Lost and found dark matter in elliptical galaxies.

There is strong evidence that the mass of the Universe is dominated by dark matter, which exerts gravitational attraction but whose exact nature is unknown. In particular, all galaxies are believed to be embedded in massive haloes of dark matter. This view has recently been challenged by the observation of surprisingly low random stellar velocities in the outskirts of ordinary elliptical galaxies, which has been interpreted as indicating a lack of dark matter. Here we show that the low velocities are in fact compatible with galaxy formation in dark-matter haloes. Using numerical simulations of disk-galaxy mergers, we find that the stellar orbits in the outer regions of the resulting ellipticals are very elongated. These stars were torn by tidal forces from their original galaxies during the first close passage and put on outgoing trajectories. The elongated orbits, combined with the steeply falling density profile of the observed tracers, explain the observed low velocities even in the presence of large amounts of dark matter. Projection effects when viewing a triaxial elliptical can lead to even lower observed velocities along certain lines of sight.

Amniotic membrane inlay and overlay grafting for corneal epithelial defects and stromal ulcers.

OBJECTIVES: To determine the effect of amniotic membrane transplantation (AMT) on persistent corneal epithelial defects (PEDs) and to compare the efficacy between inlay and overlay techniques. METHODS: Thirty patients (30 eyes) underwent AMT for PED. The use of AMT was restricted to patients in whom all previous measures, including bandage contact lens and tarsorrhaphy, had failed. The amniotic membrane was placed on the surface of the cornea in overlay (group A) or inlay (group B) fashion. RESULTS: The PED healed after the first AMT in 21 eyes (70%) within an average of 25.5 days after surgery and recurred in 6 eyes (29%). Among the 22 eyes treated with an overlay AMT (group A), the PED healed after the first AMT in 14 eyes (64%) within an average of 24.5 days and recurred in 4 eyes (29%). Among the 8 eyes treated with an inlay AMT (group B), the PED healed within an average of 27.4 days after AMT, which did not statistically significantly differ from group A (P = .72). The PED healed after the first AMT in 7 eyes (88%) and recurred in 2 (29%) of 7 eyes. CONCLUSIONS: The AMT can be helpful in the treatment of PED in which all other conventional management has failed. However, the success rate in our study was not as high as that previously reported, and our results showed a high incidence of recurrences of epithelial defects. We did not find any difference between overlay and inlay techniques in terms of healing time and recurrence rate.

Cosmic questions: an introduction.

This introductory talk at the Cosmic Questions conference sponsored by the AAAS summarizes some earlier pictures of the universe and some pictures based on modern physics and cosmology. The uroboros (snake swallowing its tail) is an example of a traditional picture. The Biblical flat-earth picture was very different from the Greek spherical earth-centered picture, which was the standard view until the end of the Middle Ages. Many people incorrectly assume that the Newtonian picture of stars scattered through otherwise empty space is still the prevailing view. Seeing Earth from space shows the power of a new picture. The Hubble Space Telescope can see all the bright galaxies, all the way to the cosmic Dark Ages. We are at the center of cosmic spheres of time: looking outward is looking backward in time. All the matter and energy in the universe can be represented as a cosmic density pyramid. The laws of physics only allow the material objects in the universe to occupy a wedge-shaped region on a diagram of mass versus size. All sizes--from the smallest size scale, the Planck scale, to the entire visible universe--can be represented on the Cosmic Uroboros. There are interesting connections across this diagram, and the human scale lies in the middle.

Theoretical analysis of ablation depths and profiles in laser in situ keratomileusis for compound hyperopic and mixed astigmatism.

PURPOSE: To compare the theoretical ablation depths and profiles of 4 treatment strategies for compound hyperopic and mixed astigmatism. SETTING: Theoretical analysis. METHODS: Corneal contour drawings of theoretical corneal ablation profiles during laser in situ keratomileusis (LASIK) and photoastigmatic refractive keratectomy were made. The depths of tissue ablation in 4 treatment strategies for compound hyperopic astigmatism (Groups 1 to 4) and for mixed astigmatism (Groups 5 to 8) were compared: (1) combined hyperopic spherical and myopic cylindrical treatments (Groups 1 and 5); (2) combined spherical and hyperopic cylindrical treatments (Groups 2 and 6); (3) combined cylindrical treatments (Groups 3 and 7); (4) combined cross-cylinder and spherical equivalent treatments (Groups 4 and 8). RESULTS: In compound hyperopic astigmatism, the 4 approaches resulted in identical final curvatures, but the ablation depths were greatest in Group 1 (combined hyperopic spherical and myopic cylindrical treatments). The smallest amount of ablation occurred in Group 2 (combined hyperopic spherical and hyperopic cylindrical treatments) and Group 3 (combined hyperopic cylindrical treatments), which had similar tissue ablation patterns. In mixed astigmatism, the greatest ablation depth was in Group 5, followed by Group 8, and Groups 6 and 7. The tissue ablation depths and profiles were similar in Groups 6 and 7. CONCLUSION: The treatment approaches in Groups 2, 3, 6, and 7 (which avoided the use of minus cylinder) resulted in the smallest degree of stromal ablation. Patients with compound hyperopic or mixed astigmatism may benefit from reduced ablation depths by deferring treatment until hyperopic cylindrical and/or combined cylindrical treatments are available.

Visual recovery after a year of craniopharyngioma-related amaurosis: report of a nine-year-old child and a review of pathophysiologic mechanisms.

BACKGROUND: The probability of visual recovery in tumor-related optic neuropathy usually correlates with the severity and duration of optic pathway compromise. Recovery of visual acuity to normal levels is unexpected after profound loss of vision extending for a period of weeks and months. METHODS: A 9-year-old girl who had neurosurgical resection of a craniopharyngioma compressing the optic chiasm and optic tract was followed up serially with neuroimaging and clinical examinations over a 6-year period. RESULTS: Within 3 months of the diagnosis of craniopharyngioma, the girl's vision was reduced to no-light-perception blindness when she viewed with the more involved eye. The blindness correlated with an amaurotic (i.e., >3.6 log unit) relative afferent pupillary defect and an absence of any response when tested with visual field perimetry. After more than a year of total blindness and cessation of all neurosurgical and radiation therapy, visual acuity recovered to a normal level (20/25), the afferent pupillary defect improved, and sensitivity in a portion of the temporal hemivisual field was restored. In the follow-up that has extended for 5 years from the time of recovery, stability of the restored vision has been documented. CONCLUSION: Children who have tumor-related loss of vision due to damage to the anterior visual pathways may be capable of recovery after intervals of blindness that would be considered irreversible in adults. The mechanism of the recovery in our patient may have been decompression-related restoration of axoplasmic flow, followed by gradual remyelination of visual fibers, which allowed reorganization of connections to the lateral geniculate nucleus to optimize synaptic transmission.

Tuberculin skin testing of hospitalized patients.

OBJECTIVES: We sought to define the prevalence of tuberculin skin test (TST) positivity in a group of newly hospitalized patients, to identify risk factors for positive tests, and to examine the impact of testing on infection control practices. DESIGN: Unblinded cohort study over 5 days in July 1992. SETTING: A 1,000-bed university-affiliated hospital. PATIENTS: All patients admitted (excluding obstetric patients and newborns) were interviewed. Patients without a history of tuberculosis (TB) or a positive TST were offered a TST with Candida and tetanus controls. RESULTS: Of 346 patients offered the test, 21 (6%) had a prior history of TB or a positive TST, and 36 (10%) declined to participate; 279 of the remaining 289 completed the study. Anergy was demonstrated in 94 (33.7%) of 279 patients. New positive TSTs were identified in 19 (10.3%) of 185 nonanergic patients. Of the 19 TST-positive patients, 6 (32%) had infiltrates on chest radiographs and were evaluated for active TB. One patient was treated empirically for active TB, and five received isoniazid prophylaxis. Risk factors for a new positive TST included age (odds ratio [OR], 1.56 per decade of life; P = .021), African American race (OR, 4.81; P = .008), alcohol abuse (OR, 5.53; P = .005), and peptic ulcer disease (OR, 4.53; P = .017). Risk factors for anergy included admission to a surgical service (OR, 2.1; P = .006), current use of steroids (OR, 2.65; P = .005), and human immunodeficiency virus (HIV) infection (OR, undefined; P = .034). CONCLUSIONS: Despite a high rate of anergy, routine tuberculin skin testing identified a substantial number of patients with TB infection who might otherwise have gone unrecognized.

Retinal detachment in a child as the first sign of leukemic relapse: histopathology, MRI findings, treatment, and tumor-free follow up.

Improved leukemia therapies in children have brought about prolonged remissions with extramedullary relapses being reported in sites other than the most common (bone marrow, testes, brain, and spinal cord). A 3-1/2 year-old boy with a history of acute lymphocytic leukemia presented with total retinal detachment in one eye. Painful glaucoma unresponsive to medical therapy necessitated enucleation. Histopathologic examination documented the presence of a dense leukemic cellular infiltrate replacing a totally detached, necrotic retina. Tumor cells also were present in the optic nerve. The child had remained free of leukemia for 3 years after systemic and intrathecal chemotherapy, supplemented by craniospinal radiation. This represents the first case of relapse of acute lymphocytic leukemia presenting solely as a retinal detachment. Our case also underscores the point that the treatment of leukemia after an isolated ocular relapse can be associated with a favorable outcome.

A molecular and carbon isotopic study towards the origin and diagenetic fate of diaromatic carotenoids.

Pyrolysates of high-molecular-weight sedimentary fractions of the Duvernay Formation (Western Canada Basin) are dominated by 1,2,3,4- and 1,2,3,5-tetramethylbenzene, which, generated via beta-cleavage, indicate the presence of diaromatic carotenoids in the macromolecular aggregates. This was substantiated by desulphurization of sulphur-rich aggregates of the polar fraction, which released (partly) hydrogenated carotenoids. Furthermore, these components were important constituents of the aromatic hydrocarbon fractions and related oils. Apart from renieratane and isorenieratane, 1H NMR analysis established the aromatic substitution pattern of the most abundant component present, which was identified as a diaromatic compound with an unprecedented 2,3,6-/3,4,5-trimethyl aromatic substitution pattern. Molecular and isotopic analyses of both soluble and insoluble fractions of organic matter revealed relationships between diagenetically-derived carotenoids found in bitumen and related oils and their precursors incorporated into high-molecular-weight fractions. Aryl isoprenoids, important components in extracts and oils, were apparently derived from thermal cracking of bound diaromatic carotenoids rather than cleavage of free carotenoids as previously suggested. Furthermore, products derived from diaromatic carotenoids were substantially enriched in 13C relative to n-alkanes of algal origin. Together with the characteristic carotenoids, this isotopic enrichment provides evidence of significant contributions from photosynthetic green sulphur bacteria (Chlorobiaceae), which fix carbon via the reversed tricarboxylic acid (TCA) cycle. In spite of the prominence of these molecular signals, the overall isotopic composition of the organic matter indicated that only a very small portion of the preserved organic carbon was derived from the biomass of photosynthetic green sulphur bacteria.

Evaluation of rooms with negative pressure ventilation used for respiratory isolation in seven midwestern hospitals.

OBJECTIVE: To determine the number and efficacy of respiratory isolation facilities in St. Louis hospitals and to assess the mechanisms in place for evaluating function of hospital ventilation systems. DESIGN: A prospective multi-hospital surveillance study using direct observation and a standardized questionnaire. SETTING: Seven hospitals (including university-affiliated large teaching, private community, private teaching, and private nonteaching adult hospitals, and one pediatric teaching hospital) in St. Louis, Missouri. MEASUREMENTS: Actual direction of airflow in rooms designated for respiratory isolation was measured using smokesticks. Hospital demographic information, respiratory isolation policies, and frequency of ventilation tests were provided by infection control personnel. RESULTS: One hundred twenty-one (3.4%) of 3,574 hospital rooms were designed to have negative pressure ventilation suitable for respiratory isolation. The percentage of isolation rooms in each institution ranged from 0.4% (92 of 486) to 93% (39 of 42). Only three (43%) of seven hospitals had intensive care respiratory isolation rooms, and none had isolation rooms in the emergency department. No hospital had tested routinely the efficacy of the negative pressure ventilation, and two (28%) of seven had tested airflow for the first time in the past year. We tested 115 (95%) of 121 isolation rooms. With the doors closed, 52 (45%) of 115 designated negative pressure rooms actually had positive airflow to the corridor. The number of negative pressure rooms and the presence or absence of anterooms did not predict correct direction of airflow. There was a significant difference among hospitals in the percentage of designated isolation rooms that had truly negative pressure (P < 0.0001). Hospital age, size, and type correlated with correct direction of airflow (P < 0.0001). CONCLUSION: In the hospitals studied, only a small number of rooms were designated for respiratory isolation, and the performance of these was not tested routinely. High-risk areas including intensive care units and emergency rooms were not equipped to provide respiratory isolation. The direction of airflow in respiratory isolation rooms was not always correct and should be evaluated frequently.