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Tsvelik A.M.,Brookhaven National Laboratory
Physical Review Letters | Year: 2013

It is shown that a junction of three critical quantum Ising chains (Delta junction) can be described as a two-channel Kondo model with a spin S=1/2 localized at the junction, which is composed of the respective Ising, zero energy boundary Majorana modes. © 2013 American Physical Society.

Plant lignification is a tightly regulated complex cellular process that occurs via three sequential steps: the synthesis of monolignols within the cytosol; the transport of monomeric precursors across plasma membrane; and the oxidative polymerization of monolignols to form lignin macromolecules within the cell wall. Although we have a reasonable understanding of monolignol biosynthesis, many aspects of lignin assembly remain elusive. These include the precursors' transport and oxidation, and the initiation of lignin polymerization. This review describes our current knowledge of the molecular mechanisms underlying monolignol transport and oxidation, discusses the intriguing yet least-understood aspects of lignin assembly, and highlights the technologies potentially aiding in clarifying the enigma of plant lignification. © 2012 The Author Published by the Molecular Plant Shanghai Editorial Office in association with Oxford University Press on behalf of CSPB and IPPE, SIBS, CAS.

Gang O.,Brookhaven National Laboratory
Nature Materials | Year: 2012

Oleg Gang states that colloidal particles interacting through DNA linkers can be designed to form solids that melt when either heated or cooled. This scenario widens the temperature window in which colloidal superlattices form by reducing kinetic problems. One highly attractive aspect of DNA-based particle assembly is the ability to separate functional and structural requirements. The latest advancements have demonstrated more sophisticated constructs, such as DNA shells with tunable interactions, realized by varying the composition of two DNA strands on the shell and shells that can change structure and interactions through the incorporation of switchable and self-protected DNA strands. The bonding scheme proposed by Angioletti-Uberti and other researchers considers interparticle and intraparticle DNA hybridization. The scheme consists of two different DNA shells, including one with α and β strands, and another with α' β' strands.

Although the practice of protein engineering is industrially fruitful in creating biocatalysts and therapeutic proteins, applications of analogous techniques in the field of plant metabolic engineering are still in their infancy. Lignins are aromatic natural polymers derived from the oxidative polymerization of primarily three different hydroxycinnamyl alcohols, the monolignols. Polymerization of lignin starts with the oxidation of monolignols, followed by endwise cross-coupling of (radicals of) a monolignol and the growing oligomer/polymer. The para-hydroxyl of each monolignol is crucial for radical generation and subsequent coupling. Here, we describe the structure-function analysis and catalytic improvement of an artificial monolignol 4-O-methyltransferase created by iterative saturation mutagenesis and its use in modulating lignin and phenylpropanoid biosynthesis. We show that expressing the created enzyme in planta, thus etherifying the para-hydroxyls of lignin monomeric precursors, denies the derived monolignols any participation in the subsequent coupling process, substantially reducing lignification and, ultimately, lignin content. Concomitantly, the transgenic plants accumulated de novo synthesized 4-O-methylated soluble phenolics and wall-bound esters. The lower lignin levels of transgenic plants resulted in higher saccharification yields. Our study, through a structure-based protein engineering approach, offers a novel strategy for modulating phenylpropanoid/lignin biosynthesis to improve cell wall digestibility and diversify the repertories of biologically active compounds.

Tkachenko A.V.,Brookhaven National Laboratory
Physical Review Letters | Year: 2011

We present a theoretical analysis of the inverse problem in self-assembly. A particular scheme is proposed for building an arbitrary desired nanostructure out of self-assembled building blocks ("octopus" nanoparticles). The conditions for robust self-assembly of the target structure are identified. This includes the minimal number of "colors" needed to encode interparticle bonds, which are to be implemented as pairs of complementary DNA sequences. As a part of this analysis, it is demonstrated that a floppy network with thermal fluctuations, in a certain range of coordination numbers Z, possesses entropic rigidity and can be described as a traditional elastic solid. The onset of the entropic rigidity, Z=d+1, determines the minimal number of bond types per particle needed to encode the desired structure. Thermodynamic considerations give additional conditions for the implementation of this scheme. © 2011 American Physical Society.

Skokov V.,Brookhaven National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The phase structure of the Polyakov loop-extended chiral quark-meson model is explored in a nonperturbative approach, beyond a mean-field approximation, in the presence of a magnetic field. We show that by including meson fluctuations one cannot resolve the qualitative discrepancy on the dependence of the crossover transition temperature in a nonzero magnetic field between effective model predictions and recent lattice results. We compute the curvature of the crossover line in the T-μ B plane at a nonzero magnetic field and show that the curvature increases with increasing magnetic field. On the basis of QCD inequalities, we also argue that, at least in the large N c limit, a chiral critical end point and, consequently, a change from crossover to a first-order chiral phase transition are excluded at zero baryon chemical potential and nonzero magnetic field. © 2012 American Physical Society.

Sickles A.M.,Brookhaven National Laboratory
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

Recent measurements of particle correlations and the spectra of hadrons at both RHIC and the LHC are suggestive of hydrodynamic behavior in very small collision systems (p. +. Pb, d. +. Au and possibly high multiplicity p. +. p collisions at the LHC). The measurements in p. +. Pb and d. +. Au collisions are both qualitatively and quantitatively similar to what is seen in heavy ion collisions where low viscosity hot nuclear matter is formed. While light quarks and gluons are thought to make up the bulk matter, one of the most surprising results in heavy ion collisions is that charm quarks also have a large v2. Measurements of the transverse momentum spectra of electrons from the decay of D and B mesons in d. +. Au collisions show an enhancement in central collisions relative to p. +. p collisions. We employ the blast-wave model to determine if the flow of heavy quarks in d. +. Au and p. +. Pb collisions is able to explain the enhancement observed in the data. We find a reasonable description of the data with blast-wave parameters extracted from fits to the light hadron spectra, suggesting hydrodynamics as a possible explanation. © 2014 Elsevier B.V.

Fradkin E.,University of Illinois at Urbana - Champaign | Kivelson S.A.,Stanford University | Tranquada J.M.,Brookhaven National Laboratory
Reviews of Modern Physics | Year: 2015

The electronic phase diagrams of many highly correlated systems, and, in particular, the cuprate high temperature superconductors, are complex, with many different phases appearing with similar (sometimes identical) ordering temperatures even as material properties, such as dopant concentration, are varied over wide ranges. This complexity is sometimes referred to as "competing orders." However, since the relation is intimate, and can even lead to the existence of new phases of matter such as the putative "pair-density wave," the general relation is better thought of in terms of "intertwined orders." Some of the experiments in the cuprates which suggest that essential aspects of the physics are reflected in the intertwining of multiple orders, not just in the nature of each order by itself, are selectively analyzed. Several theoretical ideas concerning the origin and implications of this complexity are also summarized and critiqued. ©2015 American Physical Society.

Agency: Department of Energy | Branch: | Program: STTR | Phase: Phase II | Award Amount: 999.44K | Year: 2015

Proposed designs for a Future Circular Collider (FCC) to collide protons with a center-of-mass energy of 100 TeV call for dipoles with fields up to 20 Tesla (T). This is significantly beyond the present technology and requires using High Temperature Superconductors (HTS). The recent Particle Physics Project Prioritization Panel (P5), organized by the U.S. Department of Energy (DOE), strongly supports the U.S. maintaining its leadership in superconducting magnet technology. This STTR proposes to design, build, and test a proof-of-principle hybrid dipole that uses HTS in its highest-field regions and less-expensive low-temperature superconductors, Nb3Sn and NbTi, where they suffice. During Phase I, a coil block with ReBCO tape with Kapton insulation was fabricated and tested, confirming that winding had no measurable degradation. A major concern in the magnets built with ReBCO is the large field errors associated with the conductor magnetization in the tape geometry. The major discovery during Phase I was finding a solution to reduce those errors considerably. Based on this and work performed under previous SBIR/STTRs and other programs, HTS coils will be designed and built in Phase II and then integrated with the existing Nb3Sn common coil dipole. This provides a unique opportunity to test the concept in a proof-of-principle hybrid magnet with field approaching 15 T. A 20 T hybrid dipole design will also be developed with the goal of satisfying the requirements of accelerator magnets and reducing cost. Commercial Applications and Other Benefits: Since the cost of HTS superconductors is high and likely to remain so, it is important to minimize HTS usage. Commercial spin-offs in the areas of energy technologies (SMES, wind turbines), medical accelerators, security screening, and motors or generators for direct-drive wind turbines can be enabled by this technology, just as the development of NMR and MRI magnets was enabled by magnet R&D for previous generations of high-energy- physics accelerators. The knowledge gained from this program will provide valuable feedback to the conductor manufacturers in their efforts to improve these conductors to better meet the needs of the magnet community.

Kilgore W.B.,Brookhaven National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

I compute the contributions of the one-loop single-real-emission amplitudes, gg→Hg, qg→Hq, etc., to inclusive Higgs boson production through next-to-next-to-next-to-leading order (N3LO) in the strong coupling αs. The next-to-leading and next-to-next-to-leading order terms are computed in closed form, in terms of Γ functions and the hypergeometric functions F12 and F23. I compute the N3LO terms as Laurent expansions in the dimensional regularization parameter through order (μ1). To obtain the N3LO terms, I perform an extended threshold expansion of the phase space integrals and map the resulting coefficients onto a basis of harmonic polylogarithms. © 2014 American Physical Society.

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