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Fabrication of Bone Substitute Material by Rapid Prototyping
Bone tissue engineering has gained much attention in recent years. A key requirement in this
field is the development of scaffold structures, on which cells adhere. This can be done by
fabricating scaffolds by direct procedures like 3D-printing or by indirect procedures like casting.
With the 3D-printing process different structures were build up by using hydroxyapatite powder
(HA) and a special binder material. Afterwards the printed 3D structures were sintered.
For the casting process molds have been made of different resins by stereolithography and other
processes using polymers and waxes. These structures were filled by a suspension of HA. By
heating the resulting polymer/ceramic composite to a specific temperature it is possible to
combust the polymer or wax. By further heating the remaining body, the HA is sintered.
Compared to the 3D printing a better resolution can be obtained here. But there are restrictions
regarding the ratio of polymer and the HA ceramic during the heating process which means a
limitation for the level of porosity.Mechanical Engineerin
Case studies: the environmental impact of DSM projects
Abstract: The critical electricity supply situation in South Africa has brought about the implementation of DSM projects in various industries including the gold mines. However, in certain cases, this may have a negative impact on the environment. As a result of this problem a need to maximise load shifting results with minimal environmental impact has become imperative. This paper presents a study of the possible impact on the environment when attempting load shifting
Нові документи про родину Лисянських
Het lijkt een wet van Meden en Perzen: in tijden van
crisis duikt ook steeds een roep om ingrijpende
verandering op. Constante in deze dynamiek is het
concept van de rechtvaardige stad. Hoewel al in de
jaren zeventig geïntroduceerd, is het nog steeds
onderdeel van verhit debat. In deze AGORA een
historische en theoretische refl ectie en een analyse
van rechtvaardigheid in de stedelijke praktijk
Significant Conditions on the Two-electron Reduced Density Matrix from the Constructive Solution of N-representability
We recently presented a constructive solution to the N-representability
problem of the two-electron reduced density matrix (2-RDM)---a systematic
approach to constructing complete conditions to ensure that the 2-RDM
represents a realistic N-electron quantum system [D. A. Mazziotti, Phys. Rev.
Lett. 108, 263002 (2012)]. In this paper we provide additional details and
derive further N-representability conditions on the 2-RDM that follow from the
constructive solution. The resulting conditions can be classified into a
hierarchy of constraints, known as the (2,q)-positivity conditions where the q
indicates their derivation from the nonnegativity of q-body operators. In
addition to the known T1 and T2 conditions, we derive a new class of
(2,3)-positivity conditions. We also derive 3 classes of (2,4)-positivity
conditions, 6 classes of (2,5)-positivity conditions, and 24 classes of
(2,6)-positivity conditions. The constraints obtained can be divided into two
general types: (i) lifting conditions, that is conditions which arise from
lifting lower (2,q)-positivity conditions to higher (2,q+1)-positivity
conditions and (ii) pure conditions, that is conditions which cannot be derived
from a simple lifting of the lower conditions. All of the lifting conditions
and the pure (2,q)-positivity conditions for q>3 require tensor decompositions
of the coefficients in the model Hamiltonians. Subsets of the new
N-representability conditions can be employed with the previously known
conditions to achieve polynomially scaling calculations of ground-state
energies and 2-RDMs of many-electron quantum systems even in the presence of
strong electron correlation
Role of dispersion of vanadia on SBA-15 in the oxidative dehydrogenation of propane
A series of vanadia catalysts supported on the mesoporous silica SBA-15 are synthesized using an automated laboratory reactor. The catalysts contain from 0.6 up to 13.6V atoms/nm2 and are structurally characterized by various techniques (BET, XRD, SEM, TEM, Raman, IR, UV/Vis). Samples containing up to 3.1V/nm2 are structurally rather similar. They all contain a mixture of tetrahedral (VOx)n species, both monomeric and oligomeric. The ratio of monomeric and oligomeric species depends on the vanadia loading. At the highest loading of 13.6V/nm2, in addition to tetrahedral (VOx)n, also substantial amounts of three-dimensional, bulk-like V2O5 are present in the catalyst. The structural similarity of the low-loaded catalysts is reflected in their alike catalytical activity during the oxidative dehydrogenation (ODH) of propane between 380 and 480 °C. Propene, CO, and CO2 are formed as reaction products, while neither the formation of ethene nor acrolein or acrylic acid is observed in other than trace amounts. The activation energy for ODH of propane is not, vert, similar140 kJ/mol. The catalyst with the highest loading yields varying activation energies for different reaction conditions, which is probably related to rearrangements between bulk-like and dispersed, two-dimensional (VOx)n. Rather than the monomer to oligomer ratio, the ratio of two-dimensional to three-dimensional vanadia seems to be crucial for the catalytic properties of silica supported vanadia in the ODH of propane
Influence of scattering coefficient on the prediction of room acoustic parameters in a virtual concert hall.
The scattering coefficient is one of the most important input parameters in room acoustics simulations. Together with absorption coefficient they belong to main descriptors of interior surface properties in the calculation process based on ray or radiosity method algorithms.
This paper investigates the influence of scattered sound on the objective room acoustical parameters in the example of a virtual concert hall. Six different alternatives were simulated, where scattering coefficients s = 10, 30, 50, 60, 70 and 90 % respectively, were applied to the interior surfaces of the ceiling, side and rear walls. Analysis has been performed by studying the
results of objective room acoustical parameters predicted by simulations done in the software Catt-Acoustic®
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