3,424 research outputs found
The Synthesis of Poly(Propylene Fumarate)
Poly(propylene fumarate) is a promising material in the field of bone tissue engineering. A recently described chain growth polymerization was developed for the synthesis of poly(propylene fumarate). This pathway uses the ring-opening polymerization of maleic anhydride and propylene oxide with magnesium ethoxide as an initiator to yield poly(propylene maleate). The poly(propylene maleate) was then isomerized to poly(propylene fumarate) using diethyl amine. In order to scale up the reaction to a 20L reactor, several optimizations of the purification schemes was required. The main optimizations were done to the purification of poly(propylene maleate). Several methods were tested including replacing the water washes with brine washes, distillation to remove the remaining maleic anhydride, and the precipitation in diethyl ether. The diethyl ether precipitation method was significantly faster than the other methods and able to successfully remove the maleic anhydride. For these reasons the precipitation method was chosen for the purification of the poly(propylene maleate). The next step will be to attempt to improve the purification of poly(propylene fumarate). Once this is completed, the reaction will be ready for implementation at the 20 L batch reactor scale
Hybrid gold single crystals incorporating amino acids
Composite hybrid gold crystals are of profound interest in various research
areas ranging from materials science to biology. Their importance is due to
their unique properties and potential implementation, for example in sensing or
in bio-nanomedicine. Here we report on the formation of hybrid organic-metal
composites via the incorporation of selected amino acids histidine, aspartic
acid, serine, glutamine, alanine, cysteine, and selenocystine into the crystal
lattice of single crystals of gold. We used electron microscopy, chemical
analysis and high-resolution synchrotron powder X ray diffraction to examine
these composites. Crystal shape, as well as atomic concentrations of occluded
amino acids and their impact on the crystal structure of gold, were determined.
Concentration of the incorporated amino acid was highest for cysteine, followed
by serine and aspartic acid. Our results indicate that the incorporation
process probably occurs through a complex interaction of their individual
functional groups with gold atoms. Although various organic gold composites
have been prepared, to the best of our knowledge this is the first reported
finding of incorporation of organic molecules within the gold lattice. We
present a versatile strategy for fabricating crystalline nanohybrid composite
gold crystals of potential importance for a wide range of applications
Variable temperature study of the crystal and magnetic structures of the giant magnetoresistant materials LMnAsO (L=La, Nd)
Peer reviewedPublisher PD
Evidence of a structural anomaly at 14 K in polymerised CsC60
We report the results of a high-resolution synchrotron X-ray powder
diffraction study of polymerised CsC in the temperature range 4 to 40 K.
Its crystal structure is monoclinic (space group I2/m), isostructural with
RbC. Below 14 K, a spontaneous thermal contraction is observed along
both the polymer chain axis, and the interchain separation along [111],
. This structural anomaly could trigger the occurrence of the spin-singlet
ground state, observed by NMR at the same temperature.Comment: 8 pages, 5 figures, submitte
Bootstrapping navigation and path planning using human positional traces
Navigating and path planning in environments with limited a priori knowledge is a fundamental challenge for mobile robots. Robots operating in human-occupied environments must also respect sociocontextual boundaries such as personal workspaces. There is a need for robots to be able to navigate in such environments without having to explore and build an intricate representation of the world. In this paper, a method for supplementing directly observed environmental information with indirect observations of occupied space is presented. The proposed approach enables the online inclusion of novel human positional traces and environment information into a probabilistic framework for path planning. Encapsulation of sociocontextual information, such as identifying areas that people tend to use to move through the environment, is inherently achieved without supervised learning or labelling. Our method bootstraps navigation with indirectly observed sensor data, and leverages the flexibility of the Gaussian process (GP) for producing a navigational map that sampling based path planers such as Probabilistic Roadmaps (PRM) can effectively utilise. Empirical results on a mobile platform demonstrate that a robot can efficiently and socially-appropriately reach a desired goal by exploiting the navigational map in our Bayesian statistical framework. © 2013 IEEE
A comparison between conventional and LANDSAT based hydrologic modeling: The Four Mile Run case study
Models designed to support the hydrologic studies associated with urban water resources planning require input parameters that are defined in terms of land cover. Estimating the land cover is a difficult and expensive task when drainage areas larger than a few sq. km are involved. Conventional and LANDSAT based methods for estimating the land cover based input parameters required by hydrologic planning models were compared in a case study of the 50.5 sq. km (19.5 sq. mi) Four Mile Run Watershed in Virginia. Results of the study indicate that the LANDSAT based approach is highly cost effective for planning model studies. The conventional approach to define inputs was based on 1:3600 aerial photos, required 110 man-days and a total cost of 2,350. The conventional and LANDSAT based models gave similar results relative to discharges and estimated annual damages expected from no flood control, channelization, and detention storage alternatives
Spin-driven Phase Transitions in ZnCrSe and ZnCrS Probed by High Resolution Synchrotron X-ray and Neutron Powder Diffraction
The crystal and magnetic structures of the spinel compounds ZnCrS and
ZnCrSe were investigated by high resolution powder synchrotron and
neutron diffraction. ZnCrSe exhibits a first order phase transition at
K into an incommensurate helical magnetic structure. Magnetic
fluctuations above are coupled to the crystal lattice as manifested by
negative thermal expansion. Both, the complex magnetic structure and the
anomalous structural behavior can be related to magnetic frustration.
Application of an external magnetic field shifts the ordering temperature and
the regime of negative thermal expansion towards lower temperatures. Thereby,
the spin ordering changes into a conical structure. ZnCrS shows two
magnetic transitions at K and K that are accompanied by
structural phase transitions. The crystal structure transforms from the cubic
spinel-type (space group \={3}) at high temperatures in the paramagnetic
state, via a tetragonally distorted intermediate phase (space group /
) for into a low temperature orthorhombic phase
(space group ) for . The cooperative displacement of
sulfur ions by exchange striction is the origin of these structural phase
transitions. The low temperature structure of ZnCrS is identical to the
orthorhombic structure of magnetite below the Verwey transition. When applying
a magnetic field of 5 T the system shows an induced negative thermal expansion
in the intermediate magnetic phase as observed in ZnCrSe.Comment: 11 pages, 13 figures, to be published in PR
- …