bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproducibility in the negative differential resistance characteristic of In0.17Al0.83N/GaN resonant tunneling diodes—Theoretical investigation
Authors: Chen Haoran , Yang Lin'an , Long Shuang , Hao Yue
Published: May 2013

We report on a simulation of gallium nitride (GaN) based resonant tunneling diode (RTD) at the Silvaco's ATLAS simulation platform with indium aluminum nitride (InAlN) as barrier layer. Results show that an excellent reproducibility of negative-differential-resistance (NDR) characteristic can be achieved when experimentally obtained deep-level trapping centers at the activation energy of 0.351 and 0.487 eV, respectively, are introduced into the polarized InAlN/GaN/InAlN quantum well. Theoretical analysis reveals that the lattice-matched InAlN/GaN heterostructure with stronger spontaneous polarization and weaker piezoelectric polarization can reduce the activation energy level of trapping centers, suppress the probability of ionization of the trapping centers, and therefore minimize the degradation of NDR characteristics, which demonstrates a potential application of the GaN-based RTD in terahertz regime.
Anharmonic state counts and partition functions for molecules via classical phase space integrals in curvilinear coordinates
Authors: Kamarchik Eugene , Jasper Ahren W.
Published: May 2013

An algorithm is presented for calculating fully anharmonic vibrational state counts, state densities, and partition functions for molecules using Monte Carlo integration of classical phase space. The algorithm includes numerical evaluations of the elements of the Jacobian and is general enough to allow for sampling in arbitrary curvilinear or rectilinear coordinate systems. Invariance to the choice of coordinate system is demonstrated for vibrational state densities of methane, where we find comparable sampling efficiency when using curvilinear z-matrix and rectilinear Cartesian normal mode coordinates. In agreement with past work, we find that anharmonicity increases the vibrational state density of methane by a factor of ∼2 at its dissociation threshold. For the vinyl radical, we find a significant (∼10×) improvement in sampling efficiency when using curvilinear z-matrix coordinates relative to Cartesian normal mode coordinates. We attribute this improved efficiency, in part, to a more natural curvilinear coordinate description of the double well associated with the H2C–C–H wagging motion. The anharmonicity correction for the vinyl radical state density is ∼1.4 at its dissociation threshold. Finally, we demonstrate that with trivial parallelizations of the Monte Carlo step, tractable calculations can be made for the vinyl radical using direct ab initio potential energy surface evaluations and a composite QCISD(T)/MP2 method.
On the comparisons between dissipative particle dynamics simulations and self-consistent field calculations of diblock copolymer microphase separation
Authors: Sandhu Paramvir , Zong Jing , Yang Delian , Wang Qiang
Published: May 2013

To highlight the importance of quantitative and parameter-fitting-free comparisons among different models/methods, we revisited the comparisons made by Groot and Madden [J. Chem. Phys. 108, 8713 (1998)10.1063/1.476300] and Chen et al. [J. Chem. Phys. 122, 104907 (2005)10.1063/1.1860351] between their dissipative particle dynamics (DPD) simulations of the DPD model and the self-consistent field (SCF) calculations of the “standard” model done by Matsen and Bates [Macromolecules 29, 1091 (1996)10.1021/ma951138i] for diblock copolymer (DBC) A-B melts. The small values of the invariant degree of polymerization used in the DPD simulations do not justify the use of the fluctuation theory of Fredrickson and Helfand [J. Chem. Phys. 87, 697 (1987)10.1063/1.453566] by Groot and Madden, and their fitting between the DPD interaction parameters and the Flory-Huggins χ parameter in the “standard” model also has no rigorous basis. Even with their use of the fluctuation theory and the parameter-fitting, we do not find the “quantitative match” for the order-disorder transition of symmetric DBC claimed by Groot and Madden. For lamellar and cylindrical structures, we find that the system fluctuations/correlations decrease the bulk period and greatly suppress the large depletion of the total segmental density at the A-B interfaces as well as its oscillations in A- and B-domains predicted by our SCF calculations of the DPD model. At all values of the A-block volume fractions in the copolymer f (which are integer multiples of 0.1), our SCF calculations give the same sequence of phase transitions with varying χN as the “standard” model, where N denotes the number of segments on each DBC chain. All phase boundaries, however, are shifted to higher χN due to the finite interaction range in the DPD model, except at f = 0.1 (and 0.9), where χN at the transition between the disordered phase and the spheres arranged on a body-centered cubic lattice is lower due to N = 10 in the DPD model. Finally, in 11 of the total 20 cases (f-χN combinations) studied in the DPD simulations, a morphology different from the SCF prediction was obtained due to the differences between these two methods.
Electrophoretic mobility reversal of polyampholytes induced by strong electric fields or confinement
Authors: Hickey Owen A. , Holm Christian
Published: May 2013

We investigate the mobility of polyampholytes consisting of both negatively and positively charged sections. The simulations are carried out using molecular dynamics simulations with electrohydrodynamical effects taken into account via a simple coupling scheme to a lattice-Boltzmann fluid. Our results show a previously predicted mobility reversal of the polyampholytes as the applied electric field is increased due to stretching of the polyampholytes. Further, we show that a similar mobility reversal can be induced due to confinement between parallel plates. At high electric field strengths, the polyampholytes’ electrophoretic mobility is a non-monotonic function of the distance between the plates. These results help to clarify the role of deformation and confinement on the electrophoretic mobility of polyampholytes.
Theoretical prediction of rare gas inserted hydronium ions: HRgOH2+
Authors: Ghosh Ayan , Manna Debashree , Ghanty Tapan K.
Published: May 2013

A possibility of existence of new species through insertion of a rare gas atom in hydronium ion resulting into HRgOH2+ cation (Rg = He, Ar, Kr, and Xe) has been explored by using various ab initio quantum chemical techniques. Structure, harmonic vibrational frequencies, stability, and charge distribution of HRgOH2+ species as obtained using density functional theory, second order Møller-Plesset perturbation theory, and coupled-cluster theory based methods are reported in this work. All the calculated results suggest that the HRgOH2+ species are stable enough with respect to all the dissociation channels, except the 2-body dissociation path (H3O+ + Rg). Nevertheless, this 2-body dissociation channel connected through the relevant transition state is associated with a finite barrier, which in turn would prevent the metastable species in transforming to global minimum products. The calculated values of topological properties within the framework of quantum theory of atoms-in-molecules are found to be consistent with the bond length values. Structural and energetic parameters clearly suggest that it might be possible to prepare and characterize the HRgOH2+ species (except HHeOH2+) using electron bombardment matrix isolation technique in a way similar to that of the preparation of (Rg2H)+ or mixed (RgHRg′)+ cations.
Confined Brownian ratchets
Authors: Malgaretti Paolo , Pagonabarraga Ignacio , Rubi J. Miguel
Published: May 2013

We analyze the dynamics of Brownian ratchets in a confined environment. The motion of the particles is described by a Fick-Jakobs kinetic equation in which the presence of boundaries is modeled by means of an entropic potential. The cases of a flashing ratchet, a two-state model, and a ratchet under the influence of a temperature gradient are analyzed in detail. We show the emergence of a strong cooperativity between the inherent rectification of the ratchet mechanism and the entropic bias of the fluctuations caused by spatial confinement. Net particle transport may take place in situations where none of those mechanisms leads to rectification when acting individually. The combined rectification mechanisms may lead to bidirectional transport and to new routes to segregation phenomena. Confined Brownian ratchets could be used to control transport in mesostructures and to engineer new and more efficient devices for transport at the nanoscale.
Assessment of range-separated time-dependent density-functional theory for calculating C6 dispersion coefficients
Authors: Toulouse Julien , Rebolini Elisa , Gould Tim , Dobson John F. , Seal Prasenjit , Ángyán János G.
Published: May 2013

We assess a variant of linear-response range-separated time-dependent density-functional theory (TDDFT), combining a long-range Hartree-Fock (HF) exchange kernel with a short-range adiabatic exchange-correlation kernel in the local-density approximation (LDA) for calculating isotropic C6 dispersion coefficients of homodimers of a number of closed-shell atoms and small molecules. This range-separated TDDFT tends to give underestimated C6 coefficients of small molecules with a mean absolute percentage error of about 5%, a slight improvement over standard TDDFT in the adiabatic LDA which tends to overestimate them with a mean absolute percentage error of 8%, but close to time-dependent Hartree-Fock which has a mean absolute percentage error of about 6%. These results thus show that introduction of long-range HF exchange in TDDFT has a small but beneficial impact on the values of C6 coefficients. It also confirms that the present variant of range-separated TDDFT is a reasonably accurate method even using only a LDA-type density functional and without adding an explicit treatment of long-range correlation.
Triezenberg-Zwanzig expression for the surface tension of a liquid drop
Authors: Blokhuis Edgar M.
Published: May 2013

Formulas, analogous to the Triezenberg-Zwanzig expression for the surface tension of a planar interface, are presented for the Tolman length, the bending rigidity, and the rigidity constant associated with Gaussian curvature. These expressions feature the Ornstein-Zernike direct correlation function and are derived from considering the deformation of a liquid drop in the presence of an external field. This approach is in line with the original analysis by Yvon [in Proceedings of the IUPAP Symposium on Thermodynamics, Brussels, 1948]. It is shown that our expressions reduce to previous results from density functional theory when a mean-field approximation is made for the direct correlation function. We stress the importance of the form of the external field used and show how the values of the rigidity constants depend on it.
Spatial ordering due to hydrodynamic interactions between a pair of colliding drops in a confined shear
Authors: Sarkar Kausik , Singh Rajesh Kumar
Published: May 2013

Pair-collision between viscous drops in a confined shear is simulated to show that the confinement alters the trajectories of the drops spatially ordering them at a finite separation in the center of the domain. In contrast to free shear where drops eventually adopt free streamlines with a finite cross-stream separation, here they move towards the centerline achieving zero cross-stream separation but a net stream-wise separation. The latter varies as inverse of capillary number and cube of the confinement (distance between the walls). The final stream-wise separation does not depend on the initial positions of the drops when the drops are in the same shear plane. The separation decreases approximately linearly with the initial separation in the vorticity direction. An analytical theory explaining the phenomenon is presented. Effects of the ratio of drop to matrix viscosity are briefly investigated.
Two-beam spin noise spectroscopy
Authors: Pershin Yuriy V. , Slipko Valeriy A. , Roy Dibyendu , Sinitsyn Nikolai A.
Published: May 2013

We propose a method of two-beam spin noise spectroscopy to test the spin transport at equilibrium via analysis of correlations between time-shifted spin fluctuations at different space locations. This method allows one to determine the strength of spin-orbit interaction and spin relaxation time and separate spin noise of conducting electrons from the background noise of localized electrons. We formulate a theory of two-beam spin noise spectroscopy in semiconductor wires with Bychkov-Rashba spin-orbit interaction taking into account several possible spin relaxation channels and finite size of laser beams. Our theory predicts a peak shift with respect to the Larmor frequency to higher or lower frequencies depending on the strength of spin orbit interaction and distance between the beams. The two-beam spin noise spectroscopy could find applications in experimental studies of semiconductors, emergent materials, and many other systems.
Nanodiamond vacuum field emission device with gate modulated triode characteristics
Authors: Hsu S. H. , Kang W. P. , Raina S. , Huang J. H.
Published: May 2013

A three-electrode nanodiamond vacuum field emission (VFE) device with gate modulated triode characteristics is developed by integrating nanodiamond emitter with self-aligned silicon gate and anode, employing a mold transfer technique in conjunction with chemical vapor deposition of nanodiamond. Triode behavior showing emission current modulation with high current density at low operating voltages is achieved. A systematic analysis based on modified Fowler-Nordheim theory is used to analyze gate modulated VFE characteristics, confirming the triode field emission mechanism and operating principle. The realization of an efficient VFE microtriode has achieved the fundamental step for further development of vacuum integrated microelectronics.
Exchange bias in thin Heusler alloy films in contact with antiferromagnet
Authors: Dubowik J. , Gościańska I. , Załȩski K. , Głowiński H. , Kudryavtsev Y. , Ehresmann A.
Published: May 2013

Exchange bias is studied in thin film systems, in which three types of Heusler alloys (Ni2MnSn, Co2MnSn, and Co2FeSi) are in contact with an antiferromagnet. Magnetic exchange interactions between the constituting atoms (i.e., Ni-Mn, Mn-Mn, Co-Mn, and Co-Fe, or Co-Co) differ substantially in these Heusler alloys. We explain the influence of the exchange stiffness A within the Heusler alloys and of the exchange coupling between Heusler alloy and an antiferromagnet in a finite interface volume. Insertion of an ultrathin Co layer at interfaces brings about an enhancement of the exchange bias in Heusler alloy/antiferromagnet layer system.
The first-principles study of oscillating rectifying performance in nanoribbon-chain-carbon nanotube junctions
Authors: Qiu Ming , Liew K. M.
Published: May 2013

Electronic transport properties of armchair graphene nanoribbon and capped carbon nanotube junctions, covalently bridged by carbon atomic chains with different numbers of carbon atoms, are investigated. The first-principles calculations based on non-equilibrium Green's functions with the density-functional theory show that their I-V characteristics display odd-even effects and rectifying behaviors show obvious oscillations, namely, different bond patterns for even- and odd-numbered carbon chains affect the contact bonds, charge transfer, density of states, evolutions of molecular orbitals, and rectifying performance.
Laser produced plasma sources for nanolithography—Recent integrated simulation and benchmarking
Authors: Hassanein A. , Sizyuk T.
Published: May 2013

Photon sources for extreme ultraviolet lithography (EUVL) are still facing challenging problems to achieve high volume manufacturing in the semiconductor industry. The requirements for high EUV power, longer optical system and components lifetime, and efficient mechanisms for target delivery have narrowed investigators towards the development and optimization of dual-pulse laser sources with high repetition rate of small liquid tin droplets and the use of multi-layer mirror optical system for collecting EUV photons. We comprehensively simulated laser-produced plasma sources in full 3D configuration using 10–50 μm tin droplet targets as single droplets as well as, for the first time, distributed fragmented microdroplets with equivalent mass. The latter is to examine the effects of droplet fragmentation resulting from the first pulse and prior to the incident second main laser pulse. We studied the dependence of target mass and size, laser parameters, and dual pulse system configuration on EUV radiation output and on atomic and ionic debris generation. Our modeling and simulation included all phases of laser target evolution: from laser/droplet interaction, energy deposition, target vaporization, ionization, plasma hydrodynamic expansion, thermal and radiation energy redistribution, and EUV photons collection as well as detail mapping of photons source size and location. We also simulated and predicted the potential damage to the optical mirror collection system from plasma thermal and energetic debris and the requirements for mitigating systems to reduce debris fluence. The debris effect on mirror collection system is analyzed using our three-dimensional ITMC-DYN Monte Carlo package. Modeling results were benchmarked against our CMUXE laboratory experimental studies for the EUV photons production and for debris and ions generation.
Generation of high-flux attosecond extreme ultraviolet continuum with a 10 TW laser
Authors: Wu Y. , Cunningham E. , Zang H. , Li J. , Chini M. , Wang X. , Wang Y. , Zhao K. , Chang Z.
Published: May 2013

We report a laser system that delivers 15 fs pulses with 200 mJ energy at a 10 Hz repetition rate. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two-stage Ti:sapphire chirped-pulse power amplifier with sub-mJ white-light pulses from a gas-filled hollow-core fiber. With this laser, an extreme ultraviolet (XUV) super-continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The XUV pulse energy was ∼100 nJ at the exit of the argon gas target.
Scaling law for energy bandgap and effective electron mass in graphene nano mesh
Authors: Lee Jonghoon , Roy Ajit K. , Wohlwend Jennifer L. , Varshney Vikas , Ferguson John B. , Mitchel William C. , Farmer Barry L.
Published: May 2013

For the energy bandgap of semiconducting graphene nano mesh (GNM), chirality dependent scaling rules have been proposed so far. Based on extensive tight binding studies and simple geometric arguments, we report that Pedersen scaling governs not only the energy bandgap but also the effective mass of the Bloch electron of the semiconducting GNM regardless of its chirality or the crystallography of the mesh holes when the hole areal fraction is low.
Gold-titania interface toughening and thermal conductance enhancement using an organophosphonate nanolayer
Authors: Chow Philippe K. , Cardona Quintero Y. , O'Brien Peter , Hubert Mutin P. , Lane Michael , Ramprasad R. , Ramanath Ganpati
Published: May 2013

We demonstrate that a mercaptan-terminated organophosphonate nanolayer at gold-titania interfaces can give rise to two- to three-fold enhancement in the interfacial fracture toughness and thermal conductance. Electron spectroscopy reveals that interfacial delamination occurs at the metal-molecule interface near the gold-sulfur bonds, consistent with density functional theory calculations of bond energies. Qualitative correlation between interfacial fracture toughness and bond energies suggest that organophosphonate nanolayers are resilient to humidity-induced degradation. These results, and the versatility of organophosphonates as surface functionalization agents for technologically relevant materials, unlock uncharted avenues for molecular engineering of interfaces in materials and devices for a variety of applications.
Simulations of magnetic hysteresis loops for dual layer recording media
Authors: Fal T. J. , Plumer M. L. , Whitehead J. P. , Mercer J. I. , van Ek J. , Srinivasan K.
Published: May 2013

A Kinetic Monte-Carlo algorithm is applied to examine MH loops of dual-layer magnetic recording media at finite temperature and long time scales associated with typical experimental measurements. In contrast with standard micromagnetic simulations, which are limited to the ns-μs time regime, our approach allows for the direct calculation of magnetic configurations over periods from minutes to years. The model is used to fit anisotropy and coupling parameters to experimental data on exchange-coupled composite media which are shown to deviate significantly from standard micromagnetic results. Sensitivities of the loops to anisotropy, inter-layer exchange coupling, temperature, and sweep rate are examined.
Stimulated Raman scattering cascade spanning the wavelength range of 523 to 1750 nm using a graded-index multimode optical fiber
Authors: Pourbeyram Hamed , Agrawal Govind P. , Mafi Arash
Published: May 2013

We report on the generation of a Raman cascade spanning the wavelength range of 523 to 1750 nm wavelength range in a standard telecommunication graded-index multimode optical fiber. Despite the highly multimode nature of the pump, the Raman peaks are generated in specific modes of the fiber, confirming substantial beam cleanup during the stimulated Raman scattering process.
Large surface-enhanced Raman scattering from self-assembled gold nanosphere monolayers
Authors: Fontana Jake , Livenere John , Bezares Francisco J. , Caldwell Joshua D. , Rendell Ronald , Ratna Banahalli R.
Published: May 2013

We demonstrate an average surface-enhanced Raman scattering enhancement on the order of 108 from benzenethiol molecules using self-assembled, macroscopic, and tunable gold nanosphere monolayers on non-templated substrates. The self-assembly of the nanosphere monolayers uses a simple and efficient technique that allows for the creation of a high-density, chemically functionalized gold nanosphere monolayers with enhancement factors comparable to those produced using top-down fabrication techniques. These films may provide an approach for the future development of portable chemical/biological sensors.
Behavioural, follicular and hormonal characteristics of the oestrous cycle of Mexican Criollo cattle
Authors: Quezada-Casasola A. , Avendaño-Reyes L. , Ramírez-Godínez J. A. , Macías-Cruz U. , Correa-Calderón A.
Published: May 2013

The objective of the present study was to describe the behavioural, ovarian and hormonal characteristics of the oestrous cycle of Criollo cattle. Twenty-two cycling cows subjected to oestrus synchronisation were used to take blood samples every 4 h, to determine luteinising hormone (LH) until ovulation was detected by ultrasound and then every 24 h until the subsequent naturally occurring ovulation to determine progesterone concentrations. At the onset of synchronised oestrus, ovaries were examined by ultrasound every 8 h to determine dominant follicles until ovulation was detected, and daily afterwards to observe ovarian dynamics until the onset of the subsequent spontaneous behavioural oestrus. Time from oestrus to ovulation was higher in synchronised than in spontaneous oestrus (P < 0.01). Time from LH surge to ovulation was 40.5 h. When two- and three-wave cycles were compared, inter-ovulatory intervals were similar, growth rate of the preovulatory follicle was lower in two-wave cycles, time from onset of ovulatory wave to ovulation was higher in cycles with two waves and time from oestrus to ovulation was higher in three-wave cycles (P < 0.01). Corpus luteum volume averaged 1.3 cm3 and progesterone concentration peaked at an average 6.5 ng/mL. LH peak averaged 33.5 ng/mL during oestrus in all cows. Ovulatory follicle diameter ranged from 8 to 12 mm in either two- or three-wave cycles. Results suggested that overall times from oestrus and LH peak to ovulation are longer in Criollo cows than those in other breeds. This, along with information about growth rate, size and age of ovulatory follicles, may have implications for reviewing the optimum time for artificial insemination and how reproductive technologies are applied to Criollo cattle.
Release Kinetics of 6-Mercaptopurine and 6-Thioguanine from Bioinspired Core-Crosslinked Thymine Functionalised Polymeric Micelles
Authors: Kaur Gagan , Hearn Milton T. W. , Bell Toby D. M. , Saito Kei
Published: May 2013

A bioinspired core-bound polymeric micellar system based on hydrogen bonding and photo-crosslinking of thymine has been prepared from the amphiphilic block copolymers, poly(vinylbenzylthymine)-block-poly(vinylbenzyltriethylammonium chloride). The chemical loading and controlled release potential of these micelles was investigated using two drugs, 6-mercaptopurine and 6-thioguanine. The release kinetics of drug-loaded polymeric micelles was determined by pressure ultrafiltration and the effects of hydrogen bonding, core-crosslinking, and core size on the loading capacity and release kinetics were analysed. The results demonstrate that drug release rates are affected by hydrogen bonding in the micelle core. Furthermore, these studies indicate that drug release rates can be controlled by changing the size of the core and by photo-crosslinking thymine groups in the core.
Adaptive governance and institutional strategies for climate-induced community relocations in Alaska
Authors: Bronen Robin , Chapin F. Stuart
Published: May 2013

This article presents governance and institutional strategies for climate-induced community relocations. In Alaska, repeated extreme weather events coupled with climate change-induced coastal erosion impact the habitability of entire communities. Community residents and government agencies concur that relocation is the only adaptation strategy that can protect lives and infrastructure. Community relocation stretches the financial and institutional capacity of existing governance institutions. Based on a comparative analysis of three Alaskan communities, Kivalina, Newtok, and Shishmaref, which have chosen to relocate, we examine the institutional constraints to relocation in the United States. We identify policy changes and components of a toolkit that can facilitate community-based adaptation when environmental events threaten people’s lives and protection in place is not possible. Policy changes include amendment of the Stafford Act to include gradual geophysical processes, such as erosion, in the statutory definition of disaster and the creation of an adaptive governance framework to allow communities a continuum of responses from protection in place to community relocation. Key components of the toolkit are local leadership and integration of social and ecological well-being into adaptation planning.
Entropy-driven crystal formation on highly strained substrates
Authors: Savage John R. , Hopp Stefan F. , Ganapathy Rajesh , Gerbode Sharon J. , Heuer Andreas , Cohen Itai
Published: May 2013

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing. In contrast, less is understood about how mismatch affects crystallization of larger particles, such as globular proteins and nanoparticles, where interparticle interaction energies are often comparable to thermal fluctuations and are short ranged, extending only a fraction of the particle size. Here, using colloidal experiments and simulations, we find particles with short-range attractive interactions form crystals on isotropically strained lattices with spacings significantly larger than the interaction length scale. By measuring the free-energy cost of dimer formation on monolayers of increasing uniaxial strain, we show the underlying mismatched substrate mediates an entropy-driven attractive interaction extending well beyond the interaction length scale. Remarkably, because this interaction arises from thermal fluctuations, lowering temperature causes such substrate-mediated attractive crystals to dissolve. Such counterintuitive results underscore the crucial role of entropy in heteroepitaxy in this technologically important regime. Ultimately, this entropic component of lattice mismatched crystal growth could be used to develop unique methods for heterogeneous nucleation and growth of single crystals for applications ranging from protein crystallization to controlling the assembly of nanoparticles into ordered, functional superstructures. In particular, the construction of substrates with spatially modulated strain profiles would exploit this effect to direct self-assembly, whereby nucleation sites and resulting crystal morphology can be controlled directly through modifications of the substrate.
Polysaccharide chemistry regulates kinetics of calcite nucleation through competition of interfacial energies
Authors: Giuffre Anthony J. , Hamm Laura M. , Han Nizhou , De Yoreo James J. , Dove Patricia M.
Published: May 2013

Calcified skeletons are produced within complex assemblages of proteins and polysaccharides whose roles in mineralization are not well understood. Here we quantify the kinetics of calcite nucleation onto a suite of high-purity polysaccharide (PS) substrates under controlled conditions. The energy barriers to nucleation are PS-specific by a systematic relationship to PS charge density and substrate structure that is rooted in minimization of the competing substrate–crystal and substrate–liquid interfacial energies. Chitosan presents a low-energy barrier to nucleation because its near-neutral charge favors formation of a substrate–crystal interface, thus reducing substrate interactions with water. Progressively higher barriers are measured for negatively charged alginates and heparin that favor contact with the solution over the formation of new substrate–crystal interfaces. The findings support a directing role for PS in biomineral formation and demonstrate that substrate–crystal interactions are one end-member in a larger continuum of competing forces that regulate heterogeneous crystal nucleation.
Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature
Authors: Ershov Dmitry , Sprakel Joris , Appel Jeroen , Cohen Stuart Martien A. , van der Gucht Jasper
Published: May 2013

Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometer-sized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature that is also anisotropic. In that case, the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature.
NF-κB inhibits osteogenic differentiation of mesenchymal stem cells by promoting β-catenin degradation
Authors: Chang Jia , Liu Fei , Lee Min , Wu Benjamin , Ting Kang , Zara Janette N. , Soo Chia , Al Hezaimi Khalid , Zou Weiping , Chen Xiaohong , Mooney David J. , Wang Cun-Yu
Published: May 2013

Mesenchymal stem cell (MSC)-based transplantation is a promising therapeutic approach for bone regeneration and repair. In the realm of therapeutic bone regeneration, the defect or injured tissues are frequently inflamed with an abnormal expression of inflammatory mediators. Growing evidence suggests that proinflammatory cytokines inhibit osteogenic differentiation and bone formation. Thus, for successful MSC-mediated repair, it is important to overcome the inflammation-mediated inhibition of tissue regeneration. In this study, using genetic and chemical approaches, we found that proinflammatory cytokines TNF and IL-17 stimulated IκB kinase (IKK)–NF-κB and impaired osteogenic differentiation of MSCs. In contrast, the inhibition of IKK–NF-κB significantly enhanced MSC-mediated bone formation. Mechanistically, we found that IKK–NF-κB activation promoted β-catenin ubiquitination and degradation through induction of Smurf1 and Smurf2. To translate our basic findings to potential clinic applications, we showed that the IKK small molecule inhibitor, IKKVI, enhanced osteogenic differentiation of MSCs. More importantly, the delivery of IKKVI promoted MSC-mediated craniofacial bone regeneration and repair in vivo. Considering the well established role of NF-κB in inflammation and infection, our results suggest that targeting IKK–NF-κB may have dual benefits in enhancing bone regeneration and repair and inhibiting inflammation, and this concept may also have applicability in many other tissue regeneration situations.
Visual arrestin interaction with clathrin adaptor AP-2 regulates photoreceptor survival in the vertebrate retina
Authors: Moaven Hormoz , Koike Yukihiro , Jao Christine C. , Gurevich Vsevolod V. , Langen Ralf , Chen Jeannie
Published: May 2013

Arrestins bind ligand-activated, phosphorylated G protein-coupled receptors (GPCRs) and terminate the activation of G proteins. Additionally, nonvisual arrestin/GPCR complex can initiate G protein-independent intracellular signals through their ability to act as scaffolds that bring other signaling molecules to the internalized GPCR. Like nonvisual arrestins, vertebrate visual arrestin (ARR1) terminates G protein signaling from light-activated, phosphorylated GPCR, rhodopsin. Unlike nonvisual arrestins, its role as a transducer of signaling from internalized rhodopsin has not been reported in the vertebrate retina. Formation of signaling complexes with arrestins often requires recruitment of the endocytic adaptor protein, AP-2. We have previously shown that Lys296 → Glu (K296E), which is a naturally occurring rhodopsin mutation in certain humans diagnosed with autosomal dominant retinitis pigmentosa, causes toxicity through forming a stable complex with ARR1. Here we investigated whether recruitment of AP-2 by the K296E/ARR1 complex plays a role in generating the cell death signal in a transgenic mouse model of retinal degeneration. We measured the binding affinity of ARR1 for AP-2 and found that, although the affinity is much lower than that of the other arrestins, the unusually high concentration of ARR1 in rods would favor this interaction. We further demonstrate that p44, a splice variant of ARR1 that binds light-activated, phosphorylated rhodopsin but lacks the AP-2 binding motif, prevents retinal degeneration and rescues visual function in K296E mice. These results reveal a unique role of ARR1 in a G protein-independent signaling cascade in the vertebrate retina.
Nematic liquid crystal boojums with handles on colloidal handlebodies
Authors: Liu Qingkun , Senyuk Bohdan , Tasinkevych Mykola , Smalyukh Ivan I.
Published: May 2013

Topological defects that form on surfaces of ordered media, dubbed boojums, are ubiquitous in superfluids, liquid crystals (LCs), Langmuir monolayers, and Bose–Einstein condensates. They determine supercurrents in superfluids, impinge on electrooptical switching in polymer-dispersed LCs, and mediate chemical response at nematic-isotropic fluid interfaces, but the role of surface topology in the appearance, stability, and core structure of these defects remains poorly understood. Here, we demonstrate robust generation of boojums by controlling surface topology of colloidal particles that impose tangential boundary conditions for the alignment of LC molecules. To do this, we design handlebody-shaped polymer particles with different genusg. When introduced into a nematic LC, these particles distort the nematic molecular alignment field while obeying topological constraints and induce at least 2g− 2 boojums that allow for topological charge conservation. We characterize 3D textures of boojums using polarized nonlinear optical imaging of molecular alignment and explain our findings by invoking symmetry considerations and numerical modeling of experiment-matching director fields, order parameter variations, and nontrivial handle-shaped core structure of defects. Finally, we discuss how this interplay between the topologies of colloidal surfaces and boojums may lead to controlled self-assembly of colloidal particles in nematic and paranematic hosts, which, in turn, may enable reconfigurable topological composites.
Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago
Authors: Wittke James H. , Weaver James C. , Bunch Ted E. , Kennett James P. , Kennett Douglas J. , Moore Andrew M. T. , Hillman Gordon C. , Tankersley Kenneth B. , Goodyear Albert C. , Moore Christopher R. , Daniel I. Randolph , Ray Jack H. , Lopinot Neal H. , Ferraro David , Israde-Alcántara Isabel , Bischoff James L. , DeCarli Paul S. , Hermes Robert E. , Kloosterman Johan B. , Revay Zsolt , Howard George A. , Kimbel David R. , Kletetschka Gunther , Nabelek Ladislav , Lipo Carl P. , Sakai Sachiko , West Allen , Firestone Richard B.
Published: May 2013

Significance

We present detailed geochemical and morphological analyses of nearly 700 spherules from 18 sites in support of a major cosmic impact at the onset of the Younger Dryas episode (12.8 ka). The impact distributed ∼10 million tonnes of melted spherules over 50 million square kilometers on four continents. Origins of the spherules by volcanism, anthropogenesis, authigenesis, lightning, and meteoritic ablation are rejected on geochemical and morphological grounds. The spherules closely resemble known impact materials derived from surficial sediments melted at temperatures >2,200 °C. The spherules correlate with abundances of associated melt-glass, nanodiamonds, carbon spherules, aciniform carbon, charcoal, and iridium.
Preventing Alzheimer’s disease-related gray matter atrophy by B-vitamin treatment
Authors: Douaud Gwenaëlle , Refsum Helga , de Jager Celeste A. , Jacoby Robin , E. Nichols Thomas , Smith Stephen M. , Smith A. David
Published: May 2013

Is it possible to prevent atrophy of key brain regions related to cognitive decline and Alzheimer’s disease (AD)? One approach is to modify nongenetic risk factors, for instance by lowering elevated plasma homocysteine using B vitamins. In an initial, randomized controlled study on elderly subjects with increased dementia risk (mild cognitive impairment according to 2004 Petersen criteria), we showed that high-dose B-vitamin treatment (folic acid 0.8 mg, vitamin B6 20 mg, vitamin B12 0.5 mg) slowed shrinkage of the whole brain volume over 2 y. Here, we go further by demonstrating that B-vitamin treatment reduces, by as much as seven fold, the cerebral atrophy in those gray matter (GM) regions specifically vulnerable to the AD process, including the medial temporal lobe. In the placebo group, higher homocysteine levels at baseline are associated with faster GM atrophy, but this deleterious effect is largely prevented by B-vitamin treatment. We additionally show that the beneficial effect of B vitamins is confined to participants with high homocysteine (above the median, 11 µmol/L) and that, in these participants, a causal Bayesian network analysis indicates the following chain of events: B vitamins lower homocysteine, which directly leads to a decrease in GM atrophy, thereby slowing cognitive decline. Our results show that B-vitamin supplementation can slow the atrophy of specific brain regions that are a key component of the AD process and that are associated with cognitive decline. Further B-vitamin supplementation trials focusing on elderly subjets with high homocysteine levels are warranted to see if progression to dementia can be prevented.
Sustained accurate recording of intracellular acidification in living tissues with a photo-controllable bioluminescent protein
Authors: Hattori Mitsuru , Haga Sanae , Takakura Hideo , Ozaki Michitaka , Ozawa Takeaki
Published: May 2013

Regulation of an intracellular acidic environment plays a pivotal role in biological processes and functions. However, spatiotemporal analysis of the acidification in complex tissues of living subjects persists as an important challenge. We developed a photo-inactivatable bioluminescent indicator, based on a combination of luciferase-fragment complementation and a photoreaction of a light, oxygen, and voltage domain fromAvena sativaPhototropin1 (LOV2), to visualize temporally dynamic acidification in living tissue samples. Bioluminescence of the indicator diminished upon light irradiation and it recovered gradually in the dark state thereafter. The recovery rate was remarkably sensitive to pH changes but unsusceptible to fluctuation of luciferin or ATP concentrations. Bioluminescence imaging, taken as an index of the recovery rates, enabled long-time recording of acidification in apoptotic and autophagous processes in a cell population and an ischemic condition in living mice. This technology using the indicator is widely applicable to sense organelle-specific acidic changes in target biological tissues.
Anti-CD47 antibody–mediated phagocytosis of cancer by macrophages primes an effective antitumor T-cell response
Authors: Tseng Diane , Volkmer Jens-Peter , Willingham Stephen B. , Contreras-Trujillo Humberto , Fathman John W. , Fernhoff Nathaniel B. , Seita Jun , Inlay Matthew A. , Weiskopf Kipp , Miyanishi Masanori , Weissman Irving L.
Published: May 2013

Mobilization of the T-cell response against cancer has the potential to achieve long-lasting cures. However, it is not known how to harness antigen-presenting cells optimally to achieve an effective antitumor T-cell response. In this study, we show that anti-CD47 antibody–mediated phagocytosis of cancer by macrophages can initiate an antitumor T-cell immune response. Using the ovalbumin model antigen system, anti-CD47 antibody–mediated phagocytosis of cancer cells by macrophages resulted in increased priming of OT-I T cells [cluster of differentiation 8-positive (CD8+)] but decreased priming of OT-II T cells (CD4+). The CD4+T-cell response was characterized by a reduction in forkhead box P3-positive (Foxp3+) regulatory T cells. Macrophages following anti-CD47–mediated phagocytosis primed CD8+T cells to exhibit cytotoxic function in vivo.This response protected animals from tumor challenge. We conclude that anti-CD47 antibody treatment not only enables macrophage phagocytosis of cancer but also can initiate an antitumor cytotoxic T-cell immune response.
Deliberate reduction of hemagglutinin and neuraminidase expression of influenza virus leads to an ultraprotective live vaccine in mice
Authors: Yang Chen , Skiena Steven , Futcher Bruce , Mueller Steffen , Wimmer Eckard
Published: May 2013

A long-held dogma posits that strong presentation to the immune system of the dominant influenza virus glycoprotein antigens neuraminidase (NA) and hemagglutinin (HA) is paramount for inducing protective immunity against influenza virus infection. We have deliberately violated this dogma by constructing a recombinant influenza virus strain of A/PR8/34 (H1N1) in which expression of
NA
and
HA
genes was suppressed. We down-regulated NA and HA expression by recoding the respective genes with suboptimal codon pair bias, thereby introducing hundreds of nucleotide changes while preserving their codon use and protein sequence. The variants PR8-NA
Min
, PR8-HA
Min
, and PR8-(NA+HA)
Min
(Min, minimal expression) were used to assess the contribution of reduced glycoprotein expression to growth in tissue culture and pathogenesis in BALB/c mice. All three variants proliferated in Madin–Darby canine kidney cells to nearly the degree as WT PR8. In mice, however, they expressed explicit attenuation phenotypes, as revealed by their LD
50
values: PR8, 32 plaque-forming units (PFU); HA
Min
, 1.7 × 10
3
PFU; NA
Min
, 2.4 × 10
5
PFU; (NA+HA)
Min
, ≥3.16 × 10
6
PFU. Remarkably, (NA+HA)
Min
was attenuated >100,000-fold, with NA
Min
the major contributor to attenuation. In vaccinated mice (NA+HA)
Min
was highly effective in providing long-lasting protective immunity against lethal WT challenge at a median protective dose (PD
50
) of 2.4 PFU. Moreover, at a PD
50
of only 147 or 237, (NA+HA)
Min
conferred protection against heterologous lethal challenges with two mouse-adapted H3N2 viruses. We conclude that the suppression of HA and NA is a unique strategy in live vaccine development.
Formulae and performativity in Middle English documents
Authors: Rütten Tanja
Published: May 2013

This paper investigates the performative nature of Late Middle English administrative documents. While certain documents indicate the instantaneous performance of a speech act by using the canonical construction “I (hereby) + speech act verb”, explicit performatives are frequently inscribed with third-person reference of different kinds. This suggests that performativity may be a gradable phenomenon and that certain pragmatic contexts generate performative constructions which serve to (re)activate the speech act at some other point in time. In a quantitative study based on the Middle English Grammar Corpus, this paper provides a survey of the distributional patterns of three conceptionally distinct types of explicit performative constructions in documents. While the canonical construction seems to be tied to oral communication, related forms with third-person reference give documents a more autonomous status. Detaching the written record from the oral ceremony, these constructions facilitate a later verbatim reactivation of the respective speech act.
Universal Minimal Structure
Authors: Vainikka Anne , Young-Scholten Martha
Published: May 2013

This paper addresses the fundamental question of whether (or how) functional projections are acquired during the development of syntax. However, rather than concentrating on the actual acquisition of functional projections, we consider the starting point of syntactic development: if functional projections develop during acquisition, there must be an early stage that can at least occasionally be attested that does not reveal evidence of functional projections. The relevant data concerns utterances distinct from the target language that appear to involve reduced structure. By briefly reviewing the relevant literature, we conclude that there is suggestive evidence that reduced structure is an option for all language learners. This points to the conclusion that the possibility of positing reduced structure is an option in the language module, regardless of age.
Indeterminacy in grammar and acquisition
Authors: Katis Demetra , Nikiforidou Kiki
Published: May 2013

The formalist definition of relative clauses as a clearly distinct construction with two syntactically linked clauses has been recently questioned by cross-linguistic evidence. It is here further undermined by a discussion of constructions in Modern Greek, which although deviating from the structural definition conform nonetheless to a semantic-pragmatic one. Above all, acquisition data is presented as independent support for a unified approach to relatives, which can be based on conceptual integration. Syntactically underspecified relatives are shown to appear as early as syntactically-driven ones, with those based on more transparent semantic linking of clauses preceding those based on pragmatic linking. This suggests early handling of the metonymic nature of grammar but also a growing cognitive ability for more indeterminate grammatical relationships.