3,238 research outputs found
Short Communication: Variability of amygdalin content in seeds of sweet and bitter apricot cultivars in Turkey
In this study, amygdalin contents in the seeds of ten different bitter or sweet apricot cultivars were determined by high performance liquid chromatography (HPLC) for two years. The seeds of apricot cultivars were obtained from the Malatya Fruit Research Institute in Turkey. The results indicated that genetic variation was found among the cultivars. The amygdalin contents of bitter cultivars were found to be higher than those of sweet cultivars. As the average of two years, the amygdalin contents of the cultivars were determined as 6.354 g/100 g in Paviot (bitter), 5.914 g/100 g in Karacabey (bitter), 4.411 g/100 g in Alyanak (bitter), 1.584 g/100 g in Cologlu (sweet), 0.970 g/100 g in Cataloglu (sweet), 0.820 g/100 g in Aprikoz (sweet), 0.729 g/100 g in Sekerpare (sweet), 0.709 g/100 g in Kabaasi (sweet), 0.610 g/100 g in Ismailaga (sweet) and 0.604 g/100 g in Hacihaliloglu (sweet).Key words: Apricot (Prunus armeniaca L.), seed, amygdalin content
Effective affirmative action in school choice
The prevalent affirmative action policy in school choice limits the number of admitted majority students to give minority students higher chances to attend their desired schools. There have been numerous efforts to reconcile affirmative action policies with celebrated matching mechanisms such as the deferred acceptance and top trading cycles algorithms. Nevertheless, it is theoretically shown that under these algorithms, the policy based on majority quotas may be detrimental to minorities. Using simulations, we find that this is a more common phenomenon rather than a peculiarity. To circumvent the inefficiency caused by majority quotas, we offer a different interpretation of the affirmative action policies based on minority reserves. With minority reserves, schools give higher priority to minority students up to the point that the minorities fill the reserves. We compare the welfare effects of these policies. The deferred acceptance algorithm with minority reserves Pareto dominates the one with majority quotas. Our simulations, which allow for correlations between student preferences and school priorities, indicate that minorities are, on average, better off with minority reserves while adverse effects on majorities are mitigated. © 2013 Isa E. Hafalir, M. Bumin Yenmez, and Muhammed A. Yildirim
Exo-hydrogenated Single Wall Carbon Nanotubes
An extensive first-principles study of fully exo-hydrogenated zigzag (n,0)
and armchair (n,n) single wall carbon nanotubes (CH), polyhedral
molecules including cubane, dodecahedrane, and CH points to
crucial differences in the electronic and atomic structures relevant to
hydrogen storage and device applications. CH's are estimated to be
stable up to the radius of a (8,8) nanotube, with binding energies proportional
to 1/R. Attaching a single hydrogen to any nanotube is always exothermic.
Hydrogenation of zigzag nanotubes is found to be more likely than armchair
nanotubes with similar radius. Our findings may have important implications for
selective functionalization and finding a way of separating similar radius
nanotubes from each other.Comment: 5 pages, 4 postscript figures, Revtex file, To be appear in Physical
Review
Magnetic Excitations of Undoped Iron Oxypnictides
We study the magnetic excitations of undoped iron oxypnictides using a
three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms
of the spin wave dispersion, velocities, and structure factor are given. Aside
from quantitative comparisons which can be made to inelastic neutron scattering
experiments, we also give qualitative criteria which can distinguish various
regimes of coupling strength. The magnetization reduction due to quantum zero
point fluctuations shows clear dependence on the c-axis coupling.Comment: 4 pages, 5 figures, to appear in Frontiers of Physics in China: a
special issue on Iron-based superconductor
On the multi-orbital band structure and itinerant magnetism of iron-based superconductors
This paper explains the multi-orbital band structures and itinerant magnetism
of the iron-pnictide and chalcogenides. We first describe the generic band
structure of an isolated FeAs layer. Use of its Abelian glide-mirror group
allows us to reduce the primitive cell to one FeAs unit. From
density-functional theory, we generate the set of eight Fe and As
localized Wannier functions for LaOFeAs and their tight-binding (TB)
Hamiltonian, . We discuss the topology of the bands, i.e. allowed and
avoided crossings, the origin of the d6 pseudogap, as well as the role of the
As orbitals and the elongation of the FeAs tetrahedron. We then
couple the layers, mainly via interlayer hopping between As orbitals,
and give the formalism for simple and body-centered tetragonal stackings. This
allows us to explain the material-specific 3D band structures. Due to the high
symmetry, several level inversions take place as functions of or
pressure, resulting in linear band dispersions (Dirac cones). The underlying
symmetry elements are, however, easily broken, so that the Dirac points are not
protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian,
we form the band structures for spin spirals with wavevector by coupling
and . The band structure for stripe order is studied as a
function of the exchange potential, , using Stoner theory. Gapping of
the Fermi surface (FS) for small requires matching of FS dimensions
(nesting) and -orbital characters. The origin of the propeller-shaped FS is
explained. Finally, we express the magnetic energy as the sum over
band-structure energies, which enables us to understand to what extent the
magnetic energies might be described by a Heisenberg Hamiltonian, and the
interplay between the magnetic moment and the elongation of the FeAs4
tetrahedron
Importance of Itinerancy and Quantum Fluctuations for the Magnetism in Iron Pnictides
By applying density functional theory, we find strong evidence for an
itinerant nature of magnetism in two families of iron pnictides. Furthermore,
by employing dynamical mean field theory with continuous time quantum Monte
Carlo as an impurity solver, we observe that the antiferromagnetic metal with
small magnetic moment naturally arises out of coupling between unfrustrated and
frustrated bands. Our results point to a possible scenario for magnetism in
iron pnictides where magnetism originates from a strong instability at the
momentum vector (, , ) while it is reduced by quantum
fluctuations due to the coupling between weakly and strongly frustrated bands.Comment: 4 pages, 4 figure
Optimal drug combinations and minimal hitting sets
<p>Abstract</p> <p>Background</p> <p>Identifying effective drug combinations that significantly improve over single agents is a challenging problem. Pairwise combinations already represent a huge screening effort. Beyond two drug combinations the task seems unfeasible.</p> <p>Results</p> <p>In this work we introduce a method to uncover drug combinations with a putative effective response when presented to a heterogeneous population of malignant agents (strains), such as cancer cell lines or viruses. Using data quantifying the effect of single drugs over several individual strains, we search for minimal drug combinations that successfully target all strains. We show that the latter problem can be mapped to a minimal hitting set problem in mathematics. We illustrate this approach using data for the NCI60 panel of tumor derived cell lines, uncovering 14 anticancer drug combinations.</p> <p>Conclusion</p> <p>The drug-response graph and the associated minimal hitting set method can be used to uncover effective drug combinations in anticancer drug screens and drug development programs targeting heterogeneous populations of infectious agents such as HIV.</p
Improved Network Performance via Antagonism: From Synthetic Rescues to Multi-drug Combinations
Recent research shows that a faulty or sub-optimally operating metabolic
network can often be rescued by the targeted removal of enzyme-coding
genes--the exact opposite of what traditional gene therapy would suggest.
Predictions go as far as to assert that certain gene knockouts can restore the
growth of otherwise nonviable gene-deficient cells. Many questions follow from
this discovery: What are the underlying mechanisms? How generalizable is this
effect? What are the potential applications? Here, I will approach these
questions from the perspective of compensatory perturbations on networks.
Relations will be drawn between such synthetic rescues and naturally occurring
cascades of reaction inactivation, as well as their analogues in physical and
other biological networks. I will specially discuss how rescue interactions can
lead to the rational design of antagonistic drug combinations that select
against resistance and how they can illuminate medical research on cancer,
antibiotics, and metabolic diseases.Comment: Online Open "Problems and Paradigms" articl
Electronic Structure of Fe-Based Superconductors
The electronic structure of the Fe-based superconductors is discussed, mainly
from the point of view of first principles calculations in relation to
experimental data. Comparisons and contrasts with cuprates are made. The
problem of reconciling experiments indicating an symmetry gap with
experiments indicating line nodes is discussed and a possible resolution is
given.Comment: Updated references. Additional discussio
Structural and superconducting properties in LaFeAs1-xSbxO1-yFy
We report the antimony (Sb) doping effect in a prototype system of iron-based
supercon-ductors LaFeAsO1-yFy (y=0, 0.1, 0.15). X-ray powder diffraction
indicates that the lattice pa-rameters increase with Sb content within the
doping limit. Rietveld structural refinements show that, with the partial
substitution of Sb for As, while the thickness of the Fe2As2 layers increases
significantly, that of the La2O2 layers shrinks simultaneously. So a negative
chemical pressure is indeed "applied" to the superconducting-active Fe2As2
layers, in con-trast to the effect of positive chemical pressure by the
phosphorus doping. Electrical resis-tance and magnetic susceptibility
measurements indicate that, while the Sb doping hardly influences the SDW
anomaly in LaFeAsO, it recovers SDW order for the optimally-doped sample of
y=0.1. In the meantime, the superconducting transition temperature can be
raised up to 30 K in LaFeAs1-xSbxO1-yFy with x=0.1 and y=0.15. The Sb doping
effects are discussed in term of both J1-J2 model and Fermi Surface (FS)
nesting scenario.Comment: 7 pages, 4 figures, 1 table. to be published in Science in China
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