3,816 research outputs found
Three dimensional tracking with misalignment between display and control axes
Human operators confronted with misaligned display and control frames of reference performed three dimensional, pursuit tracking in virtual environment and virtual space simulations. Analysis of the components of the tracking errors in the perspective displays presenting virtual space showed that components of the error due to visual motor misalignment may be linearly separated from those associated with the mismatch between display and control coordinate systems. Tracking performance improved with several hours practice despite previous reports that such improvement did not take place
A mathematical model for the sequestering of chemical contaminants by magnetic particles
A mathematical model is developed and implemented to characterize the pickup of various liquid chemical contaminants by
polyethylene-coated magnetic particles. The model and its associated experimental and analytical protocols were applied to a wide range
of liquid chemicals in order to gain insights into the physical basis for the pickup phenomenon. The characteristics of the pickup isotherms
range between āidealā and ānonidealā behaviors that are reflected in the mathematical model by a single parameter, ļæ½0, where ļæ½0=1
corresponds to ideal behavior and ļæ½0ļæ½1 corresponds to a departure from idealized behavior that is directly quantified by the magnitude
of ļæ½0. The parameter ļæ½0 is also related to the efficiency of pickup, and since most isotherms observed in the study deviate from ideality,
the high efficiency of pickup observed in these systems has been attributed in part to this deviation. The proposed model and its associated
experimental and analytical protocols demonstrate great potential for the systematic evaluation of the uptake of chemical contaminants
using magnetic particle technology
The Three-Dimensional Circumstellar Environment of SN 1987A
We present the detailed construction and analysis of the most complete map to
date of the circumstellar environment around SN 1987A, using ground and
space-based imaging from the past 16 years. PSF-matched difference-imaging
analyses of data from 1988 through 1997 reveal material between 1 and 28 ly
from the SN. Careful analyses allows the reconstruction of the probable
circumstellar environment, revealing a richly-structured bipolar nebula. An
outer, double-lobed ``Peanut,'' which is believed to be the contact
discontinuity between red supergiant and main sequence winds, is a prolate
shell extending 28 ly along the poles and 11 ly near the equator. Napoleon's
Hat, previously believed to be an independent structure, is the waist of this
Peanut, which is pinched to a radius of 6 ly. Interior to this is a cylindrical
hourglass, 1 ly in radius and 4 ly long, which connects to the Peanut by a
thick equatorial disk. The nebulae are inclined 41\degr south and 8\degr east
of the line of sight, slightly elliptical in cross section, and marginally
offset west of the SN. From the hourglass to the large, bipolar lobes, echo
fluxes suggest that the gas density drops from 1--3 cm^{-3} to >0.03 cm^{-3},
while the maximum dust-grain size increases from ~0.2 micron to 2 micron, and
the Si:C dust ratio decreases. The nebulae have a total mass of ~1.7 Msun. The
geometry of the three rings is studied, suggesting the northern and southern
rings are located 1.3 and 1.0 ly from the SN, while the equatorial ring is
elliptical (b/a < 0.98), and spatially offset in the same direction as the
hourglass.Comment: Accepted for publication in the ApJ Supplements. 38 pages in
apjemulate format, with 52 figure
The Effect of Use and Access on Citations
It has been shown (S. Lawrence, 2001, Nature, 411, 521) that journal articles
which have been posted without charge on the internet are more heavily cited
than those which have not been. Using data from the NASA Astrophysics Data
System (ads.harvard.edu) and from the ArXiv e-print archive at Cornell
University (arXiv.org) we examine the causes of this effect.Comment: Accepted for publication in Information Processing & Management,
special issue on scientometric
Olfactory groove meningioma: Discussion of clinical presentation and surgical outcomes following excision via the subcranial approach
Objectives/Hypothesis: To describe surgical outcomes and radiographic features of olfactory groove meningiomas treated by excision through the subcranial approach. Special emphasis is placed on paranasal sinus and orbit involvement. Study Design: Retrospective review of a series of patients. Methods: Nineteen patients underwent excision of olfactory groove meningioma (OGM) via the transglabellar/subcranial approach between December 1995 and November 2009. Nine patients had previously undergone prior resection at outside institutions, and four had prior radiotherapy in addition to a prior excision. Transglabellar/subcranial surgical approach to the anterior skull base was performed. Results: Tumor histology included three World Health Organization (WHO) grade III lesions, one WHO grade II lesion, and 15 WHO grade I lesions. Fourteen patients had evidence of extension into the paranasal sinuses, with the ethmoid sinus being most commonly involved. KaplanāMeier estimates of mean overall and diseaseāfree survival were 121.45 months and 93.03 months, respectively. The mean followāup interval was 41.0 months, and at the time of data analysis three patients had recurrent tumors. Seven (36.8%) patients experienced a major complication in the perioperative period; there were no perioperative mortalities. Orbit invasion was observed in four patients, with optic nerve impingement in 11 patients. Of these, three patients had longāterm diplopia. No patients experienced worsening of preoperative visual acuity. Conclusions: Olfactory groove meningiomas demonstrate a propensity to spread into the paranasal sinuses, particularly in recurrent cases. Given a tendency for infiltrative recurrence along the skull base, this disease represents an important area of collaboration between neurosurgery and otolaryngology. The subcranial approach offers excellent surgical access for excision, particularly for recurrences that involve the paranasal sinuses and optic apparatus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87044/1/22174_ftp.pd
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