Sustained fluvial deposition recorded in Mars' Noachian stratigraphic record.

Orbital observation has revealed a rich record of fluvial landforms on Mars, with much of this record dating 3.6-3.0 Ga. Despite widespread geomorphic evidence, few analyses of Mars' alluvial sedimentary-stratigraphic record exist, with detailed studies of alluvium largely limited to smaller sand-bodies amenable to study in-situ by rovers. These typically metre-scale outcrop dimensions have prevented interpretation of larger scale channel-morphology and long-term basin evolution, vital for understanding the past Martian climate. Here we give an interpretation of a large sedimentary succession at Izola mensa within the NW Hellas Basin rim. The succession comprises channel and barform packages which together demonstrate that river deposition was already well established >3.7 Ga. The deposits mirror terrestrial analogues subject to low-peak discharge variation, implying that river deposition at Izola was subject to sustained, potentially perennial, fluvial flow. Such conditions would require an environment capable of maintaining large volumes of water for extensive time-periods, necessitating a precipitation-driven hydrological cycle.

A Diverse Array of Fluvial Depositional Systems in Arabia Terra: Evidence for mid-Noachian to Early Hesperian Rivers on Mars.

Branching to sinuous ridges systems, hundreds of kilometers in length and comprising layered strata, are present across much of Arabia Terra, Mars. These ridges are interpreted as depositional fluvial channels, now preserved as inverted topography. Here we use high-resolution image and topographic data sets to investigate the morphology of these depositional systems and show key examples of their relationships to associated fluvial landforms. The inverted channel systems likely comprise indurated conglomerate, sandstone, and mudstone bodies, which form a multistory channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, which we interpret as paleolake deposits. Some inverted channels are located within erosional valley networks, which have regional and local catchments. Inverted channels are typically found in downslope sections of valley networks, sometimes at the margins of basins, and numerous different transition morphologies are observed. These relationships indicate a complex history of erosion and deposition, possibly controlled by changes in water or sediment flux, or base-level variation. Other inverted channel systems have no clear preserved catchment, likely lost due to regional resurfacing of upland areas. Sediment may have been transported through Arabia Terra toward the dichotomy and stored in local and regional-scale basins. Regional stratigraphic relations suggest these systems were active between the mid-Noachian and early Hesperian. The morphology of these systems is supportive of an early Mars climate, which was characterized by prolonged precipitation and runoff.

Persistence of intense, climate-driven runoff late in Mars history.

Mars is dry today, but numerous precipitation-fed paleo-rivers are found across the planet's surface. These rivers' existence is a challenge to models of planetary climate evolution. We report results indicating that, for a given catchment area, rivers on Mars were wider than rivers on Earth today. We use the scale (width and wavelength) of Mars paleo-rivers as a proxy for past runoff production. Using multiple methods, we infer that intense runoff production of >(3-20) kg/m2 per day persisted until <3 billion years (Ga) ago and probably <1 Ga ago, and was globally distributed. Therefore, the intense runoff production inferred from the results of the Mars Science Laboratory rover was not a short-lived or local anomaly. Rather, precipitation-fed runoff production was globally distributed, was intense, and persisted intermittently over >1 Ga. Our improved history of Mars' river runoff places new constraints on the unknown mechanism that caused wet climates on Mars.

Melanotic neuroectodermal tumor of infancy: a wolf in sheep's clothing.

INTRODUCTION: The melanotic neuroectodermal tumor of infancy (MNTI) is an exceptionally rare neoplasm. Despite their potential for local invasion, MNTI are considered benign neoplasms. Sporadic cases have been reported of MNTI acting in a malignant fashion; however, the majority of these tumors were of extragnathic origin. METHODS: A 2-month-old male presented with a rapidly expanding maxillary mass. The patient underwent excisional biopsy of the mass and a diagnosis of MNTI was returned. Tumor recurrence was appreciated postoperatively. Neoadjuvant chemotherapy was initiated to render it more amenable to surgical resection. Chemotherapy was suspended prematurely and the patient returned to the operating room for hemimaxillectomy. The postchemotherapy surgical pathology report demonstrated a unique mixed chemotherapy response. DISCUSSION: This report highlights the aggressive nature of gnathic MNTI, the importance of early diagnosis and definitive intervention, and the mixed clinical and histologic response of the lesion to neoadjuvant chemotherapy.

Demand for single- and dual-degree oral and maxillofacial surgery residency positions.

PURPOSE: Currently, no consensus has been reached regarding which track, single- or dual-degree, better prepares a resident for oral and maxillofacial surgery (OMS) practice. It is doubtful that such a consensus will ever exist. The purpose of the present study was to explore the trends in the selection of, and competition for, single- and dual-degree residency positions, with the ultimate goal of determining which degree track is in greater demand among recent applicants. MATERIALS AND METHODS: National match statistics were obtained from the American Association of Oral and Maxillofacial Surgeons. Data were drawn from each annual residency match for 1986-1987 through 2009-2010. For each match year, the data included the total number of OMS residency applicants participating in the National Matching Service, the total number of OMS positions offered, and the number of single- and dual-degree OMS positions that had been successfully matched. A piecewise regression analysis was used to evaluate the trends in the data. RESULTS: During the 1996-1997 to 2009-2010 period, both the preference for single- and dual-degree positions and the proportion of single- and dual-degree positions offered remained relatively constant. On average, 50.19% ± 2.27% of applicants preferred single-degree positions, 24.44% ± 2.42% preferred dual-degree positions, and 25.70% ± 2.27% had no preference. The demand for each single-degree position from 1996-1997 to 2009-2010 was 1.44 times greater than that for each dual-degree position (P < .0001). CONCLUSIONS: The proportions of single- and dual-degree OMS residency positions and applicant preference for a single- or dual-degree position have remained relatively constant during the past 14 match years. Recent trends have suggested a significantly greater demand for the single- versus dual-degree OMS residency position.

Bone healing with an in situ-formed bioresorbable polyethylene glycol hydrogel membrane in rabbit calvarial defects.

OBJECTIVES: The aims of this study were to test whether or not the application of an in situ-formed synthetic polyethylene glycol hydrogel (PEG) used as a biodegradable membrane for guided bone regeneration with a variety of graft materials and ambient oxygen or hyperbaric oxygen (HBO) environments would result in enhanced bone regeneration, and to observe the histologic and histomorphometric aspects of bone healing of the calvarial defects with and without a PEG membrane. STUDY DESIGN: Thirty adult, skeletally mature, male New Zealand white rabbits were randomly divided into 3 groups of 10 animals each. Bilateral 15-mm-diameter critical-size defects were created in the parietal bones of each animal. Group 1 served as a control with unfilled bilateral calvarial defects, group 2 had bilateral calvarial defects filled with morcelized autogenous calvarial bone, and group 3 had bilateral calvarial defects filled with a biphasic calcium phosphate ceramic. One of the calvarial defects was randomly protected with a PEG resorbable liquid membrane in each animal. Five animals from each group underwent a course of HBO treatment (2.4 ATA 100% oxygen for 90 minutes 5 days a week for 4 weeks) and the other 5 served as control and did not receive any supplemental oxygen (normobaric). The animals were killed 6 weeks after their surgery, and their parietal bones were harvested. The specimens were analyzed with microscopic computerized tomography (microCT) scans and histomorphometrics. RESULTS: The unfilled normobaric control bony defects did not heal, proving the critical-size nature of these defects. The presence of autogenous bone or bone ceramic in the defects increased the bone volume fraction and bone mineral density of the defects (P < .001). The presence of a membrane in the ungrafted and autogenous bone grafted defects resulted in a decrease in the corrected bone volume fraction (P = .002) but not in the bone ceramic grafted defects (P = .580). Bony healing of defects where the membrane was unsupported was compromised; the membrane did not maintain the desired bone regeneration volume with the unfilled and autogenous bone grafted groups. The PEG resorbable liquid membrane worked best with the bone ceramic material. HBO did not ameliorate the healing of the autogenous bone graft or ceramic filled defects in the 6-week time period of this study. CONCLUSIONS: Although the PEG resorbable liquid membrane is easy to use and forms an occlusive layer, caution is recommended when using the membrane over an unsupported defect. HBO did not ameliorate bony healing with the membrane at the early 6-week time point. The authors recommend future assessment with HBO at the 12-week time point.