1,388 research outputs found
Relaxed Three-Algebras: Their Matrix Representations and Implications for Multi M2-brane Theory
We argue that one can relax the requirements of the non-associative
three-algebras recently used in constructing D=3, N=8 superconformal field
theories, and introduce the notion of ``relaxed three-algebras''. We present a
specific realization of the relaxed three-algebras in terms of classical Lie
algebras with a matrix representation, endowed with a non-associative
four-bracket structure which is prescribed to replace the three-brackets of the
three-algebras. We show that both the so(4)-based solutions as well as the
cases with non-positive definite metric find a uniform description in our
setting. We discuss the implications of our four-bracket representation for the
D=3, N=8 and multi M2-brane theory and show that our setup can shed light on
the problem of negative kinetic energy degrees of freedom of the Lorentzian
case.Comment: 31 pages, no figure
On phase behavior and dynamical signatures of charged colloidal platelets
We investigate the competition between anisotropic excluded-volume and
repulsive electrostatic interactions in suspensions of thin charged colloidal
discs, by means of Monte-Carlo simulations and dynamical characterization of
the structures found. We show that the original intrinsic anisotropy of the
electrostatic potential between charged platelets, obtained within the
non-linear Poisson-Boltzmann formalism, not only rationalizes the generic
features of the complex phase diagram of charged colloidal platelets such as
Gibbsite and Beidellite clays, but also predicts the existence of novel
structures. In addition, we find evidences of a strong slowing down of the
dynamics upon increasing density.Comment: 6 pages, 6 Figure
Bacterial fitness shapes the population dynamics of antibiotic-resistant and -susceptible bacteria in a model of combined antibiotic and anti-virulence treatment
Bacterial resistance to antibiotic treatment is a huge concern: introduction
of any new antibiotic is shortly followed by the emergence of resistant
bacterial isolates in the clinic. This issue is compounded by a severe lack of
new antibiotics reaching the market. The significant rise in clinical
resistance to antibiotics is especially problematic in nosocomial infections,
where already vulnerable patients may fail to respond to treatment, causing
even greater health concern. A recent focus has been on the development of
anti-virulence drugs as a second line of defence in the treatment of
antibiotic-resistant infections. This treatment, which weakens bacteria by
reducing their virulence rather than killing them, should allow infections to
be cleared through the body's natural defence mechanisms. In this way there
should be little to no selective pressure exerted on the organism and, as such,
a predominantly resistant population would be unlikely to emerge. However, much
controversy surrounds this approach with many believing it would not be
powerful enough to clear existing infections, restricting its potential
application to prophylaxis. We have developed a mathematical model that
provides a theoretical framework to reveal the circumstances under which
anti-virulence drugs may or may not be successful. We demonstrate that by
harnessing and combining the advantages of antibiotics with those provided by
anti-virulence drugs, given infection-specific parameters, it is possible to
identify treatment strategies that would efficiently clear bacterial
infections, while preventing the emergence of resistant subpopulations. Our
findings strongly support the continuation of research into anti-virulence
drugs and demonstrate that their applicability may reach beyond infection
prevention.Comment: Pre-review manuscript. Submitted to Journal of Theoretical Biology,
July 21st 201
Dynamic Monte Carlo Simulations of Anisotropic Colloids
We put forward a simple procedure for extracting dynamical information from
Monte Carlo simulations, by appropriate matching of the short-time diffusion
tensor with its infinite-dilution limit counterpart, which is supposed to be
known. This approach --discarding hydrodynamics interactions-- first allows us
to improve the efficiency of previous Dynamic Monte Carlo algorithms for
spherical Brownian particles. In a second step, we address the case of
anisotropic colloids with orientational degrees of freedom. As an illustration,
we present a detailed study of the dynamics of thin platelets, with emphasis on
long-time diffusion and orientational correlations.Comment: 12 pages, 9 figure
in generalized supergravity
We showed in previous work that for homogeneous Yang-Baxter (YB) deformations
of AdSS, the open string metric and coupling, and as a result the
closed string density , remain undeformed. In this work,
in addition to extending these results to the deformation associated with the
modified CYBE, or -deformation, we identify the Page forms as the open
string counterpart for RR fields and demonstrate case by case that the non-zero
Page forms remain invariant under YB deformations. We give a physical meaning
to the Killing vector of generalized supergravity and show for all YB
deformations: 1) appears as a current for center of mass motion on the
worldvolume of a D-branes probing the background, 2) is equal to the
divergence of the noncommutativity parameter, 3) exhibits "holographic"
behavior, where the radial component of vanishes at the AdS boundary, and
4) in pure spinor formalism is related to a certain state in the BRST
cohomology.Comment: 11 pages, 2 column; v2 references updated; v3 to appear in EPJ
Comments on Multiple M2-branes
Recently a three-dimensional field theory was derived that is consistent with
all the symmetries expected of the worldvolume action for multiple M2-branes.
In this note we examine several physical predictions of this model and show
that they are in agreement with expected M2-brane dynamics. In particular, we
discuss the quantization of the Chern-Simons coefficient, the vacuum moduli
space, a massive deformation leading to fuzzy three-sphere vacua, and a
possible large n limit. In this large n limit, the fuzzy funnel solution
correctly reproduces the mass of an M5-brane.Comment: 18 pages. Published versio
Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after Longâterm Use In Vivo. Part 3: Preload and Tensile Fracture Load Testing
Purpose: The aim of this study was to determine the preload and tensile fracture load values of prosthetic retaining screws after longâterm use in vivo compared to unused screws (controls). Additionally, the investigation addressed whether the preload and fracture load values of prosthetic retaining screws reported by the manufacturer become altered after longâterm use in vivo.
Materials and Methods: For preload testing, 10 new screws (controls) from Nobel Biocare (NB) and 73 used retaining screws [58 from NB and 15 from Sterngold (SG)] were subjected to preload testing. For tensile testing, eight controls from NB and 58 used retaining screws (46 from NB and 12 from SG) were subjected to tensile testing. Used screws for both tests were in service for 18â120 months. A custom load frame, load cell, and torque wrench setup were used for preload testing. All 83 prosthetic screws were torqued once to 10 Ncm, and the produced preload value was recorded (N) using an XâY plotter. Tensile testing was performed on a universal testing machine and the resulting tensile fracture load value was recorded (N). Preload and tensile fracture load values were analyzed with 2âway ANOVA and Tukey postâhoc tests.
Results: There was a significant difference between preload values for screws from NB and screws from SG (p \u3c 0.001). The preload values for gold alloy screws from NB decreased as the number of years in service increased. There was a significant difference between tensile fracture values for the three groups (gold alloy screws from NB and SG and palladium alloy screws from NB) at p \u3c 0.001. The tensile fracture values for gold alloy screws from NB and SG decreased as the number of years in service increased.
Conclusions: In fixed detachable hybrid prostheses, perhaps as a result of galling, the intended preload values of prosthetic retaining screws may decrease with increased inâservice time. The reduction of the fracture load value may be related to the increase of inâservice time; however, the actual determination of this relationship is not possible from this study alone
Mechanical Behavior and Failure Analysis of Prosthetic Retaining Screws after LongâTerm Use In Vivo. Part 2: Metallurgical and Microhardness Analysis
Abstract
Purpose: This study involved testing and analyzing multiple retrieved prosthetic retaining screws after longâterm use in vivo to: (1) detect manufacturing defects that could affect inâservice behavior; (2) characterize the microstructure and alloy composition; and (3) further characterize the wear mechanism of the screw threads.
Materials and Methods: Two new (control) screws from Nobel Biocare (NB) and 18 used (in service 18â120 months) retaining screws [12 from NB and 6 from Sterngold (SG)] were: (1) metallographically examined by light microscopy and scanning electron microscopy (SEM) to determine the microstructure; (2) analyzed by energy dispersive Xâray (EDX) microanalysis to determine the qualitative and semiquantitative average alloy and individual phase compositions; and (3) tested for Vickers microhardness.
Results: Examination of polished longitudinal sections of the screws using light microscopy revealed a significant defect in only one Group 4 screw. No significant defects in any other screws were observed. The defect was considered a âseamâ originating as a âhot tearâ during original casting solidification of the alloy. Additionally, the examination of longitudinal sections of the screws revealed a uniform homogeneous microstructure in some groups, while in other groups the sections exhibited rows of second phase particles. The screws for some groups demonstrated severe deformation of the lower threads and the bottom part of the screw leading to the formation of crevices and grooves. Some NB screws were comprised of Auâbased alloy with Pt, Cu, and Ag as alloy elements, while others (Groups 4 and 19) were Pdâbased with Ga, Cu, and Au alloy elements. The microstructure was homogeneous with fine or equiaxed grains for all groups except Group 4, which appeared inhomogeneous with anomalous grains. SG screws demonstrated a typical dendritic structure and were Auâbased alloy with Cu and Ag alloy elements. There were differences in the microhardness of gold alloy screws from NB and SG as well as palladium alloy screws from NB.
Conclusions: Significant differences within NB retaining screws and between NB and SG screws were found for microstructure, major alloy constituents, and microhardness
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