14,664 research outputs found
Detection of sequential polyubiquitylation on a millisecond timescale
The pathway by which ubiquitin chains are generated on substrate through a cascade of enzymes consisting of an E1, E2 and E3 remains unclear. Multiple distinct models involving chain assembly on E2 or substrate have been proposed. However, the speed and complexity of the reaction have precluded direct experimental tests to distinguish between potential pathways. Here we introduce new theoretical and experimental methodologies to address both limitations. A quantitative framework based on product distribution predicts that the really interesting new gene (RING) E3 enzymes SCF^(Cdc4) and SCF^(ÎČ-TrCP) work with the E2 Cdc34 to build polyubiquitin chains on substrates by sequential transfers of single ubiquitins. Measurements with millisecond time resolution directly demonstrate that substrate polyubiquitylation proceeds sequentially. Our results present an unprecedented glimpse into the mechanism of RING ubiquitin ligases and illuminate the quantitative parameters that underlie the rate and pattern of ubiquitin chain assembly
Formation of diluted IIIâV nitride thin films by N ion implantation
iluted IIIâNââVâËâ alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1âyAs. In all three cases the fundamental band-gap energy for the ion beam synthesized IIIâNââVâËâ alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNâAs1âx and InNâPâËâalloys. In GaNâAsâËâ the highest value of x (fraction of âactiveâ substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850â°C. The highest value of x achieved in InNâPâËâ was higher, 0.012, and the NP was found to be stable to at least 850â°C. In addition, the N activation efficiency in implantedInNâPâËâ was at least a factor of 2 higher than that in GaNâAsâËâ under similar processing conditions. AlyGa1âyNâAsâËâ had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1âyNâAsâËâalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the ââPhotovoltaic Materials
Focus Areaââ in the DOE Center of Excellence for the Synthesis
and Processing of Advanced Materials, Office of Science,
Office of Basic Energy Sciences, Division of Materials
Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported
by Midwest Research Institute under subcontractor
No. AAD-9-18668-7 from NREL
Effect of Native Defects on Optical Properties of InxGa1-xN Alloys
The energy position of the optical absorption edge and the free carrier
populations in InxGa1-xN ternary alloys can be controlled using high energy
4He+ irradiation. The blue shift of the absorption edge after irradiation in
In-rich material (x > 0.34) is attributed to the band-filling effect
(Burstein-Moss shift) due to the native donors introduced by the irradiation.
In Ga-rich material, optical absorption measurements show that the
irradiation-introduced native defects are inside the bandgap, where they are
incorporated as acceptors. The observed irradiation-produced changes in the
optical absorption edge and the carrier populations in InxGa1-xN are in
excellent agreement with the predictions of the amphoteric defect model
Entanglement control in one-dimensional random XY spin chain
The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.Comment: 13 pages, 4 figure
Unconventional Spin Density Waves in Dipolar Fermi Gases
The conventional spin density wave (SDW) phase (Overhauser, 1962), as found
in antiferromagnetic metal for example (Fawcett 1988), can be described as a
condensate of particle-hole pairs with zero angular momentum, ,
analogous to a condensate of particle-particle pairs in conventional
superconductors. While many unconventional superconductors with Cooper pairs of
finite have been discovered, their counterparts, density waves with
non-zero angular momenta, have only been hypothesized in two-dimensional
electron systems (Nayak, 2000). Using an unbiased functional renormalization
group analysis, we here show that spin-triplet particle-hole condensates with
emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and
Lev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.
The order parameter of these exotic SDWs is a vector quantity in spin space,
and, moreover, is defined on lattice bonds rather than on lattice sites. We
determine the rich quantum phase diagram of dipolar fermions at half-filling as
a function of the dipolar orientation, and discuss how these SDWs arise amidst
competition with superfluid and charge density wave phases.Comment: 5 pages, 3 figure
The new two-way street of Chinese direct investment in the European Union
In the light of growing trade and investment flows, the investment relationship between the European Union (EU) and China needs to be revisited. Chinese firms face significant barriers in entering and operating in the European market whilst the European economy needs more investment. Support for investment may be crucial for both the EU and China to improve economic growth. The prospective International Investment Agreement (IIA) seeks to achieve this goal. This paper focuses on Chinese inward foreign direct investment into the EU and on the potential for generating greater mutual EUâChina flows, improved market access and investor protection under the IIA
The entanglement in one-dimensional random XY spin chain with Dzyaloshinskii-Moriya interaction
The impurities of exchange couplings, external magnetic fields and
Dzyaloshinskii--Moriya (DM) interaction considered as Gaussian distribution,
the entanglement in one-dimensional random spin systems is investigated by
the method of solving the different spin-spin correlation functions and the
average magnetization per spin. The entanglement dynamics at central locations
of ferromagnetic and antiferromagnetic chains have been studied by varying the
three impurities and the strength of DM interaction. (i) For ferromagnetic spin
chain, the weak DM interaction can improve the amount of entanglement to a
large value, and the impurities have the opposite effect on the entanglement
below and above critical DM interaction. (ii) For antiferromagnetic spin chain,
DM interaction can enhance the entanglement to a steady value. Our results
imply that DM interaction strength, the impurity and exchange couplings (or
magnetic field) play competing roles in enhancing quantum entanglement.Comment: 12 pages, 3 figure
Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating
Electrically controllable magnetism, which requires the field-effect
manipulation of both charge and spin degrees of freedom, has attracted growing
interests since the emergence of spintronics. In this work, we report the
reversible electrical switching of ferromagnetic (FM) states in platinum (Pt)
thin films by introducing paramagnetic ionic liquid (PIL) as the gating media.
The paramagnetic ionic gating controls the movement of ions with magnetic
moments, which induces itinerant ferromagnetism on the surface of Pt films with
large coercivity and perpendicular anisotropy mimicking the ideal
two-dimensional Ising-type FM state. The electrical transport of the induced FM
state shows Kondo effect at low temperature suggesting spatially separated
coexistence of Kondo scattering beneath the FM interface. The tunable FM state
indicates that paramagnetic ionic gating could serve as a versatile method to
induce rich transport phenomena combining field effect and magnetism at
PIL-gated interfaces.Comment: 17 pages, 4 figure
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