571 research outputs found
Casein Kinase 1 Promotes Initiation of Clathrin-Mediated Endocytosis
SummaryIn budding yeast, over 60 proteins functioning in at least five modules are recruited to endocytic sites with predictable order and timing. However, how sites of clathrin-mediated endocytosis are initiated and stabilized is not well understood. Here, the casein kinase 1 (CK1) Hrr25 is shown to be an endocytic protein and to be among the earliest proteins to appear at endocytic sites. Hrr25 absence or overexpression decreases or increases the rate of endocytic site initiation, respectively. Ede1, an early endocytic Eps15-like protein important for endocytic initiation, is an Hrr25 target and is required for Hrr25 recruitment to endocytic sites. Hrr25 phosphorylation of Ede1 is required for Hrr25-Ede1 interaction and promotes efficient initiation of endocytic sites. These observations indicate that Hrr25 kinase and Ede1 cooperate to initiate and stabilize endocytic sites. Analysis of the mammalian homologs CK1Ύ/Δ suggests a conserved role for these protein kinases in endocytic site initiation and stabilization
Reactions of Sodium Bis(N-aryliminophosphoranyl)alkanides with Halide-Bridged Platinum(II) and Palladium(II) Phosphine Dimers Affording Four-Membered M-N-P-C Metallacycles and Orthometalated Platinum(II) and Palladium(II) Complexes
Atomic Model of Susy Hubbard Operators
We apply the recently proposed susy Hubbard operators to an atomic model. In
the limiting case of free spins, we derive exact results for the entropy which
are compared with a mean field + gaussian corrections description. We show how
these results can be extended to the case of charge fluctuations and calculate
exact results for the partition function, free energy and heat capacity of an
atomic model for some simple examples. Wavefunctions of possible states are
listed. We compare the accuracy of large N expansions of the susy spin
operators with those obtained using `Schwinger bosons' and `Abrikosov
pseudo-fermions'. For the atomic model, we compare results of slave boson,
slave fermion, and susy Hubbard operator approximations in the physically
interesting but uncontrolled limiting case of N->2. For a mixed representation
of spins we estimate the accuracy of large N expansions of the atomic model. In
the single box limit, we find that the lowest energy saddle-point solution
reduces to simply either slave bosons or slave fermions, while for higher boxes
this is not the case. The highest energy saddle-point solution has the
interesting feature that it admits a small region of a mixed representation,
which bears a superficial resemblance to that seen experimentally close to an
antiferromagnetic quantum critical point.Comment: 17 pages + 7 pages Appendices, 14 figures. Substantial revision
Magnetic and lattice polaron in Holstein-t-J model
We investigate the interplay between the formation of lattice and magnetic
polaron in the case of a single hole in the antiferromagnetic background. We
present an exact analytical solution of the Holstein-t-J model in infinite
dimensions. Ground state energy, electron-lattice correlation function, spin
bag dimension as well as spectral properties are calculated. The magnetic and
hole-lattice correlations sustain each other, i.e. the presence of
antiferromagnetic correlations favors the formation of the lattice polaron at
lower value of the electron-phonon coupling while the polaronic effect
contributes to reduce the number of spin defects in the antiferromagnetic
background. The crossover towards a spin-lattice small polaron region of the
phase diagram becomes a discontinuous transition in the adiabatic limit.Comment: revtex, 8 eps figures included NEW version. Appendix with a full
proof include
Measuring the decoherence rate in a semiconductor charge qubit
We describe a method by which the decoherence time of a solid state qubit may
be measured. The qubit is coded in the orbital degree of freedom of a single
electron bound to a pair of donor impurities in a semiconductor host. The qubit
is manipulated by adiabatically varying an external electric field. We show
that, by measuring the total probability of a successful qubit rotation as a
function of the control field parameters, the decoherence rate may be
determined. We estimate various system parameters, including the decoherence
rates due to electromagnetic fluctuations and acoustic phonons. We find that,
for reasonable physical parameters, the experiment is possible with existing
technology. In particular, the use of adiabatic control fields implies that the
experiment can be performed with control electronics with a time resolution of
tens of nanoseconds.Comment: 9 pages, 6 figures, revtex
Single-electron transport driven by surface acoustic waves: moving quantum dots versus short barriers
We have investigated the response of the acoustoelectric current driven by a
surface-acoustic wave through a quantum point contact in the closed-channel
regime. Under proper conditions, the current develops plateaus at integer
multiples of ef when the frequency f of the surface-acoustic wave or the gate
voltage Vg of the point contact is varied. A pronounced 1.1 MHz beat period of
the current indicates that the interference of the surface-acoustic wave with
reflected waves matters. This is supported by the results obtained after a
second independent beam of surface-acoustic wave was added, traveling in
opposite direction. We have found that two sub-intervals can be distinguished
within the 1.1 MHz modulation period, where two different sets of plateaus
dominate the acoustoelectric-current versus gate-voltage characteristics. In
some cases, both types of quantized steps appeared simultaneously, though at
different current values, as if they were superposed on each other. Their
presence could result from two independent quantization mechanisms for the
acoustoelectric current. We point out that short potential barriers determining
the properties of our nominally long constrictions could lead to an additional
quantization mechanism, independent from those described in the standard model
of 'moving quantum dots'.Comment: 25 pages, 12 figures, to be published in a special issue of J. Low
Temp. Phys. in honour of Prof. F. Pobel
Low energy and dynamical properties of a single hole in the t-Jz model
We review in details a recently proposed technique to extract information
about dynamical correlation functions of many-body hamiltonians with a few
Lanczos iterations and without the limitation of finite size. We apply this
technique to understand the low energy properties and the dynamical spectral
weight of a simple model describing the motion of a single hole in a quantum
antiferromagnet: the model in two spatial dimension and for a double
chain lattice. The simplicity of the model allows us a well controlled
numerical solution, especially for the two chain case. Contrary to previous
approximations we have found that the single hole ground state in the infinite
system is continuously connected with the Nagaoka fully polarized state for
. Analogously we have obtained an accurate determination of the
dynamical spectral weight relevant for photoemission experiments. For
an argument is given that the spectral weight vanishes at the Nagaoka energy
faster than any power law, as supported also by a clear numerical evidence. It
is also shown that spin charge decoupling is an exact property for a single
hole in the Bethe lattice but does not apply to the more realistic lattices
where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to
appear in Phys. Rev
Holes in the t-J_z model: a thorough study
The t-J_z model is the strongly anisotropic limit of the t-J model which
captures some general properties of the doped antiferromagnets (AF). The
absence of spin fluctuations simplifies the analytical treatment of hole motion
in an AF background and allows us to calculate the single- and two-hole spectra
with high accuracy using regular diagram technique combined with real-space
approach. At the same time, numerical studies of this model via exact
diagonalization (ED) on small clusters show negligible finite size effects for
a number of quantities, thus allowing a direct comparison between analytical
and numerical results. Both approaches demonstrate that the holes have tendency
to pair in the p- and d-wave channels at realistic values of t/J. The
interactions leading to pairing and effects selecting p and d waves are
thoroughly investigated. The role of transverse spin fluctuations is considered
using perturbation theory. Based on the results of the present study, we
discuss the pairing problem in the realistic t-J-like model. Possible
implications for preformed pairs formation and phase separation are drawn.Comment: 21 pages, 15 figure
Petrogenesis and Ni-Cu sulphide potential of mafic-ultramafic rocks in the Mesoproterozoic Fraser Zone within the Albany-Fraser Orogen, Western Australia
The Albany Fraser Orogen is located along the southern and southeastern margins of the Archean Yilgarn Craton. The orogen formed during reworking of the Yilgarn Craton, along with variable additions of juvenile mantle material, from at least 1810 Ma to 1140 Ma. The Fraser Zone is a 425 km long and 50 km wide geophysically distinct belt near the northwestern edge of the orogen, hosting abundant sills of predominantly metagabbroic non-cumulate rocks, but including larger cumulate bodies, all emplaced at c. 1300 Ma. The gabbroic rocks are interpreted to have crystallised from a basaltic magma that had âŒ8.8% MgO, 185 ppm Ni, 51 ppm Cu, and extremely low contents of platinum-group elements (PGE, <1 ppb). Levels of high field-strength elements (HFSE) in the least enriched rocks indicate that the magma was derived from a mantle source more depleted than a MORB source. Isotope and trace element systematics suggest that the magma was contaminated (ΔNd 0 to â2 throughout, La/Nb around 3) with small (<10%) amounts of crust before and during ascent and emplacement. Larger bodies of cumulate rocks show evidence for additional contamination, at the emplacement level, with country-rock metasedimentary rocks or their anatectic melts. The area has been the focus of considerable exploration for NiâCu sulphides following the discovery of the Nova deposit in 2012 in an intrusion consisting of olivine gabbronoritic, noritic and peridotitic cumulates, interlayered with metasedimentary rocks belonging to the Snowys Dam Formation of the Arid Basin. Disseminated sulphides from a drillcore intersecting the structurally upper portion of the intrusion, above the main ore zone, have tenors of âŒ3â6.3% Ni, 1.8â6% Cu and mostly <500 ppb PGE, suggesting derivation from magma with the same composition as the regional Fraser Zone metagabbroic sills, at R factors of âŒ1500. However, the Nova rocks tend to have higher ΔSr (38â52) and more variable ÎŽ34S (â2 to +4) than the regional metagabbros (ΔSr 17â32, ÎŽ34S around 0), consistent with the geochemical evidence for enhanced crustal assimilation of the metasedimentary country-rock in a relatively large magma staging chamber from which pulses of sulphide bearing, crystal-charged magmas were emplaced at slightly different crustal levels. Preliminary investigations suggest that the critical factors determining whether or not Fraser Zone mafic magmas are mineralised probably relate to local geodynamic conditions that allow large magma chambers to endure long enough to sequester country-rock sulphur
Single-hole properties in the - and strong-coupling models
We report numerical results for the single-hole properties in the -
model and the strong-coupling approximation to the Hubbard model in two
dimensions. Using the hopping basis with over states we discuss (for an
infinite system) the bandwidth, the leading Fourier coefficients in the
dispersion, the band masses, and the spin-spin correlations near the hole. We
compare our results with those obtained by other methods. The band minimum is
found to be at () for the - model for , and for the strong-coupling model for . The bandwidth
in both models is approximately at large , in rough agreement with
loop-expansion results but in disagreement with other results. The
strong-coupling bandwidth for t/J\agt6 can be obtained from the - model
by treating the three-site terms in first-order perturbation theory. The
dispersion along the magnetic zone face is flat, giving a large
parallel/perpendicular band mass ratio.Comment: 1 RevTeX file with epsf directives to include 8 .eps figures 8 figure
files encoded using uufile
- âŠ