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NASA NTRS2008

Mitigating Photon Jitter in Optical PPM Communication

A theoretical analysis of photon-arrival jitter in an optical pulse-position-modulation (PPM) communication channel has been performed, and now constitutes the basis of a methodology for designing receivers to compensate so that errors attributable to photon-arrival jitter would be minimized or nearly minimized. Photon-arrival jitter is an uncertainty in the estimated time of arrival of a photon relative to the boundaries of a PPM time slot. Photon-arrival jitter is attributable to two main causes: (1) receiver synchronization error [error in the receiver operation of partitioning time into PPM slots] and (2) random delay between the time of arrival of a photon at a detector and the generation, by the detector circuitry, of a pulse in response to the photon. For channels with sufficiently long time slots, photon-arrival jitter is negligible. However, as durations of PPM time slots are reduced in efforts to increase throughputs of optical PPM communication channels, photon-arrival jitter becomes a significant source of error, leading to significant degradation of performance if not taken into account in design. For the purpose of the analysis, a receiver was assumed to operate in a photon- starved regime, in which photon counts follow a Poisson distribution. The analysis included derivation of exact equations for symbol likelihoods in the presence of photon-arrival jitter. These equations describe what is well known in the art as a matched filter for a channel containing Gaussian noise. These equations would yield an optimum receiver if they could be implemented in practice. Because the exact equations may be too complex to implement in practice, approximations that would yield suboptimal receivers were also derived.

Moision, Bruce↗
NASA NTRS2009

CCSDS Mission Operations Action Service Core Capabilities

This slide presentation reviews the operations concepts of the command (action) services. Since the consequences of sending the wrong command are unacceptable, the command system provides a collaborative and distributed work environment for flight controllers and operators. The system prescribes a review and approval process where each command is viewed by other individuals before being sent to the vehicle. The action service needs additional capabilities to support he operations concepts of manned space flight. These are : (1) Action Service methods (2) Action attributes (3) Action parameter/argument attributes (4 ) Support for dynamically maintained action data. (5) Publish subscri be capabilities.

Reynolds, Walter F.↗
NASA NTRS2009

Use of Acoustic Emission to Monitor Progressive Damage Accumulation in Kevlar (R) 49 Composites

Acoustic emission (AE) data acquired during intermittent load hold tensile testing of epoxy impregnated Kevlar(Registeres TradeMark) 49 (K/Ep) composite strands were analyzed to monitor progressive damage during the approach to tensile failure. Insight into the progressive damage of K/Ep strands was gained by monitoring AE event rate and energy. Source location based on energy attenuation and arrival time data was used to discern between significant AE attributable to microstructural damage and spurious AE attributable to noise. One of the significant findings was the observation of increasing violation of the Kaiser effect (Felicity ratio < 1.0) with damage accumulation. The efficacy of three different intermittent load hold stress schedules that allowed the Felicity ratio to be determined analytically is discussed.

Waller, Jess M.↗
NASA NTRS2009

Large Eddy Simulation of Transonic Flow Field in NASA Rotor 37

The current paper reports on numerical investigations on the flow characteristics in a transonic axial compressor, NASA Rotor 37. The flow field was used previously as a CFD blind test case conducted by American Society of Mechanical Engineers in 1994. Since the CFD blind-test exercise, many numerical studies on the flow field in the NASA Rotor 37 have been reported. Although steady improvements have been reported in both numerical procedure and turbulence closure, it is believed that all the important aspects of the flow field have not been fully explained with numerical studies based on the Reynolds Averaged Navier-Stokes (RANS) solution. Experimental data show large dip in total pressure distribution near the hub at downstream of the rotor at 100% rotor speed. Most original numerical solutions from the blind test exercise did not predict this total pressure deficit correctly. This total pressure deficit at the rotor exit was attributed to a hub corner flow separation by the author. Several subsequent numerical studies with different turbulence closure model also calculated this dip in total pressure rise. Also, several studies attributed this total pressure deficit to a small leakage flow coming from the hub in the test article. As the experimental study cannot be repeated, either explanation cannot be validated. The primary purpose of the current investigation is to investigate the transonic flow field with both RANS and a Large Eddy Simulation (LES). The RANS approach gives similar results presented at the original blind test exercise. Although the RANS calculates higher overall total pressure rise, the total pressure deficit near the hub is calculated correctly. The numerical solution shows that the total pressure deficit is due to a hub corner flow separation. The calculated pressure rise from the LES agrees better with the measured total pressure rise especially near the casing area where the passage shock interacts with the tip clearance vortex and flow becomes unsteady due to this interaction. The LES simulation also calculates the total pressure rise deficit near the hub and it agrees well with the measured data.

Hah, Chunill↗
NASA NTRS2009

In-Situ NDE Characterization of Kevlar and Carbon Composite Micromechanics for Improved COPV Health Monitoring

This project is a subtask of a multi-center project to advance the state-of-the-art by developing NDE techniques that are capable of evaluating stress rupture (SR) degradation in Kevlar/epoxy (K/Ep) composite overwrapped pressure vessels (COPVs), and damage progression in carbon/epoxy (C/Ep) COPVs. In this subtask, acoustic emission (AE) data acquired during intermittent load hold tensile testing of K/Ep and C/Ep composite tow materials-of-construction used in COPV fabrication were analyzed to monitor progressive damage during the approach to tensile failure. Insight into the progressive damage of composite tow was gained by monitoring AE event rate, energy, source location, and frequency. Source location based on arrival time data was used to discern between significant AE attributable to microstructural damage and spurious AE attributable to background and grip noise. One of the significant findings was the observation of increasing violation of the Kaiser effect (Felicity ratio < 1.0) with damage accumulation.

Waller, Jess M.↗
NASA NTRS2007

Advanced Reference Counting Pointers for Better Performance

A computer program implements reference counting pointers (RCPs) that are lock-free, thread-safe, async-safe, and operational on a multiprocessor computer. RCPs are powerful and convenient means of managing heap memory in C++ software. Most prior RCP programs use locks to ensure thread safety and manage concurrency. The present program was developed in a continuing effort to explore ways of using the C++ programming language to develop safety-critical and mission- critical software. This effort includes exploration of lock-free algorithms because they offer potential to avoid some costly and difficult verification problems. Unlike previously published RCP software, the present program does not use locks (meaning that no thread can block progress on another thread): Instead, this program implements algorithms that exploit capabilities of central-processing- unit hardware so as to avoid locks. Once locks are eliminated, it becomes possible to realize the other attributes mentioned in the first sentence. In addition to the abovementioned attributes, this program offers several advantages over other RCP programs that use locks: It is smaller (and, hence, is faster and uses less memory), it is immune to priority inversion, and there is no way for it to cause a C++ exception.

Reinholtz, William↗
NASA NTRS2007

Loss-of-Control-Inhibitor Systems for Aircraft

Systems to provide improved tactile feedback to aircraft pilots are being developed to help the pilots maintain harmony between their control actions and the positions of aircraft control surfaces, thereby helping to prevent loss of control. A system of this type, denoted a loss-of-control-inhibitor system (LOCIS) can be implemented as a relatively simple addition to almost any pre-existing flight-control system. The LOCIS concept offers at least a partial solution to the problem of (1) keeping a pilot aware of the state of the control system and the aircraft and (2) maintaining sufficient control under conditions that, as described below, have been known to lead to loss of control. Current commercial aircraft exhibit uneven responses of primary flight-control surfaces to aggressive pilot control commands, leading to deterioration of pilots ability to control their aircraft. In severe cases, this phenomenon can result in loss of control and consequent loss of aircraft. For an older aircraft equipped with a purely mechanical control system, the loss of harmony between a pilot s command action and the control- surface response can be attributed to compliance in the control system (caused, for example, by stretching of control cables, flexing of push rods, or servo-valve distortion). In a newer aircraft equipped with a fly-by-wire control system, the major contributions to loss of harmony between the pilot and the control surfaces are delays attributable to computer cycle time, control shaping, filtering, aliasing, servo-valve distortion, and actuator rate limiting. In addition, a fly-by-wire control system provides no tactile feedback that would enable the pilot to sense such features of the control state as surface flutter, surface jam, position limiting, actuator rate limiting, and control limiting imposed by the aircraft operational envelope. Hence, for example, when a pilot is involved in aggressive closed-loop maneuvering, as when encountering a wake-vortex upset on final landing approach, the control-surface delay can lead to loss of control. Aggressive piloting can be triggered and exacerbated by control-system anomalies, which the pilot cannot diagnose because of the lack of symptoms caused by the absence of feedback through the controls. The purpose served by a LOCIS is to counteract these adverse effects by providing real-time feedback that notifies the pilot that the aircraft is tending to lag the pilot s commands. A LOCIS (see figure) includes cockpit control input-position sensors, control-surface output-position sensors, variable dampers (for example, shock absorbers containing magneto-rheological fluids such that the damping forces can be varied within times of the order of milliseconds by varying applied magnetic fields) attached to the cockpit control levers, electromagnet coils to apply the magnetic fields, and feedback control circuits to drive the electromagnet coils. The feedback control gains are chosen so that the current applied to each electromagnet coil results in a damping force that increases in a suitable nonlinear manner (e.g., exponentially) with the difference between the actual and commanded positions of the affected control surface. The increasing damping force both alerts the pilot to the onset of a potentially dangerous situation and resists the pilot s effort to command a control surface to change position at an excessive rate

AHarrah, Ralph C.↗
NASA NTRS2010

Observing Supernova 1987A with the Refurbished Hubble Space Telescope

The young remnant of supernova 1987A (SN 1987A) offers an unprecedented glimpse into the hydrodynamics and kinetics of fast astrophysical shocks. We have been monitoring SN 1987A with the Hubble Space Telescope (HST) since it was launched. The recent repair of the Space Telescope Imaging Spectrograph (STIS) allows us to compare observations in 2004, just before its demise, with those in 2010, shortly after its resuscitation by NASA astronauts. We find that the Ly-alpha and H-alpha lines from shock emission continue to brighten, while their maximum velocities continue to decrease. We report evidence for nearly coherent, resonant scattering of Lya photons (to blueshifts approximately -12,000 km /s) from hotspots on the equatorial ring. We also report emission to the red of Ly-alpha that we attribute to N v lambda lambda 1239,1243 Angstrom line emission. These lines are detectable because, unlike hydrogen atoms, N4+ ions emit hundreds of photons before they are ionized. The profiles of the N v lines differ markedly from that of H-alpha. We attribute this to scattering of N4+ ions by magnetic fields in the ionized plasma. Thus, N v emission provides a unique probe of the isotropization zone of the collisionless shock. Observations with the recently installed Cosmic Origins Spectrograph (COS) will enable us to observe the N v lambda lambda 1239,1243 Angstrom line profiles with much higher signal-to-noise ratios than possible with STIS and may reveal lines of other highly ionized species (such as C IVlambda lambda 1548,1551 Angstrom) that will test our explanation for the N v emission

France, Kevin↗
NASA NTRS2010

Optimizing Medical Kits for Space Flight

The Integrated Medical Model (IMM) uses Monte Carlo methodologies to predict the occurrence of medical events, their mitigation, and the resources required during space flight. The model includes two modules that utilize output from a single model simulation to identify an optimized medical kit for a specified mission scenario. This poster describes two flexible optimization routines built into SAS 9.1. The first routine utilizes a systematic process of elimination to maximize (or minimize) outcomes subject to attribute constraints. The second routine uses a search and mutate approach to minimize medical kit attributes given a set of outcome constraints. There are currently 273 unique resources identified that are used to treat at least one of 83 medical conditions currently in the model.

Minard, Charles G.↗
NASA NTRS2010

Implication of the Observable Spectral Cutoff Energy Evolution in XTE J1550-564

The physical mechanisms responsible for production of the non-thermal emission in accreting black holes should be imprinted in the observational appearances of the power law tails in the X-ray spectra from these objects. Variety of spectral states observed from galactic black hole binaries by it Rossi X-ray Timing Explorer (RXTE) allow examination of the photon upscattering under different accretion regimes. We revisit of RXTE data collected from the black hole X-ray binary XTE J1550-564 during two periods of X-ray activity in 1998 and 2000 focusing on the behavior of the high energy cutoff of the power law part of the spectrum. For the 1998 outburst the Iran- sition from the low-hard state to the intermediate state was accompanied by a gradual decrease in the cutoff energy which then showed a sharp reversal to a clear increasing trend during the further evolution towards the very high and high-soft states. However, the 2000 outburst showed only the decreasing part of this pattern. Notably, the photon indexes corresponding to the cutoff increase for the 1998 event are much higher than the index values reached during the 2000 rise transition. We attribute this difference in the cutoff' energy behav- for to the different partial contributions of the thermal and non-thermal (bulk motion) Comptonization in photon upscattering. Namely, during the 1998 event the higher accretion rate presumably provided more cooling to the Comptonizing media and thus reducing the effectiveness of the thermal upscattering process. Under these conditions the bulk motion takes a leading role in boosting the input soft photons. Monte Carlo simulations of the The physical mechanisms responsible for production of the non-thermal emission in accreting black holes should be imprinted in the observational apperances of the power law tails in the X-ray spectra from these objects. Variety of spectral states observed from galactic black hole binaries by it Rossi X-ray Timing Explorer (RXTE) allow examination of the photon upscattering under different accretion regimes. We revisit of RXTE data collected from the black hole X-ray binary XTE J1550-564 during two periods of X-ray activity in 1998 and 2000 focusing on the behavior of the high energy cutoff of the power law part of the spectrum. For the 1998 outburst the Iran- sition from the low-hard state to the intermediate state was accompanied by a gradual decrease in the cutoff energy which then showed a sharp reversal to a clear increasing trend during the further evolution towards the very high and high-soft states. However, the 2000 outburst showed only the decreasing part of this pattern. Notably, the photon indexes corresponding to the cutoff increase for the 1998 event are much higher than the index values reached during the 2000 rise transition. We attribute this difference in the cutoff' energy behav- for to the different partial contributions of the thermal and non-thermal (bulk motion) Comptonization in photon upscattering. Namely, during the 1998 event the higher accretion rate presumably provided more cooling to the Comptonizing media and thus reducing the effectiveness of the thermal upscattering process. Under these conditions the bulk motion takes a leading role in boosting the input soft photons. Monte Carlo simulations of the Comptonization in a bulk motion region near an accreting black hole by Laurent & Titarchuk (2010) strongly support this scenario. strongly support this scenario

Titarchuk, Lev↗
NASA NTRS2000

Factors Contributing to Pilot Valve Fuel Seal Extrusion in Orbiter PRCS Thrusters

Extrusion of the polytetrafluoroethylene (PTFE) pilot seal used in the monomethylhydrazine (fuel) valve of the Orbiter Primary Reaction Control System (PRCS) thrusters has been implicated in numerous on-orbit thruster failures and on-ground valve failures. Two extrusion mechanisms have been proposed, one or both may be occurring. The first mechanism is attributed to thermal expansion mismatch between adjacent PTFE and metal parts used in the fuel valve, and is referred to as thermal extrusion. The second mechanism is attributed to nitrogen tetroxide (oxidizer) leakage from the adjacent oxidizer valve on the same thruster during ground turnaround, and is referred to as oxidizer-induced extrusion. Model calculations of PTFE pilot seal in an exact pilot valve configuration show that extrusion can be caused by differential thermal expansion, without the intervening influence of oxidizer. Experimental data on semitrapped PTFE and TFM (modified PTFE) specimens simulating a fuel pilot valve configuration show that thermal extrusion 1) is incremental and irreversible, 2) increases with the size of the thermal excursion, 3) decreases with successive thermal cycling, and 4) is accompanied by gap formation. Both PTFE and TFM exhibit a higher affinity for oxidizer than fuel. The property changes associated with oxidizer uptake may explain why oxidizer seals do not exhibit extrusion. Impression replicas of fuel pilot seals removed from the Orbiter fleet show two types of extrusion: extrusion of the entire seal (loaded extrusion), or extrusion of non-sealing surface (unloaded extrusion). Both extrusion types may arise from differences in service history, rather than in failure mechanism. The plausibility oxidizer-induced extrusion was evaluated. Preliminary calculations suggest that enough energy, heat, or gas may be liberated under certain operational scenarios to cause catastrophic extrusion. However, given the lack of supporting data, conclusions implicating oxidizer leakage as a factor in extrusion must be made with caution.

Waller, J.M.↗
NASA NTRS2010

Summary of the Large Civil Tiltrotor (LCTR2) Engine Gearbox Study

In support of the Fundamental Aeronautics Program, Subsonic Rotary Wing Project, NASA is continuing to study the Large Civil Tiltrotor (LCTR) concept to help define/refine vehicle, system and subsystem attributes. These attributes can then be used to define performance requirements and identify new or advanced technologies to achieve an operational vehicle class. As part of this goal, NASA contracted with The Boeing Company and its subcontractor Rolls-Royce to perform an investigation of different combinations of engine and gearbox variability to achieve a maximum of 50 percent rotor tip speed reduction from hover to cruise conditions. Previous NASA studies identified the 50 percent rotor speed reduction minimized vehicle gross weight and fuel burn. The LCTR2 (LCTR-iteration 2) was the contracted study baseline for initial sizing. Rotor tip speed ratios (cruise to hover) of 100, 77, and 54 percent were analyzed for each combination of engine and gearbox speed reduction to achieve the chosen rotor tip speed ratio. Three different engine and gearbox technology levels were assumed; commercial off-the-shelf (COTS), entry-in-service (EIS) in 2025 and EIS in 2035. These technology levels were applied to determine each particular effect on vehicle gross weight and fuel burn, while other vehicle technologies were assumed constant. This report summarizes the work performed that is being put together into a comprehensive NASA contractor report. Some background on the LCTR concept and baseline vehicle will be given and then a discussion concerning the technical approach utilized. Major study assumptions and results will be presented and discussed. Finally conclusions will be drawn as well as suggestions provided for future efforts.

Snyder, Christopher A.↗
NASA NTRS2010

Employing Geodatabases for Planetary Mapping Conduct - Requirements, Concepts and Solutions

Planetary geologic mapping has become complex in terms of merging and co-registering a variety of different datasets for analysis and mapping. But it has also become more convenient when it comes to conducting actual (geoscientific) mapping with the help of desktop Geographic Information Systems (GIS). The complexity and variety of data, however, are major issues that need to be taken care of in order to provide mappers with a consistent and easy-to-use mapping basis. Furthermore, a high degree of functionality and interoperability of various commercial and open-source GIS and remote sensing applications allow mappers to organize map data, map components and attribute data in a more sophisticated and intuitional way when compared to workflows 15 years ago. Integration of mapping results of different groups becomes an awkward task as each mapper follows his/her own style, especially if mapping conduct is not coordinated and organized programmatically. Problems of data homogenization start with various interpretations and implementations of planetary map projections and reference systems which form the core component of any mapping and analysis work. If the data basis is inconsistent, mapping results in terms of objects georeference become hard to integrate. Apart from data organization and referencing issues, which are important on the mapping as well as the data-processing side of every project, the organization of planetary geologic map units and attributes, as well as their representation within a common GIS environment, are key components that need to be taken care of in a consistent and persistent way.

vanGasselt, Stephan↗
NASA NTRS2011

Using High-Resolution Forward Model Simulations of Ideal Atmospheric Tracers to Assess the Spatial Information Content of Inverse CO2 Flux Estimates

Attribution of observed atmospheric carbon concentrations to emissions on the country, state or city level is often inferred using "inversion" techniques. Such computations are often performed using advanced mathematical techniques, such as synthesis inversion or four-dimensional variational analysis, that invoke tracing observed atmospheric concentrations backwards through a transport model to a source region. It is, to date, not well understood how well such techniques can represent fine spatial (and temporal) structure in the inverted flux fields. This question is addressed using forward-model computations with idealized tracers emitted at the surface in a large number of grid boxes over selected regions and examining how distinctly these emitted tracers can be detected downstream. Initial results show that tracers emitted in half-degree grid boxes over a large region of the Eastern USA cannot be distinguished from each other, even at short distances over the Atlantic Ocean, when they are emitted in grid boxes separated by less than five degrees of latitude - especially when only total-column observations are available. A large number of forward model simulations, with varying meteorological conditions, are used to assess how distinctly three types observations (total column, upper tropospheric column, and surface mixing ratio) can separate emissions from different sources. Inferences inverse modeling and source attribution will be drawn.

Pawson, Steven↗
NASA NTRS2011

Feature Acquisition with Imbalanced Training Data

This work considers cost-sensitive feature acquisition that attempts to classify a candidate datapoint from incomplete information. In this task, an agent acquires features of the datapoint using one or more costly diagnostic tests, and eventually ascribes a classification label. A cost function describes both the penalties for feature acquisition, as well as misclassification errors. A common solution is a Cost Sensitive Decision Tree (CSDT), a branching sequence of tests with features acquired at interior decision points and class assignment at the leaves. CSDT's can incorporate a wide range of diagnostic tests and can reflect arbitrary cost structures. They are particularly useful for online applications due to their low computational overhead. In this innovation, CSDT's are applied to cost-sensitive feature acquisition where the goal is to recognize very rare or unique phenomena in real time. Example applications from this domain include four areas. In stream processing, one seeks unique events in a real time data stream that is too large to store. In fault protection, a system must adapt quickly to react to anticipated errors by triggering repair activities or follow- up diagnostics. With real-time sensor networks, one seeks to classify unique, new events as they occur. With observational sciences, a new generation of instrumentation seeks unique events through online analysis of large observational datasets. This work presents a solution based on transfer learning principles that permits principled CSDT learning while exploiting any prior knowledge of the designer to correct both between-class and withinclass imbalance. Training examples are adaptively reweighted based on a decomposition of the data attributes. The result is a new, nonparametric representation that matches the anticipated attribute distribution for the target events.

Thompson, David R.↗
NASA NTRS2006

Using Artificial Intelligence to Inform Pilots of Weather

An automated system to assist a General Aviation (GA) pilot in improving situational awareness of weather in flight is now undergoing development. This development is prompted by the observation that most fatal GA accidents are attributable to loss of weather awareness. Loss of weather awareness, in turn, has been attributed to the difficulty of interpreting traditional preflight weather briefings and the difficulty of both obtaining and interpreting traditional in-flight weather briefings. The developmental automated system not only improves weather awareness but also substantially reduces the time a pilot must spend in acquiring and maintaining weather awareness.

Spirkovska, Lilly↗
NASA NTRS2011

United Space Alliance, LLC Windchill As-Built Highlights

Work Order execution data from Solumina As Worked BOM (As-Built) in Solumina (Slide 2) sent to Windchill Windchill receives As Worked BOM data and 'marries' the Solumina execution data to the Part Instance/Product Structure/As-Design (Slide 3 As-Design and Slide 4 &5 As-Built) Manage the As-Built to As-Design delta's via the interface and Part Instance Attributes (Slide 6) including Work Order data and any CMcomments Produce an As-Built to As-Design report that also includes all Part Instance Attribute data (no screenshot as this is still in development) Utilize Windchill and Solumina 'Out of the Box' functionality

Richmond, Dena M.↗
NASA NTRS2011

Increased Intracranial Pressure and Visual Impairment Associated with Long-Duration Spaceflight

Although humans have been flying in space since the 1960s, more recent missions have revealed a new suite of physiological adaptations and consequences of space flight. Notably, 60% of long-duration crewmembers (ISS/MIR) and >25% of short-duration (Shuttle) crewmembers have reported subjective degradation in vision (based on debrief comments) (Gibson 2011). Decreased near-visual acuity was demonstrated in 46% of ISS/Mir and 21% of Shuttle crewmembers, resulting in a shift of up to 1-2 diopters in their refractive correction. It is likely that the recently revealed ophthalmic changes have been present since the first days of human space flight, but have been overlooked or attributed to other causations. The reported changes in vision have occurred at various time points throughout missions, with ranging degrees of visual degradation. Although some cases resolved upon return to Earth, several astronauts have not regained preflight visual acuity, indicating that the damage may be permanent. While observing these changes over the years, without other overt symptomology and with the given age range of the flying population, this has largely been attributed to an expected hyperopic shift due to aging. However, the availability of onboard analysis techniques, including visual acuity assessments, retinal imagery, and ultrasounds of the eye and optic nerve tracts, along with more detailed post-flight techniques, has led to the recent recognition of a wider syndrome. Along with vision changes, findings include flattening of the globe, swelling of the optic disc (papilledema), choroidal folds in the retina, swelling of the optic nerve sheath, and visual field defects. It is widely hypothesized that this constellation of findings may be explained by an elevation of intracranial pressure (ICP). Out of the 60% of long-duration astronauts that have reported a subjective degradation in vision, a subset (currently 10 astronauts) have developed this syndrome. The National Aeronautics and Space Administration (NASA) has made it a high priority to understand this syndrome and provide mitigation techniques to protect crewmembers from visual impairment. While there are many possible factors that could contribute to intracranial hypertension associated with spaceflight, the relative contribution of these, as well as the processes by which eye damage occurs as a result of intracranial hypertension, are not fully understood. The observed pathophysiological phenomena are extremely complex and it is likely that multiple factors contribute to their incidence, rather than one simple mechanism. This paper will define and examine the findings in detail, and expound upon the potential contributing factors and their relative contribution to this syndrome.

Marshall-Bowman, Karina↗