7,072 research outputs found
3D printing of cement composites
The aims of this study were to investigate the feasibility of generating 3D structures directly in rapid-hardening Portland cement (RHPC) using 3D Printing (3DP) technology. 3DP is a Additive Layer Manufacturing (ALM) process that generates parts directly from CAD in a layer-wise manner. 3D structures were successfully printed using a polyvinylalcohol: RHPC ratio of 3:97 w/w, with print resolutions of better than 1mm. The test components demonstrated the manufacture of features, including off-axis holes, overhangs / undercuts etc that would not be manufacturable using simple mould tools. Samples hardened by 1 day post-build immersion in water at RT offered Modulus of Rupture (MOR) values of up to 0.8±0.1MPa, and, after 26 days immersion in water at RT, offered MOR values of 2.2±0.2MPa, similar to bassanite-based materials more typically used in 3DP (1-3 MPa). Post-curing by water immersion restructured the structure, removing the layering typical of ALM processes, and infilling porosity
Branes and Black holes in Collision
We study the collision of a brane with a black hole. Our aim is to explore
the topology changing process of perforation of a brane. The brane is described
as a field theoretical domain wall in the context of an axion-like model
consisting of a complex scalar effective field theory with approximate U(1)
symmetry. We simulate numerically the dynamics of the collision and illustrate
the transition from the configuration without a hole to the pierced one with
the aid of a phase diagram. The process of perforation is found to depend on
the collisional velocity, and, contrary to our expectation, we observe that
above a critical value of the velocity, the black hole has no chance to
perforate the wall. That is: high energy collisions do not assist piercing. We
also show that, only when the model parameters are fine-tuned so that the
energy scale of the string is very close to that of the domain wall, the
collision of the wall with the black hole has a possibility to provide a
mechanism to erase domain walls, if the hole expands. However, in such cases,
domain walls will form with many holes edged by a string and therefore
disappear eventually. Therefore this mechanism is unlikely to be a solution to
the cosmological domain wall problem, although it may cause some minor effects
on the evolution of a domain wall network.Comment: 14 pages; 9 figure
Evolution of Privacy Loss in Wikipedia
The cumulative effect of collective online participation has an important and
adverse impact on individual privacy. As an online system evolves over time,
new digital traces of individual behavior may uncover previously hidden
statistical links between an individual's past actions and her private traits.
To quantify this effect, we analyze the evolution of individual privacy loss by
studying the edit history of Wikipedia over 13 years, including more than
117,523 different users performing 188,805,088 edits. We trace each Wikipedia's
contributor using apparently harmless features, such as the number of edits
performed on predefined broad categories in a given time period (e.g.
Mathematics, Culture or Nature). We show that even at this unspecific level of
behavior description, it is possible to use off-the-shelf machine learning
algorithms to uncover usually undisclosed personal traits, such as gender,
religion or education. We provide empirical evidence that the prediction
accuracy for almost all private traits consistently improves over time.
Surprisingly, the prediction performance for users who stopped editing after a
given time still improves. The activities performed by new users seem to have
contributed more to this effect than additional activities from existing (but
still active) users. Insights from this work should help users, system
designers, and policy makers understand and make long-term design choices in
online content creation systems
A Note on the Generalization of the GEMS Approach
This paper is a supplement of our earlier work JHEP 0410 (2004)
011[gr-qc/0409107].We map the vector potential of charged black holes into GEMS
and find that its effect on the thermal spectrum is the same as that on the
black hole side, i.e., it will induce a chemical potential in the thermal
spectrum which is the same as that in the charged black holes.We also argue
that the generalization of GEMS approach to non-stationary motions is not
possible.Comment: Latex file, 10 pages, no figure; v2: minor corrections; v3: revised
with title changed, one new section added and references adde
General Very Special Relativity is Finsler Geometry
We ask whether Cohen and Glashow's Very Special Relativity model for Lorentz
violation might be modified, perhaps by quantum corrections, possibly producing
a curved spacetime with a cosmological constant. We show that its symmetry
group ISIM(2) does admit a 2-parameter family of continuous deformations, but
none of these give rise to non-commutative translations analogous to those of
the de Sitter deformation of the Poincar\'e group: spacetime remains flat. Only
a 1-parameter family DISIM_b(2) of deformations of SIM(2) is physically
acceptable. Since this could arise through quantum corrections, its
implications for tests of Lorentz violations via the Cohen-Glashow proposal
should be taken into account. The Lorentz-violating point particle action
invariant under DISIM_b(2) is of Finsler type, for which the line element is
homogeneous of degree 1 in displacements, but anisotropic. We derive
DISIM_b(2)-invariant wave equations for particles of spins 0, 1/2 and 1. The
experimental bound, , raises the question ``Why is the
dimensionless constant so small in Very Special Relativity?''Comment: 4 pages, minor corrections, references adde
Non-asymptotically flat, non-AdS dilaton black holes
We show that previously known non-asymptotically flat static black hole
solutions of Einstein-Maxwell-dilaton theory may be obtained as near-horizon
limits of asymptotically flat black holes. Specializing to the case of the
dilaton coupling constant , we generate from the
non-asymptotically flat magnetostatic or electrostatic black holes two classes
of rotating dyonic black hole solutions. The rotating dyonic black holes of the
``magnetic'' class are dimensional reductions of the five-dimensional
Myers-Perry black holes relative to one of the azimuthal angles, while those of
the ``electric'' class are twisted dimensional reductions of rotating dyonic
Rasheed black strings. We compute the quasi-local mass and angular momentum of
our rotating dyonic black holes, and show that they satisfy the first law of
black hole thermodynamics, as well as a generalized Smarr formula. We also
discuss the construction of non-asymptotically flat multi-extreme black hole
configurations.Comment: Minor corrections. 2 references added. To appear in Physical Review
Statistical mechanics of Kerr-Newman dilaton black holes and the bootstrap condition
The Bekenstein-Hawking ``entropy'' of a Kerr-Newman dilaton black hole is
computed in a perturbative expansion in the charge-to-mass ratio. The most
probable configuration for a gas of such black holes is analyzed in the
microcanonical formalism and it is argued that it does not satisfy the
equipartition principle but a bootstrap condition. It is also suggested that
the present results are further support for an interpretation of black holes as
excitations of extended objects.Comment: RevTeX, 5 pages, 2 PS figures included (requires epsf), submitted to
Phys. Rev. Let
Phenotypic heterogeneity of peripheral monocytes in healthy dogs
Monocytes are key cells of the innate immune system. Their phenotypic and functional roles have been investigated in humans, mice and other animals, such as the rat, pig and cow. To date, detailed phenotypic analysis of monocytes has not been undertaken in dogs. Two important surface markers in human monocytes are CD14 and MHC class II (MHC II). By flow cytometry, we demonstrated that canine monocytes can be subdivided into three separate populations: CD14posMHC IIneg, CD14posMHC IIpos and CD14negMHC IIpos. Both light and transmission electron microscopy confirmed the monocytic identity of all three populations. The CD14posMHC IIneg population could be distinguished on an ultrastructural level by their smaller size, the presence of more numerous, larger granules, and more pseudopodia than both of the other populations
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