3,455 research outputs found
Bioactive composites for bone tissue engineering
One of the major challenges of bone tissue engineering is the production of a suitable scaffold material. In this review the current composite materials options available are considered covering both the methods of both production and assessing the scaffolds. A range of production routes have been investigated ranging from the use of porogens to produce the porosity through to controlled deposition methods. The testing regimes have included mechanical testing of the materials produced through to in vivo testing of the scaffolds. While the ideal scaffold material has not yet been produced, progress is being made
Cloning and Functional Analysis of three Cold Regulated <em>CBF</em> Genes in the Overwintering Crucifer <em>Boechera stricta</em>
In this research, we isolated three CBF (C-repeat-Binding Factors) genes from two genotypes of Boechera stricta with contrasting freezing tolerance and characterized their structure and expression patterns in response to cold treatment. An amino acid sequence comparison revealed that the CBF genes in B. stricta showed high conservation in the AP2 domain and PKKP/RAGR motif like other cold adaptable Brassicaceae. The pairwise sequence alignment of the CBF genes isolated from two genotypes of B. stricta showed non-synonymous mutations in CBF 2 and 3. Gene expression analysis demonstrated that CBF genes in B. stricta have expression patterns similar to CBFs in A. thaliana in response to cold treatment, while differential expression at the molecular level in CBF and COR genes was presented between two genotypes of B. stricta. Our results suggest that signal transduction of three CBF genes can be one of the central pathways in the development of freezing tolerance in B. stricta
Magnetic interactions in transition metal doped ZnO : An abinitio study
We calculate the nature of magnetic interactions in transition-metal doped
ZnO using the local spin density approximation and LSDA+\textit{U} method of
density functional theory. We investigate the following four cases: (i) single
transition metal ion types (Cr, Mn, Fe, Co, Ni and Cu) substituted at Zn sites,
(ii) substitutional magnetic transition metal ions combined with additional Cu
and Li dopants, (iii) substitutional magnetic transition metal ions combined
with oxygen vacancies and (iv) pairs of magnetic ion types (Co and Fe, Co and
Mn, etc.). Extensive convergence tests indicate that the calculated magnetic
ground state is unusually sensitive to the k-point mesh and energy cut-off, the
details of the geometry optimizations and the choice of the
exchange-correlation functional. We find that ferromagnetic coupling is
sometimes favorable for single type substitutional transition metal ions within
the local spin density approximation. However, the nature of magnetic
interactions changes when correlations on the transition-metal ion are treated
within the more realistic LSDA + \textit{U} method, often disfavoring the
ferromagnetic state. The magnetic configuration is sensitive to the detailed
arrangement of the ions and the amount of lattice relaxation, except in the
case of oxygen vacancies when an antiferromagnetic state is always favored.Comment: 11 pages, 17 figure
Non-monotonic temperature dependent transport in graphene grown by Chemical Vapor Deposition
Temperature-dependent resistivity of graphene grown by chemical vapor
deposition (CVD) is investigated. We observe in low mobility CVD graphene
device a strong insulating behavior at low temperatures and a metallic behavior
at high temperatures manifesting a non-monotonic in the temperature dependent
resistivity.This feature is strongly affected by carrier density modulation. To
understand this anomalous temperature dependence, we introduce thermal
activation of charge carriers in electron-hole puddles induced by randomly
distributed charged impurities. Observed temperature evolution of resistivity
is then understood from the competition among thermal activation of charge
carriers, temperature-dependent screening and phonon scattering effects. Our
results imply that the transport property of transferred CVD-grown graphene is
strongly influenced by the details of the environmentComment: 7 pages, 3 figure
Z_3 Strings and their Interactions
We construct Z_3 vortex solutions in a model in which SU(3) is spontaneously
broken to Z_3. The model is truncated to one in which there are only two
dimensionless free parameters and the interaction of vortices within this
restricted set of models is studied numerically. We find that there is a curve
in the two dimensional space of parameters for which the energy of two
asymptotically separated vortices equals the energy of the vortices at
vanishing separation. This suggests that the inter-vortex potential for Z_3
strings might be flat for these couplings, much like the case of U(1) strings
in the Bogomolnyi limit. However, we argue that the intervortex potential is
attractive at short distances and repulsive at large separations leading to the
possibility of unstable bound states of Z_3 vortices.Comment: 8 pages; mainly corrected typos in table
Spontaneous Symmetry Breaking of Population between Two Dynamic Attractors in a Driven Atomic Trap: Ising-class Phase Transition
We have observed spontaneous symmetry breaking of atomic populations in the
dynamic phase-space double-potential system, which is produced in the
parametrically driven magneto-optical trap of atoms. We find that the system
exhibits similar characteristics of the Ising-class phase transition and the
critical value of the control parameter, which is the total atomic number, can
be calculated. In particular, the collective effect of the laser shadow becomes
dominant at large atomic number, which is responsible for the population
asymmetry of the dynamic two-state system. This study may be useful for
investigation of dynamic phase transition and temporal behaviour of critical
phenomena.Comment: 4 pages, 4 figure
Raman-scattered O VI Features in the Symbiotic Nova RR Telescopii
RR Tel is an interacting binary system in which a hot white dwarf (WD) accretes matter from a Mira-type variable star via gravitational capture of its stellar wind. This symbiotic nova shows intense Raman-scattered O VI 1032 and 1038 features at 6825 ËšA and 7082 ËšA. We present high-resolution optical spectra of RR Tel taken in 2016 and 2017 with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at Magellan-Clay telescope, Chile. We aim to study the stellar wind accretion in RR Tel from the profile analysis of Raman O VI features. With an asymmetric O VI disk model, we derive a representative Keplerian speed of > 35 km s−1 , and the corresponding scale < 0.8 au. The best-fit for the Raman profiles is obtained with a mass loss rate of the Mira MË™ ∼ 2 × 10−6 M yr−1 and a wind terminal velocity v∞ ∼ 20 km s−1 . We compare the MIKE data with an archival spectrum taken in 2003 with the Fibre-fed Extended Range Optical Spectrograph (FEROS) at the MPG/ESO 2.2 m telescope. It allows us to highlight the profile variation of the Raman O VI features, indicative of a change in the density distribution of the O VI disk in the last two decades. We also report the detection of O VI recombination lines at 3811 ËšA and 3834 ËšA, which are blended with other emission lines. Our profile decomposition suggests that the recombination of O VII takes place nearer to the WD than the O VI 1032 and 1038 emission region.Fil: Heo, J. E.. Observatorio Gemini; Chile. Universidad de La Serena; Chile. Sejong University; Corea del SurFil: Lee, H. W.. Universidad de Sejong; Corea del SurFil: Angeloni, R.. Universidad de La Serena; ChileFil: Palma, Tali. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de AstrofÃsica Estelar; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba; ArgentinaFil: Di Mille, F.. Observatorio Las Campanas; Chil
Long-term prognosis for individuals with hypertension undergoing coronary artery calcium scoring
To examine the performance of coronary artery calcification (CAC) for stratifying long-term risk of death in asymptomatic hypertensive patients
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