3,591 research outputs found
Fe adatoms along Bi lines on H/Si(001): Patterning atomic magnetic chains
The stability, electronic and magnetic properties of Fe atoms adsorbed on the
self-assembled Bi-dimer lines nanostructure on the H/Si(001) surface are
addressed by spin-density functional calculations. Our results show that Fe
adatoms are much more stable on sites closer to the Bi nanolines being able to
form one-dimensional atomic arrays. The most stable structure occurs on a
missing dimer line aside the Bi dimers, which corresponds to an array with
distances between Fe adatoms of about 8 Ang. In this array the irons are
coupled antiferromagnetically with spin magnetic moment of about 1.5 Bohr
magnetons per Fe atom, whereas the coupling exchange interactions is found to
be of 14.4 meV. We also estimate a large magnetic anisotropy energy for the Fe
adatom of about 3 meV/atom. In addition, the electronic band structure of the
Fe array at the most stable structure shows a magnetic half-metal behavior.Comment: 5 pages, 5 figures, accepted in AP
BIOERODIBLE CALCIUM SULFATE BONE GRAFTING SUBSTITUTES WITH TAILORED DRUG DELIVERY CAPABILITIES
Bone regeneration or augmentation is often required prior to or concomitant with implant placement. With the limitations of many existing technologies, a biologically compatible synthetic bone grafting substitute that is osteogenic, bioerodible, and provides spacing-making functionality while acting as a drug delivery vehicle for bioactive molecules could provide an alternative to âgold standardâ techniques.
In the first part of this work, calcium sulfate (CS) space-making synthetic bone grafts with uniformly embedded poly(ÎČ-amino ester) (PBAE) biodegradable hydrogel particles was developed to allow controlled release of bioactive agents. The embedded gel particlesâ influence on the physical and chemical characteristics of CS was tested. Namely, the compressive strength and modulus, dissolution, and morphology, were studied. All CS samples dissolved via zero-order surface erosion consistent to one another. Compression testing concluded that the amount, but not size, of embedded gel particles significantly decreased (up to 75%) the overall mechanical strength of the composite. Release studies were conducted to explore this systemâs ability to deliver a broad range of drug types and sizes. Lysozyme (model protein for larger growth factors like bone morphogenic protein [BMP]) was loaded into PBAE particles embedded in CS matrix. The release of simvastatin, a small molecule drug capable of up regulating BMP production, was also examined. The release of both lysozyme and simvastatin was governed by dissolution of CS.
The second part of this work proposed a bilayered CS implant. The physical and chemical properties were characterized similarly to the CS composites above. Release kinetics of directly loaded simvastatin in either the shell, core, or both were investigated. A sequential release of simvastatin was witnessed giving foresight of the compositeâs tunability. The sequential release of an antibacterial, metronidazole, loaded into poly(lactic-co-glycolic acid) (PLGA) particles embedded into the shell along with directly loaded simvastatin either in the shell, core, or both layers was also observed. Through controlled release of bioactive agents, as well as a tunable layered geometry, CS-based implants have the potential to be optimized in order to help streamline the steps required for the healing and regeneration of compromised bone tissue
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
The partition algebra and the Kronecker product (Extended Abstract)
We propose a new approach to study the Kronecker coefïŹcients by using the SchurâWeyl duality between
the symmetric group and the partition algebra
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