156 research outputs found
Temperature-dependent 2D-3D growth transition of ultra-thin Pt films deposited by PLD
During the growth of metal thin films on dielectric substrates at a given
deposition temperature T, the film's morphology is conditioned by the magnitude
and asymmetry of up- and downhill diffusion. Any severe change of this
mechanism leads to a growth instability, which induces an alteration of the
thin film morphology. In order to study this mechanism, ultra-thin Pt films
were deposited via pulsed laser deposition (PLD) onto
yttria-stabilized-zirconia single crystals at different deposition
temperatures. The morphological evolution of Pt thin films has been
investigated by means of scanning electron microscopy (SEM), atomic force
microscopy (AFM) and standard image analysis techniques. The experimentally
obtained morphologies are compared to simulated thin film structures resulting
from a two-dimensional kinetic Monte Carlo (KMC) approach. Two main
observations have been made: i) Thin Pt films deposited onto zirconia undergo a
growth transition from two-dimensional to three-dimensional growth at T > 573
K. The growth transition and related morphological changes are a function of
the deposition temperature. ii) A critical cluster size of i\ast = 4 in
combination with an asymmetric Ehrlich-Schwoebel (ES) barrier favoring the
uphill diffusion of atoms allows for a computational reproduction of the
experimentally obtained film morphologies.Comment: 7 pages, 6 figures, 1 tabl
Effect of deposition rate on morphology evolution of metal-on-insulator films grown by pulsed laser deposition
Metacarpal Neck Fractures: A Review of Surgical Indications and Techniques
Context: Hand injuries are a common emergency department presentation. Metacarpal fractures account for 40% of all hand fractures and can be seen in the setting of low or high energy trauma. The most common injury pattern is a metacarpal neck fracture. In this study, the authors aim to review the surgical indications for metacarpal neck fractures, the fixation options available along with the risk and benefits of each.
Evidence Acquisition: Literature review of the different treatment modalities for metacarpal neck fractures. Review focuses on surgical indications and the risks and benefits of different operative techniques.
Results: The indications for surgery are based on the amount of dorsal angulation of the distal fragment. The ulnar digits can tolerate greater angulation as the radial digits more easily lose grip strength. The most widely utilized fixation techniques are pinning with k-wires, dorsal plating, or intramedullary fixation. There is currently no consensus on an optimal fixation technique as surgical management has been found to have a complication rate up to 36%. Plate and screw fixation demonstrated especially high complication rates.
Conclusions: Metacarpal neck fractures are a common injury in young and active patients that results in substantial missed time from work. While the surgical indications are well-described, there is no consensus on the optimal treatment modality because of high complication rates. Dorsal plating has higher complication rates than closed reduction and percutaneous pinning, but is necessary in comminuted fractures. The lack of an ideal fixation construct suggests that further study of the commonly utilized techniques as well as novel techniques is necessary
Possible control of acute outbreaks of a marine fungal pathogen by nominally herbivorous tropical reef fish
Phosphatidylcholine fatty acid membranes: Effects of headgroup hydration on the phase behaviour and structural parameters of the gel and inverse hexagonal (H-II) phases
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Comparison of Structure and Properties of Femtosecond and Nanosecond Laser-Structured Silicon
We compare the optical properties, chemical composition, and crystallinity of silicon microstructures formed in the presence of SF6 by femtosecond laser irradiation and by nanosecond laser irradiation. In spite of very different morphology and crystallinity, the optical properties and chemical composition of the two types of microstructures are very similar. The structures formed with femtosecond (fs) pulses are covered with a disordered nanocrystalline surface layer less than 1 um thick, while those formed with nanosecond (ns) pulses have very little disorder. Both ns-laser-formed and fs-laser-formed structures absorb near-infrared (1.1 ā 2.5 um) radiation strongly and have roughly 0.5% sulfur impurities.Engineering and Applied Science
Comparison Of Structure And Properties Of Femtosecond And Nanosecond Laser-Structured Silicon
We compare the optical properties,chemical composition, and crystallinity of siliconmicrostructures formed in the presence of SF6 by femtosecond laserirradiation and by nanosecond laser irradiation. In spite of very different morphology and crystallinity, the optical properties and chemical composition of the two types of microstructures are very similar. The structures formed with femtosecond (fs) pulses are covered with a disordered nanocrystalline surface layer less than 1 Ī¼m thick, while those formed with nanosecond (ns) pulses have very little disorder. Both ns-laser-formed and fs-laser-formed structures absorb near-infrared (1.1ā2.5āĪ¼m) radiation strongly and have roughly 0.5% sulfur impurities
Fabrication and subband gap optical properties of silicon supersaturated with chalcogens by ion implantation and pulsed laser melting
Topographically flat, single crystal silicon supersaturated with the chalcogens S, Se, and Te was prepared by ion implantation followed by pulsed laser melting and rapid solidification. The influences of the number of laser shots on the atomic and carrier concentration-depth profiles were measured with secondary ion mass spectrometry and spreading resistance profiling, respectively. We found good agreement between the atomic concentration-depth profiles obtained from experiments and a one-dimensional model for plane-front melting, solidification, liquid-phase diffusion, with kinetic solute trapping, and surface evaporation. Broadband subband gap absorption is exhibited by all dopants over a wavelength range from 1 to 2.5 microns. The absorption did not change appreciably with increasing number of laser shots, despite a measurable loss of chalcogen and of electronic carriers after each shot.One
of the authors M.T. acknowledges the financial support of
the Fulbright Program. This research was supported in part
by the U.S. Army ARDEC under Contract No. W15QKN-07-
P-0092
Analysis of a consumer survey on plug-in hybrid electric vehicles
Plug-in Hybrid Electric Vehicles (PHEVs) show potential to reduce greenhouse gas (GHG) emissions, increase fuel efficiency, and offer driving ranges that are not limited by battery capacity. However, these benefits will not be realized if consumers do not adopt this new technology. Several agent-based models have been developed to model potential market penetration of PHEVs, but gaps in the available data limit the usefulness of these models. To address this, we administered a survey to 1000 stated US residents, using Amazon Mechanical Turk, to better understand factors influencing the potential for PHEV market penetration. Our analysis of the survey results reveals quantitative patterns and correlations that extend the existing literature. For example, respondents who felt most strongly about reducing US transportation energy consumption and cutting greenhouse gas emissions had, respectively, 71 and 44 times greater odds of saying they would consider purchasing a compact PHEV than those who felt least strongly about these issues. However, even the most inclined to consider a compact PHEV were not generally willing to pay more than a few thousand US dollars extra for the sticker price. Consistent with prior research, we found that financial and battery-related concerns remain major obstacles to widespread PHEV market penetration. We discuss how our results help to inform agent-based models of PHEV market penetration, governmental policies, and manufacturer pricing and marketing strategies to promote consumer adoption of PHEVs. Ā© 2014 The Authors
Supersaturating silicon with transition metals by ion implantation and pulsed laser melting
We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v D, of Au and Zn, and put lower bounds on v D of the other metals ranging from 10Ā² to 10ā“ām/s. Knowledge of v D is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10Ā¹ā¹ Au/cmĀ³ without cellular breakdown. Values of v D are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D s(T m), and the equilibrium partition coefficient, k e, are shown to simultaneously affect v D. We demonstrate a correlation between v D and the ratio D s(T m)/k e ā°Ā·ā¶ā·, which is exhibited for Group III, IV, and V solutes but not for the transition metals investigated. Nevertheless, comparison with experimental results suggests that D s(T m)/k e ā°Ā·ā¶ā· might serve as a metric for evaluating the potential to supersaturate Si with transition metals by PLM.Research at Harvard was supported by The U.S. Army
Research Office under contracts W911NF-12-1-0196 and
W911NF-09-1-0118. M.T.W. and T.B.ās work was supported
by the U.S. Army Research Laboratory and the U.S.
Army Research Office under Grant No. W911NF-10-1-0442,
and the National Science Foundation (NSF) Faculty Early
Career Development Program ECCS-1150878 (to T.B.).
M.J.S., J.T.S., M.T.W., T.B., and S.G. acknowledge a generous
gift from the Chesonis Family Foundation and support in
part by the National Science Foundation (NSF) and the
Department of Energy (DOE) under NSF CA No. EEC-
1041895. S.C. and J.S.W.ās work was supported by The
Australian Research Council. J.M. was supported by a
National Research Council Research Associateship
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