heliopause orientation and location. Unlike the NA model which only qualitatively indicates the effects of the VLISM magnetic field on the he- liospheric boundary region the present 3D MHD calculations reveal fully the nature of these effects by capturing all discon- tinuities including the termination shock, heliopause and bow shock. The numerical scheme employed in this study is fully im- plicit and conservative, using a Roe-type Riemann solver in a generalized coordinate system.

We investigate the consequences of internal solar wind latitude variations on the heliospheric termination shock and the flow of the gas beyond the shock. We have developed a simple gasdynamic model, assuming the solar wind to be a steady, axially symmetric radial outflow of gas that passes through a termination shock and flows incompressibly beyond the shock. We ignore any latitude variations external to the heliosphere (i.e., due to the local interstellar medium) by requiring that the stagnation pressure infinitely far away must be spherically symmetric. Analysis of the model leads to three broad conclusions: (1) The shape of the heliospheric shock is qualitatively similar to what one would predict using the “naive” assumption that the heliocentric distance of the shock is proportional to the square root of the scaled solar wind dynamic pressure ρvr2. (2) However, the existence of an internal latitude dependence of the scaled dynamic pressure requires that the shock must be oblique at some latitudes, and this obliquity produces an outward “bulge” in the shape of the termination shock; this conclusion is completely general, and in particular is true for the case of an oblate shock. (3) For a prolate termination shock the far‐down‐stream flow is deflected toward the equator, and solar wind originating in the poleward half of (say) the northern hemisphere would fill more than half of the volume of the same hemisphere beyond the termination shock; the deflection would be in the opposite sense (poleward) for an oblate termination shock.

The unsteady spherically symmetric one-dimensional gasdynamic model appears to be a powerful tool in the investigation of the termination shock motion. Such a model has previously been used to examine the response of the heliospheric termination shock to variations in upstream solar wind conditions [Ratkiewicz et al., 1996]. In the current paper we apply the same model to study response of the shock to variations in the interstellar medium. The initial-boundary conditions for the unsteady calculations are given by the pressure as a function Of time on an outer boundary either alone or with the density as a function of time on an inner boundary. The motion of the termination shock is caused by fluctuations in both solar wind and interstellar plasma parameters and has a rather complicated behavior, characterized by a sequence of perturbations that hit the termination shock and are reflected from the outer boundary.

Observations of solar Lyman alpha have been interpreted as indicating that the solar wind mass flux density is lower at polar latitudes than at equatorial latitudes. This led Lallement et al [1986] to make a parametric study of solar wind acceleration, along the fines of the earlier Munro-Jackson study [1977], in which they concluded that uncertainties in the polar mass flux were large enough to be consistent with two extreme opposites: (1) a substantial energy supply beyond classical thermal conduction is required, or (2) classical thermal conduction is adequate to drive the flow. This ambiguity has been clarified by Ulysses observations of the polar outflow [Phillips et al, 1995]. The polar mass flux density Lies near or somewhat above the middle of the range studies by Lallement et al [1986], which indicates that extended heating is likely to be going on out to at least similar to 5 solar radii. Independent, purely energetic arguments can be made to estimate the required coronal source (electron) temperature that would be required to account for the observed energy flux density. An electron temperature of well above 2x10(6) K would be required for the classical conduction flux density to be comparable to the total energy flux density; such a high temperature is unlikely in a coronal hole. These arguments strongly suggest that some extended heating or momentum transfer mechanism is required to drive the solar wind from the polar coronal hole.

The heliospheric termination shock is expected to move in response to variation in upstream solar wind conditions. Using numerical techniques, we extend rm earlier strictly one-dimensional (planar) analytic gasdynamic model of shock motion [Barnes, 1993] to spherically symmetric [Ratkiewicz et al., 1995], to investigate the qualitative features of global behavior of shock motion. The boundary conditions of the calculation are given by the solar wind parameters as a function of time on an inner spherical boundary, and a constant pressure (roughly simulating the effect of the local interstellar medium) on an outer boundary.

Large-scale fluctuations in the solar wind plasma upstream of the heliospheric termination shock (TS) will cause inward and outward motions of the shock. Using numerical techniques, we extend an earlier strictly one-dimensional (planar) analytic gasdynamic model [Barnes, 1993] to spherical symmetry to investigate the features of global behavior of shock motion. Our starting point is to establish a steady numerical solution of the gasdynamic equations describing the interaction between the solar wind and the interstellar medium. We then introduce disturbances of the solar wind dynamic pressure at an inner boundary and follow the subsequent evolution of the system, especially the motion of the termination shock. Our model solves spherically symmetric gasdynamic equations as an initial-boundary value problem. The equations in conservative form are solved using a fully implicit total variation diminishing (TVD) upwind scheme with Roe-type Riemann solver. Boundary conditions are given by the solar wind parameters on an inner spherical boundary, where they are allowed to vary with time for unsteady calculations and by a constant pressure (roughly simulating the effect of the local interstellar medium) on an outer boundary. We find that immediately after the interaction, the shock moves with speeds given by the earlier analogous analytic models. However, as the termination shock propagates, it begins to slow down, seeking a new equilibrium position. In addition, the disturbance transmitted through the TS, either a shock or rarefaction wave, will encounter the outer boundary and be reflected back. The reflected signal will encounter the TS, causing it to oscillate. The phenomenon may be repeated for a number of reflections, resulting in a "ringing" of the outer heliosphere.

We review the observed properties of the solar wind in the outer heliosphere, including observations from Voyager and the Pioneers and also from inner heliospheric probes as appropriate. These observations are crucial to modeling of the heliosphere and its interactions with the interstellar medium, since the solar wind mm pressure and its temporal variations are important in understanding the distance to the termination shock and heliopause and how those boundaries might vary in time. We focus on results since Solar Wind 7. Among the issues we discuss are: (1) the time scales for and statistical properties of variations in the ram pressure in the outer heliosphere, and how those variations might affect the morphology of the heliospheric/interstellar medium interface; (2) the question of possible solar wind slowing in the outer heliosphere due to the pick-up of interstellar ions; (3) the issue of whether there is bulk heating of the solar wind associated either with interstellar ion pick-up or with continuing heating due to stream-stream interactions; (4) evidence for latitudinal variations in solar wind properties; and (5) the 1.3 year periodicities apparent in the outer heliosphere and the dose correspondence of these periodicities with similar variations observed in the inner heliosphere.

We present Ulysses solar wind plasma data from the peak southerly latitude of −80.2° on 12 September 1994 through the corresponding northerly latitude on 31 July 1995. Ulysses encountered fast wind throughout this time except for a 43° band centered on the solar equator. Median mass flux was nearly constant with latitude, while speed and density had positive and negative poleward gradients, respectively. Solar wind momentum flux was highest at high latitudes, suggesting a latitudinal asymmetry in the heliopause cross section. Solar wind energy flux density was also highest at high latitudes.

We expect the mean distance of the heliospheric termination shock to be greater (smaller) at polar latitudes than at equatorial latitudes, depending on whether the mean dynamic pressure of the solar wind is greater or smaller at high latitudes. The heliospheric termination shock is expected to move in response to variation in upstream solar wind conditions, so that at any particular instant the termination shock will resemble a distorted asymmetric balloon with some parts moving inward and others moving outward. If the shock is a gasdynamic or magnetohydrodynamic shock the results of the analysis depend only very weakly on the nature of the upstream disturbance; typical speeds of the disturbed shock are ∼100 to 200 km/s. In the absence of a significant latitude gradient of the typical magnitude of solar wind disturbances typical motions of the disturbed shock at polar latitudes would be about twice as fast, due to the higher speed of the high-latitude wind. If the dynamics of the termination shock are dominated by acceleration of the aromalous component of the cosmic rays, the motion of the shock in response to a given disturbance is substantially slower than in the gasdynamic case. Conceivably, particle acceleration might be a less important effect at higher latitudes, and we envision the possibility of a termination shock that is dominated by particle acceleration at lower latitudes and is an MHD shock at high latitudes. In this event high latitude solar wind disturbances would produce substantially larger inward and outward motions of the shock in the polar regions.

Magnetic holes, localized depressions in the interplanetary magnetic field, have been identified in Ulysses data over a range of several AU and as far as 23 degrees south in latitude by Winterhalter et al., who concluded that these structures are most likely the remnants of structures caused by occasional mirror-mode instability in the solar wind. However, these authors, like a number of previous investigators, used the mirror stability criterion derived from the kinetic theory under very special assumptions. On the other hand, theoretical investigations using the fully self-consistent kinetic theory (Vlasov-Maxwell equations) have shown that the mirror stability criterion is more complicated when electrons and ions have different anisotropies, as is normally the case in the solar wind. Winterhalter et al used an instability criterion of the form R is greater than 1, where R is a function of the thermal anisotropy; the correct criterion (for bi-Maxwellian distributions) is R R is greater than 1 - x(exp 2), where x is a real quantity that depends on both the proton anisotropy and electron anisotropy. So nonzero x would modify the Winterhalter et al results in the direction of reinforcing their conclusions. We have revisited the instability criterion in its most general form, allowing for (a) non-Maxwellian velocity distributions, (b) multiple ion species, and (c) interparticle streaming. These results should give sound theoretical grounding for future observational studies related to the mirror instability, by Ulysses and other spacecraft.