Controlling the electronic structure of bilayer graphene

We describe the synthesis of bilayer graphene thin films deposited on insulating silicon carbide and report the characterization of their electronic band structure using angle-resolved photoemission. By selectively adjusting the carrier concentration in each layer, changes in the Coulomb potential led to control of the gap between valence and conduction bands. This control over the band structure suggests the potential application of bilayer graphene to switching functions in atomic-scale electronic devices.     

Recent history of sediment deposition in marl- and sand-based marshes of Belize, Central America

There are two contrasting types of wetlands in Belize: marl- and sand-based marshes. We measured accumulation rates of sediment in six cores from marl- and sand-based marshes of northern Belize and compared biogeochemical characteristics to assess recent wetland history (1850 to present). Sediment depth increments were analysed for bulk density, LOI, nutrients (C, N, P, S, Ca, Mg, K and Na) and snail shell density and species diversity. Cores were dated using ²¹⁰Pb and a constant rate of supply model. Unsupported ²¹⁰Pb inventories of the cores ranged from 6.16 to 8.92 pCi cm⁻². Marl-based marshes showed the maximum peak of ²¹⁰Pb activity from 4 to 10 cm below the sediment surface. ²¹⁰Pb peaks corresponded with the bottom of a marl layer containing chlorophyll a and we suggest that this relationship reflects the high growth and decomposition rates of cyanobacterial mat. Inorganic carbon, Ca, Mg, K, Na, S and Pb contents and accumulation rates were much greater in the marl-based marshes than in the sand-based marshes. Average dry mass accumulation rates in the six marshes ranged from 113 to 572 g m⁻² year⁻¹ over the past 100 years. Average linear sedimentation rates during the last 100 years in the two types were not significantly different (0.93 and 1.08 mm year⁻¹, respectively). Increased sediment accumulation by human activities such as soil washout from adjacent roads was recorded in a sand-based marsh near roads. Sediment cores in the marl-based marshes display changes of marsh vegetation, apparently caused by water level changes. The vegetation change occurred at the end of the 1800s and the beginning of 1900s and is represented by a band of dark peat in otherwise marl-dominated sediments. Overall, the sediment cores show that conditions were relatively undisturbed by human activities in the recent past.     

Metabolism and morphology of brown adipose tissue from Brahman and Angus newborn calves

The objective of this study was to compare adipocyte morphology and lipogenesis between breed types (Angus vs Brahman) in brown adipose tissue (BAT) and white adipose tissue (WAT) from newborn calves. The Brahman calves (n = 7) were born during the fall season, whereas the Angus calves were born in fall (n = 6) or the following spring (n = 4). At parturition, Brahman cows were lighter than fall Angus cows, but were heavier than spring Angus cows (P < .05). Birth weights and perirenal BAT weights were greater in spring-born, but not in fall-born Angus calves, than in Brahman calves (P < .05). Fall-born Angus BAT contained 63% more (P < .05) adipocytes/100 mg tissue and contained a greater proportion (P < .05) of adipocytes with mean diameters of 40 to 50 microm, and fewer adipocytes with diameters of 60 microm or greater, than Brahman BAT. Brahman BAT contained two-to-three times as many beta-receptors as Angus BAT (P < .05), although the dissociation constant (Kd) was not different between breed types. Mitochondria in Brahman BAT were primarily spherical, whereas Angus BAT mitochondria were elongated, and mitochondrial cross-sectional area tended (P = .08) to be greater in Brahman BAT than in Angus BAT. The mitochondrial uncoupling protein (UCP) mRNA concentration (per 10(6) cells) was greater in Brahman BAT than in BAT from fall-born Angus calves. Lipogenesis from acetate was greater in Angus BAT than in Brahman BAT (P < .05), and glucose and palmitate contributed a greater proportion of carbon to lipogenesis in Brahman BAT than in Angus BAT. These differences in lipogenesis between breed types were not observed in s.c. WAT. The WAT from both breed types contained adipocytes with distinct brown adipocyte morphology, suggesting an involution of BAT to WAT in utero. We conclude that differences in UCP gene expression cannot cause the greater peak thermogenesis of Angus calves; however, differences between breed types in lipid metabolism and(or) mitochondrial morphology may contribute to this phenomenon.     

Radiographic findings and clinical factors in dogs with surgically confirmed or presumed colonic torsion

Colonic torsion is a life‐threatening condition in dogs and radiographic findings for this condition have not been well described. The purpose of this retrospective case series was to describe radiographic findings and clinical signs in a group of dogs with colonic torsion. Inclusion criteria were dogs presenting during the period of 2006 and 2016, and that had abdominal radiography and a surgically confirmed or presumed diagnosis of colonic torsion. For each dog, clinical data were recorded from medical records and imaging findings were recorded from retrieved plain radiographs and positive contrast radiographs in which barium enema was performed. Fourteen dogs met inclusion criteria. Of these, nine dogs had colonic torsion confirmed at surgery, with five dogs having surgical confirmation of colonic congestion or mesenteric torsion. Radiographic findings included segmental distention of the colon (14/14), focal narrowing of the colon (11/14), displacement of cecum (11/14), displacement of descending colon (14/14), and mild to no small intestinal distention (14/14). In cases where barium enema was performed, focal narrowing of the colon and longitudinal striations that course in a helical pattern were identified, termed the “torsion sign.” Vomiting was the most common clinical sign observed (12/14), followed by abdominal pain in a small majority of cases (8/14). Severe abdominal pain and hypovolemic shock were uncommon in the patients reported (3/14). Colonic torsion should be considered as a differential diagnosis for dogs with radiographic segmental colonic distention with displacement of the descending colon and cecum. Barium enema is recommended for more definitive diagnosis.