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Temperature and load-ratio dependent fatigue-crack growth in the CrMnFeCoNi high-entropy alloy
Multiple-principal element alloys known as high-entropy alloys have rapidly been gaining attention for the vast variety of compositions and potential combinations of properties that remain to be explored. Of these alloys, one of the earliest, the âCantor alloyâ CrMnFeCoNi, displays excellent damage-tolerance with tensile strengths of âŒ1 GPa and fracture toughness values in excess of 200 MPaâm; moreover, these mechanical properties tend to further improve at cryogenic temperatures. However, few studies have explored its corresponding fatigue properties. Here we expand on our previous study to examine the mechanics and mechanisms of fatigue-crack propagation in the CrMnFeCoNi alloy (âŒ7 ÎŒm grain size), with emphasis on long-life, near-threshold fatigue behavior, specifically as a function of load ratio at temperatures between ambient and liquid-nitrogen temperatures (293 Kâ77 K). We find that ÎKth fatigue thresholds are decreased with increasing positive load ratios, R between 0.1 and 0.7, but are increased at decreasing temperature. These effects can be attributed to the role of roughness-induced crack closure, which was estimated using compliance measurements. Evidence of deformation twinning at the crack tip during fatigue-crack advance was not apparent at ambient temperatures but seen at higher stress intensities (ÎK ⌠20 MPaâm) at 77 K by post mortem microstructural analysis for tests at R = 0.1 and particularly at 0.7. Overall, the fatigue behavior of this alloy was found to be superior, or at least comparable, to conventional cryogenic and TWIP steels such as 304 L or 316 L steels and Fe-Mn steels; these results coupled with the remarkable strength and fracture toughness of the Cantor alloy at low temperatures indicate significant promise for the utility of this material for applications at cryogenic environments
New insight into cataract formation -- enhanced stability through mutual attraction
Small-angle neutron scattering experiments and molecular dynamics simulations
combined with an application of concepts from soft matter physics to complex
protein mixtures provide new insight into the stability of eye lens protein
mixtures. Exploring this colloid-protein analogy we demonstrate that weak
attractions between unlike proteins help to maintain lens transparency in an
extremely sensitive and non-monotonic manner. These results not only represent
an important step towards a better understanding of protein condensation
diseases such as cataract formation, but provide general guidelines for tuning
the stability of colloid mixtures, a topic relevant for soft matter physics and
industrial applications.Comment: 4 pages, 4 figures. Accepted for publication on Phys. Rev. Let
Parabolic groups acting on one-dimensional compact spaces
Given a class of compact spaces, we ask which groups can be maximal parabolic
subgroups of a relatively hyperbolic group whose boundary is in the class. We
investigate the class of 1-dimensional connected boundaries. We get that any
non-torsion infinite f.g. group is a maximal parabolic subgroup of some
relatively hyperbolic group with connected one-dimensional boundary without
global cut point. For boundaries homeomorphic to a Sierpinski carpet or a
2-sphere, the only maximal parabolic subgroups allowed are virtual surface
groups (hyperbolic, or virtually ).Comment: 10 pages. Added a precision on local connectedness for Lemma 2.3,
thanks to B. Bowditc
Acceleration of the Universe driven by the Casimir force
We investigate an evolutional scenario of the FRW universe with the Casimir
energy scaling like . The Casimir effect is used to explain the
vacuum energy differences (its value measured from astrophysics is so small
compared to value obtained from quantum field theory calculations). The
dynamics of the FRW model is represented in terms of a two-dimensional
dynamical system to show all evolutional paths of this model in the phase space
for all admissible initial conditions. We find also an exact solution for non
flat evolutional paths of Universe driven by the Casimir effect. The main
difference between the FRW model with the Casimir force and the CDM
model is that their generic solutions are a set of evolutional paths with a
bounce solution and an initial singularity, respectively. The evolutional
scenario are tested by using the SNIa data, FRIIb radiogalaxies, baryon
oscillation peak and CMB observation. We compare the power of explanation of
the model considered and the CDM model using the Bayesian information
criterion and Bayesian factor. Our investigation of the information criteria of
model selection showed the preference of the CDM model over the model
considered. However the presence of negative like the radiation term can remove
a tension between the theoretical and observed primordial He and D
abundance.Comment: RevTeX4, 17 pages, 9 figure
Circles in the Sky: Finding Topology with the Microwave Background Radiation
If the universe is finite and smaller than the distance to the surface of
last scatter, then the signature of the topology of the universe is writ large
on the microwave background sky. We show that the microwave background will be
identified at the intersections of the surface of last scattering as seen by
different ``copies'' of the observer. Since the surface of last scattering is a
two-sphere, these intersections will be circles, regardless of the background
geometry or topology. We therefore propose a statistic that is sensitive to all
small, locally homogeneous topologies. Here, small means that the distance to
the surface of last scatter is smaller than the ``topology scale'' of the
universe.Comment: 14 pages, 10 figures, IOP format. This paper is a direct descendant
of gr-qc/9602039. To appear in a special proceedings issue of Class. Quant.
Grav. covering the Cleveland Topology & Cosmology Worksho
An Early Universe Model with Stiff Matter and a Cosmological Constant
In the present work, we study the quantum cosmology description of a
Friedmann-Robertson-Walker model in the presence of a stiff matter perfect
fluid and a negative cosmological constant. We work in the Schutz's variational
formalism and the spatial sections have constant negative curvature. We
quantize the model and obtain the appropriate Wheeler-DeWitt equation. In this
model the states are bounded therefore we compute the discrete energy spectrum
and the corresponding eigenfunctions. In the present work, we consider only the
negative eigenvalues and their corresponding eigenfunctions. This choice
implies that the energy density of the perfect fluid is negative. A stiff
matter perfect fluid with this property produces a model with a bouncing
solution, at the classical level, free from an initial singularity. After that,
we use the eigenfunctions in order to construct wave packets and evaluate the
time-dependent expectation value of the scale factor. We find that it
oscillates between maximum and minimum values. Since the expectation value of
the scale factor never vanishes, we confirm that this model is free from an
initial singularity, also, at the quantum level.Comment: 12 Pages, 4 Figures. Final version. Accepted for publication in the
Proceedings of the 8th Friedmann Seminar, Rio de Janeiro, 2011. We restricted
our attention to treat the case where the stiff matter has negative energy
eigenvalues, following the referee's suggestio
The geometry of the light-cone cell decomposition of moduli space
S.R. is supported by STFC consolidated Grant No. ST/L000415/1 âString Theory, Gauge Theory and Dualit
Novel pyrrolobenzodiazepine benzofused hybrid molecules inhibit NF-ÎșB activity and synergise with bortezomib and ibrutinib in hematological cancers
Chronic lymphocytic leukemia (CLL) and multiple myeloma (MM) are incurable hematological malignancies that are pathologically linked with aberrant NF-ÎșB activation. In this study, we identified a group of novel C8-linked benzofused Pyrrolo[2,1-c][1,4]benzodiazepines (PBD) monomeric hybrids capable of sequence-selective inhibition of NF-ÎșB with low nanomolar LD50 values in CLL (n=46) and MM cell lines (n=5). The lead compound, DC-1-192, significantly inhibited NF-ÎșB DNA binding after just 4h exposure and demonstrating inhibitory effects on both canonical and non-canonical NF-ÎșB subunits. In primary CLL cells, sensitivity to DC-1-192 was inversely correlated with RelA subunit expression (r2=0.2) and samples with BIRC3 or NOTCH1 mutations showed increased sensitivity (P=0.001). RNA-sequencing and gene set enrichment analysis confirmed the over-representation of NF-ÎșB regulated genes in the down-regulated gene list. Furthermore, In vivo efficacy studies in NOD/SCID mice, using a systemic RPMI 8226 human multiple myeloma xenograft model, showed that DC-1-192 significantly prolonged survival (P=0.017). In addition, DC1-192 showed synergy with bortezomib and ibrutinib; synergy with ibrutinib was enhanced when CLL cells were co-cultured on CD40L-expressing fibroblasts in order to mimic the cytoprotective lymph node microenvironment (P = 0.01). Given that NF-ÎșB plays a role in both bortezomib and ibrutinib resistance mechanisms, these data provide a strong rationale for the use of DC-1-192 in the treatment of NF-ÎșB-driven cancers, particularly in the context of relapsed/refractory disease
AF-algebras and topology of mapping tori
A covariant functor from the category of mapping tori to a category of
AF-algebras is constructed; the functor takes continuous maps between such
manifolds to stable homomorphisms between the corresponding AF-algebras. We use
this functor to develop an obstruction theory for the torus bundles of
dimension 2, 3 and 4.Comment: to appear Czechoslovak Math.
Light scattering and phase behavior of Lysozyme-PEG mixtures
Measurements of liquid-liquid phase transition temperatures (cloud points) of
mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG)
show that the addition of low molecular weight PEG stabilizes the mixture
whereas high molecular weight PEG was destabilizing. We demonstrate that this
behavior is inconsistent with an entropic depletion interaction between
lysozyme and PEG and suggest that an energetic attraction between lysozyme and
PEG is responsible. In order to independently characterize the lysozyme/PEG
interactions, light scattering experiments on the same mixtures were performed
to measure second and third virial coefficients. These measurements indicate
that PEG induces repulsion between lysozyme molecules, contrary to the
depletion prediction. Furthermore, it is shown that third virial terms must be
included in the mixture's free energy in order to qualitatively capture our
cloud point and light scattering data. The light scattering results were
consistent with the cloud point measurements and indicate that attractions do
exist between lysozyme and PEG.Comment: 5 pages, 2 figures, 1 tabl
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