3,590 research outputs found
Graphite Nanoeraser
We present here a method for cleaning intermediate-size (5~50nm)
contamination from highly oriented pyrolytic graphite. Electron beam deposition
causes a continuous increase of carbonaceous material on graphene and graphite
surfaces, which is difficult to remove by conventional techniques. Direct
mechanical wiping using a graphite nanoeraser is observed to drastically reduce
the amount of contamination. After the mechanical removal of contamination, the
graphite surfaces were able to self-retract after shearing, indicating that van
der Waals contact bonding is restored. Since contact bonding provides an
indication of a level of cleanliness normally only attainable in a high-quality
clean-room, we discuss potential applications in preparation of ultraclean
surfaces.Comment: 10 pages, two figure
Delivery Device and Method for Forming the Same
A delivery device includes a hollow container, and a plurality of biodegradable and/or erodible polymeric layers established in the container. A layer including a predetermined substance is established between each of the plurality of polymeric layers, whereby degradation of the polymeric layer and release of the predetermined substance occur intermittently. Methods for forming the device are also disclosed herein
Polymeric Scaffolds for Bone Tissue Engineering
Bone tissue engineering is a rapidly developing area. Engineering bone typically uses an artificial extracellular matrix (scaffold), osteoblasts or cells that can become osteoblasts, and regulating factors that promote cell attachment, differentiation, and mineralized bone formation. Among them, highly porous scaffolds play a critical role in cell seeding, proliferation, and new 3D-tissue formation. A variety of biodegradable polymer materials and scaffolding fabrication techniques for bone tissue engineering have been investigated over the past decade. This article reviews the polymer materials, scaffold design, and fabrication methods for bone tissue engineering. Advantages and limitations of these materials and methods are analyzed. Various architectural parameters of scaffolds important for bone tissue engineering (e.g. porosity, pore size, interconnectivity, and pore-wall microstructures) are discussed. Surface modification of scaffolds is also discussed based on the significant effect of surface chemistry on cells adhesion and function.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44003/1/10439_2004_Article_482175.pd
A note on spherically symmetric naked singularities in general dimension
We discuss generalizations of the recent theorem by Dafermos (hep-th/0403033)
forbidding a certain class of naked singularities in the spherical collapse of
a scalar field. Employing techniques similar to the ones Dafermos used, we
consider extending the theorem (1) to higher dimensions, (2) by including more
general matter represented by a stress-energy tensor satisfying certain
assumptions, and (3) by replacing the spherical geometry by a toroidal or
higher genus (locally hyperbolic) one. We show that the extension to higher
dimensions and a more general topology is straightforward; on the other hand,
replacing the scalar field by a more general matter content forces us to shrink
the class of naked singularities we are able to exclude. We then show that the
most common matter theories (scalar field interacting with a non-abelian gauge
field and a perfect fluid satisfying certain conditions) obey the assumptions
of our weaker theorem, and we end by commenting on the applicability of our
results to the five-dimensional AdS scenarii considered recently in the
literature.Comment: 16 pages, no figures, typos fixe
Hidden magnetic order in CuNCN
We report a comprehensive experimental and theoretical study of the
quasi-one-dimensional quantum magnet CuNCN. Based on magnetization measurements
above room temperature as well as muon spin rotation and electron spin
resonance measurements, we unequivocally establish the localized Cu+2-based
magnetism and the magnetic transition around 70 K, both controversially
discussed in the previous literature. Thermodynamic data conform to the
uniform-spin-chain model with a nearest-neighbor intrachain coupling of about
2300 K, in remarkable agreement with the microscopic magnetic model based on
density functional theory band-structure calculations. Using exact
diagonalization and the coupled-cluster method, we derive a collinear
antiferromagnetic order with a strongly reduced ordered moment of about 0.4
mu_B, indicating strong quantum fluctuations inherent to this
quasi-one-dimensional spin system. We re-analyze the available
neutron-scattering data, and conclude that they are not sufficient to resolve
or disprove the magnetic order in CuNCN. By contrast, spectroscopic techniques
indeed show signatures of long-range magnetic order below 70 K, yet with a
rather broad distribution of internal field probed by implanted muons. We
contemplate the possible structural origin of this effect and emphasize
peculiar features of the microstructure studied with synchrotron powder x-ray
diffraction.Comment: 17 pages, 17 figures, 1 tabl
Effect of H on the crystalline and magnetic structures of the YCo3-H(D) system. I. YCo3 from neutron powder diffraction and first-principles calculations
This paper reports investigations into the influence of hydrogen on the magnetic properties of the YCo3-H
system. We report results on the magnetic structure and magnetic transitions of YCo3 using a combination of
neutron powder diffraction measurements and first-principles full potential augmented plane wave + local
orbital calculations under the generalized gradient approximation. The ferromagnetic and ferrimagnetic structures
are examined on an equal footing. However, we identify that, no matter which structure is used as the
starting point, the neutron diffraction data always refines down to the ferrimagnetic structure with the Co2
atoms having antiparallel spins. In the ab initio calculations, the inclusion of spin-orbit coupling is found to be
important in the prediction of the correct magnetic ground state. Here, the results suggest that, for zero external
field and sufficiently low temperatures, the spin arrangement of YCo3 is ferrimagnetic rather than ferromagnetic
as previously believed. The fixed spin moment calculation technique has been employed to understand
the two successive field-induced magnetic transitions observed in previous magnetization measurements under
increasing ultrahigh magnetic fields. We find that the magnetic transitions start from the ferrimagnetic phase
�0.61�B/Co� and terminate with the ferromagnetic phase �1.16�B/Co�, while the spin on the Co2 atoms
progressively changes from antiparallel ferrimagnetic to paramagnetic and then to ferromagnetic. Our neutron
diffraction measurements, ab initio calculations, and the high field magnetization measurements are thus
entirely self-consistent
Microspheres Assembled from Chitosan‐Graft‐Poly(lactic acid) Micelle‐Like Core–Shell Nanospheres for Distinctly Controlled Release of Hydrophobic and Hydrophilic Biomolecules
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122426/1/mabi201600020-sup-0001-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122426/2/mabi201600020.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122426/3/mabi201600020_am.pd
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