2,499 research outputs found
Visualizing polymeric components that define distinct root barriers across plant lineages
Hydrophobic cell wall depositions in roots play a key role in plant development and interaction with the soil environment, as they generate barriers that regulate bidirectional nutrient flux. Techniques to label the respective polymers are emerging, but are efficient only in thin roots or sections. Moreover, simultaneous imaging of the barrier constituents lignin and suberin remains problematic owing to their similar chemical compositions. Here, we describe a staining method compatible with single- and multiphoton confocal microscopy that allows for concurrent visualization of primary cell walls and distinct secondary depositions in one workflow. This protocol permits efficient separation of suberin- and lignin-specific signals with high resolution, enabling precise dissection of barrier constituents. Our approach is compatible with imaging of fluorescent proteins, and can thus complement genetic markers or aid the dissection of barriers in biotic root interactions. We further demonstrate applicability in deep root tissues of plant models and crops across phylogenetic lineages. Our optimized toolset will significantly advance our understanding of root barrier dynamics and function, and of their role in plant interactions with the rhizospheric environment
A cyclopentadienyl functionalized silylene-a flexible ligand for Si- And C-coordination
The synthesis of a 1,2,3,4-tetramethylcyclopentadienyl (Cp) substituted four-membered N-heterocyclic silylene [{PhC(NtBu) }Si(CMeH)] is reported first. Then, selected reactions with transition metal and a calcium precursor are shown. The proton of the Cp-unit is labile. This results in two different reaction pathways: (1) deprotonation and (2) rearrangement reactions. Deprotonation was achieved by the reaction of [{PhC(NtBu) }Si(CMeH)] with suitable zinc precursors. Rearrangement to [{PhC(NtBu) }(CMe)SiH], featuring a formally tetravalent silicon RCSi(R′)-H unit, was observed when the proton of the Cp ring was shifted from the Cp-ring to the silylene in the presence of a Lewis acid. This allows for the coordination of the Cp-ring to a calcium compound. Furthermore, upon reaction with transition metal dimers [MCl(cod)] (M = Rh, Ir; cod = 1,5-cyclooctadiene) the proton stays at the Cp-ring and the silylene reacts as a sigma donor, which breaks the dimeric structure of the precursors
A retrospective cross-sectional study: Fresh cycle endometrial thickness is a sensitive predictor of inadequate endometrial thickness in frozen embryo transfer cycles
BACKGROUND: The purpose of this study is to assess predictors of inadequate endometrial cavity thickness (ECT), defined as < 8 mm, in frozen embryo transfer (FET) cycles. METHODS: This is a retrospective cross-sectional study at an academic fertility center including 274 women who underwent their first endometrial preparation with estradiol for autologous FET in our center from 2001-2009. Multivariable logistic regression was performed to determine predictors of inadequate endometrial development in FET cycles. RESULTS: Neither age nor duration of estrogen supplementation were associated with FET endometrial thickness. Lower body mass index, nulliparity, previous operative hysteroscopy and thinner fresh cycle endometrial lining were associated with inadequate endometrial thickness in FET cycles. A maximum thickness of 11.5 mm in a fresh cycle was 80% sensitive and 70% specific for inadequate frozen cycle thickness. CONCLUSIONS: Previous fresh cycle endometrial cavity thickness is associated with subsequent FET cycle endometrial cavity thickness. Women with a fresh cycle thickness of 11.5 mm or less may require additional intervention to achieve adequate endometrial thickness in preparation for a frozen cycle
Chiral helix in AdS/CFT with flavor
The D3/D7 holographic model aims at a better approximation to QCD by adding
to N=4 SYM theory N_f of N=2 supersymmetric hypermultiplets in the fundamental
representation of SU(N_c) -- the "flavor fields" representing the quarks.
Motivated by a recent observation of the importance of the Wess-Zumino-like
(WZ) term for realizing the chiral magnetic effect within this model, we
revisit the phase diagram of the finite temperature, massless D3/D7 model in
the presence of external electric/magnetic fields and at finite chemical
potential. We point out that the A-V-V triangle anomaly represented by the WZ
term in the D7 brane probe action implies the existence of new phases that have
been overlooked in the previous studies. In the case of an external magnetic
field and at finite chemical potential, we find a "chiral helix" phase in which
the U(1)_A angle of D7 brane embedding increases monotonically along the
direction of the magnetic field -- this is a geometric realization of the
chiral spiral phase in QCD. We also show that in the case of parallel electric
and magnetic fields (E,B) there exists a phase in which the D7 brane
spontaneously begins to rotate, so that the U(1)_A angle changes as a function
of time -- this may be called the "spontaneous rotation" phase; it is a
geometrical realization of a phase with non-zero chiral chemical potential. Our
results call for a more thorough study of the (T,B,E,\mu) phase diagram of the
massless D3/D7 model taking a complete account of the WZ term.
We also speculate about the possible phase diagram in the massive case.Comment: 25 pages, 7 figure
Fracton pairing mechanism for "strange" superconductors: Self-assembling organic polymers and copper-oxide compounds
Self-assembling organic polymers and copper-oxide compounds are two classes
of "strange" superconductors, whose challenging behavior does not comply with
the traditional picture of Bardeen, Cooper, and Schrieffer (BCS)
superconductivity in regular crystals. In this paper, we propose a theoretical
model that accounts for the strange superconducting properties of either class
of the materials. These properties are considered as interconnected
manifestations of the same phenomenon: We argue that superconductivity occurs
in the both cases because the charge carriers (i.e., electrons or holes)
exchange {\it fracton excitations}, quantum oscillations of fractal lattices
that mimic the complex microscopic organization of the strange superconductors.
For the copper oxides, the superconducting transition temperature as
predicted by the fracton mechanism is of the order of K. We suggest
that the marginal ingredient of the high-temperature superconducting phase is
provided by fracton coupled holes that condensate in the conducting
copper-oxygen planes owing to the intrinsic field-effect-transistor
configuration of the cuprate compounds. For the gate-induced superconducting
phase in the electron-doped polymers, we simultaneously find a rather modest
transition temperature of K owing to the limitations imposed by
the electron tunneling processes on a fractal geometry. We speculate that
hole-type superconductivity observes larger onset temperatures when compared to
its electron-type counterpart. This promises an intriguing possibility of the
high-temperature superconducting states in hole-doped complex materials. A
specific prediction of the present study is universality of ac conduction for
.Comment: 12 pages (including separate abstract page), no figure
Controllable pi junction in a Josephson quantum-dot device with molecular spin
We consider a model for a single molecule with a large frozen spin sandwiched
in between two BCS superconductors at equilibrium, and show that this system
has a junction behavior at low temperature. The shift can be
reversed by varying the other parameters of the system, e.g., temperature or
the position of the quantum dot level, implying a controllable junction
with novel application as a Josephson current switch. We show that the
mechanism leading to the shift can be explained simply in terms of the
contributions of the Andreev bound states and of the continuum of states above
the superconducting gap. The free energy for certain configuration of
parameters shows a bistable nature, which is a necessary pre-condition for
achievement of a qubit
Large N QCD in two dimensions with a baryonic chemical potential
We consider large N gauge theory on a two dimensional lattice in the presence
of a baryonic chemical potential. We work with one copy of naive fermion and
argue that reduction holds even in the presence of a chemical potential.
Analytical arguments supported by numerical studies show that there is no phase
transition as a function of the baryonic chemical potential.Comment: 12 pages, 4 figures; Published version, typos correcte
Reflectionless tunneling in ballistic normal-metal--superconductor junctions
We investigate the phenomenon of reflectionless tunneling in ballistic
normal-metal--superconductor (NS) structures, using a semiclassical formalism.
It is shown that applied magnetic field and superconducting phase difference
both impair the constructive interference leading to this effect, but in a
qualitatively different way. This is manifested both in the conductance and in
the shot noise properties of the system considered. Unlike diffusive systems,
the features of the conductance are sharp, and enable fine spatial control of
the current, as well as single channel manipulations. We discuss the
possibility of conducting experiments in ballistic semiconductor-superconductor
structures with smooth interfaces and some of the phenomena, specific to such
structures, that could be measured. A general criterion for the barrier at NS
interfaces, though large, to be effectively transparent to pair current is
obtained.Comment: published versio
Discourses and practices in teaching methods and assessment: Insights from an early career academic
© The Author(s) 2015. Translating the purposes of education into practice is particularly challenging for those who are new or have recently entered academia. By reflecting on my first years of teaching in higher education, I discuss two key aspects of my teaching practice: shifts in choice of teaching methods and a critique of different forms of assessment. Through the discussion, I argue that a teacher needs to be reflective on both these aspects and that such reflection needs to be carried out so that the student develops into a “self-directing,” “self-monitoring,” and “self-correcting” individual. At the end of the discussion, the relevance of a “project-based learning” approach starts to become significant in taking my pedagogical practice forward
Large-N spacetime reduction and the sign and silver-blaze problems of dense QCD
We study the spacetime-reduced (Eguchi-Kawai) version of large-N QCD with
nonzero chemical potential. We explore a method to suppress the sign
fluctuations of the Dirac determinant in the hadronic phase; the method employs
a re-summation of gauge configurations that are related to each other by center
transformations. We numerically test this method in two dimensions, and find
that it successfully solves the silver-blaze problem. We analyze the system
further, and measure its free energy F, the average phase theta of its Dirac
determinant, and its chiral condensate . We show that F and
are independent of mu in the hadronic phase but that, as chiral
perturbation theory predicts, the quenched chiral condensate drops from its
mu=0 value when mu~(pion mass)/2. Finally, we find that the distribution of
theta qualitatively agrees with further, more recent, predictions from chiral
perturbation theory.Comment: 43 pages, 17 figure
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