bluuebunny/crossref_metadata_2025 huggingface dataset:
Vortex ring formation in starting forced plumes with negative and positive buoyancy
Authors: Gao L. , Yu S. C. M.
Published: November 2016

The limiting process of vortex ring formation in starting forced plumes, with Richardson number in the range of −0.06 ≤ Ri ≤ 0.06, was studied numerically under the Boussinesq approximation. The examination of the dynamics of the starting flow evolution reveals that the plume-ambient density difference affects the vortex ring pinch-off mainly through three mechanisms, i.e., the baroclinic production of vorticity, the buoyancy acceleration (or deceleration) on the vortical structures, and its effect on the trailing shear layer instability. As Ri increases from negative to positive values, three regimes can be identified in terms of the vortex interaction patterns during the pinch-off process, i.e., the weak-interaction regime (−0.06 < Ri < − 0.02), the transition regime (−0.02 ≤ Ri < 0), and the strong-interaction regime (0 ≤ Ri < 0.06). By eliminating the influence of the baroclinic vorticity production, the circulation method proposed for the starting jets is revised to determine the buoyant formation number F in the starting forced plumes. Besides the formation number F, another dimensionless time scale (dubbed as the separation number S), which corresponds to the end of the pinch-off process, is identified by the time of vanishment of the vorticity flux feeding the leading vortex ring. The numerical results show that the variation trends of formation number and separation number against Ri change near the critical value of Ric ≈ − 0.02. In the weak-interaction regime, both formation number and separation number increase rapidly against Ri. While in the transition and strong-interaction regimes alike, the formation number increases at a much slower rate than in the weak-interaction regime, and the separation number declines dramatically as Ri increases. Finally, a qualitative explanation on the variation patterns of formation number and separation number is proposed based on the buoyancy effects on the dynamic properties of the leading vortex ring and the vortex interaction patterns.
The impact of nitrogen content and vacancies on structure and mechanical properties of Mo–N thin films
Authors: Klimashin F. F. , Koutná N. , Euchner H. , Holec D. , Mayrhofer P. H.
Published: November 2016

Based on a combined computational and experimental study, we show that besides the thermodynamically stable β-MoN0.5 and δ2-MoN phases, also metastable γ-MoNx and its ordered relative γ′-MoNx can be synthesized by physical vapor deposition. The formation of the NaCl-based γ-MoNx phase is favored for nitrogen concentrations between 23 and 34 at.% (i.e., x = 0.30–0.53). Higher nitrogen contents (close to the 3:2 stoichiometry, hence, MoN0.67) favor the ordering of the vacancies at the nitrogen sublattice (hence, γ′-MoNx). The highest hardness of ∼33 GPa is obtained for single-phase cubic-structured γ-MoN0.53 coatings, whereas the ordered γ′-MoN0.67 coatings are slightly softer with a hardness of ∼28 GPa.
Analysis of magnetically immersed electron guns with non-adiabatic fields
Authors: Pikin Alexander , Alessi James G. , Beebe Edward N. , Raparia Deepak , Ritter John
Published: November 2016

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams with high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map, different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. The tests’ results of a non-adiabatic electron gun with modified magnetic field are presented.
Calibrating ion density profile measurements in ion thruster beam plasma
Authors: Zhang Zun , Tang Haibin , Ren Junxue , Zhang Zhe , Wang Joseph
Published: November 2016

The ion thruster beam plasma is characterized by high directed ion velocity (104 m/s) and low plasma density (1015 m−3). Interpretation of measurements of such a plasma based on classical Langmuir probe theory can yield a large experimental error. This paper presents an indirect method to calibrate ion density determination in an ion thruster beam plasma using a Faraday probe, a retarding potential analyzer, and a Langmuir probe. This new method is applied to determine the plasma emitted from a 20-cm-diameter Kaufman ion thruster. The results show that the ion density calibrated by the new method can be as much as 40% less than that without any ion current density and ion velocity calibration.
Vibrationally resolved UV/Vis spectroscopy with time-dependent density functional based tight binding
Authors: Rüger Robert , Niehaus Thomas , van Lenthe Erik , Heine Thomas , Visscher Lucas
Published: November 2016

We report a time-dependent density functional based tight-binding (TD-DFTB) scheme for the calculation of UV/Vis spectra, explicitly taking into account the excitation of nuclear vibrations via the adiabatic Hessian Franck-Condon method with a harmonic approximation for the nuclear wavefunction. The theory of vibrationally resolved UV/Vis spectroscopy is first summarized from the viewpoint of TD-DFTB. The method is benchmarked against time-dependent density functional theory (TD-DFT) calculations for strongly dipole allowed excitations in various aromatic and polar molecules. Using the recent 3ob:freq parameter set of Elstner’s group, very good agreement with TD-DFT calculations using local functionals was achieved.
Oscillator versus prefundamental representations
Authors: Boos Hermann , Göhmann Frank , Klümper Andreas , Nirov Khazret S. , Razumov Alexander V.
Published: November 2016

We find the ℓ-weights and the corresponding ℓ-weight vectors for the finite and infinite dimensional representations of the quantum loop algebras Uq(ℒ(𝔰𝔩2)) and Uq(ℒ(𝔰𝔩3)) obtained from the Verma representations of the quantum groups Uq(𝔤𝔩2) and Uq(𝔤𝔩3) via the Jimbo’s homomorphism. Then we find the ℓ-weights and the ℓ-weight vectors for the q-oscillator representations of the positive Borel subalgebras of the same quantum loop algebras. This allows, in particular, to relate the q-oscillator and prefundamental representations.
The best of both Reps—Diabatized Gaussians on adiabatic surfaces
Authors: Meek Garrett A. , Levine Benjamin G.
Published: November 2016

When simulating nonadiabatic molecular dynamics, choosing an electronic representation requires consideration of well-known trade-offs. The uniqueness and spatially local couplings of the adiabatic representation come at the expense of an electronic wave function that changes discontinuously with nuclear motion and associated singularities in the nonadiabatic coupling matrix elements. The quasi-diabatic representation offers a smoothly varying wave function and finite couplings, but identification of a globally well-behaved quasi-diabatic representation is a system-specific challenge. In this work, we introduce the diabatized Gaussians on adiabatic surfaces (DGAS) approximation, a variant of the ab initio multiple spawning (AIMS) method that preserves the advantages of both electronic representations while avoiding their respective pitfalls. The DGAS wave function is expanded in a basis of vibronic functions that are continuous in both electronic and nuclear coordinates, but potentially discontinuous in time. Because the time-dependent Schrödinger equation contains only first-order derivatives with respect to time, singularities in the second-derivative nonadiabatic coupling terms (i.e., diagonal Born-Oppenheimer correction; DBOC) at conical intersections are rigorously absent, though singular time-derivative couplings remain. Interpolation of the electronic wave function allows the accurate prediction of population transfer probabilities even in the presence of the remaining singularities. We compare DGAS calculations of the dynamics of photoexcited ethene to AIMS calculations performed in the adiabatic representation, including the DBOC. The 28 fs excited state lifetime observed in DGAS simulations is considerably shorter than the 50 fs lifetime observed in the adiabatic simulations. The slower decay in the adiabatic representation is attributable to the large, repulsive DBOC in the neighborhood of conical intersections. These repulsive DBOC terms are artifacts of the discontinuities in the individual adiabatic vibronic basis functions and therefore cannot reflect the behavior of the exact molecular wave function, which must be continuous.
Cryogenic setup for trapped ion quantum computing
Authors: Brandl M. F. , van Mourik M. W. , Postler L. , Nolf A. , Lakhmanskiy K. , Paiva R. R. , Möller S. , Daniilidis N. , Häffner H. , Kaushal V. , Ruster T. , Warschburger C. , Kaufmann H. , Poschinger U. G. , Schmidt-Kaler F. , Schindler P. , Monz T. , Blatt R.
Published: November 2016

We report on the design of a cryogenic setup for trapped ion quantum computing containing a segmented surface electrode trap. The heat shield of our cryostat is designed to attenuate alternating magnetic field noise, resulting in 120 dB reduction of 50 Hz noise along the magnetic field axis. We combine this efficient magnetic shielding with high optical access required for single ion addressing as well as for efficient state detection by placing two lenses each with numerical aperture 0.23 inside the inner heat shield. The cryostat design incorporates vibration isolation to avoid decoherence of optical qubits due to the motion of the cryostat. We measure vibrations of the cryostat of less than ±20 nm over 2 s. In addition to the cryogenic apparatus, we describe the setup required for an operation with 40Ca+ and 88Sr+ ions. The instability of the laser manipulating the optical qubits in 40Ca+ is characterized by yielding a minimum of its Allan deviation of 2.4 ⋅ 10−15 at 0.33 s. To evaluate the performance of the apparatus, we trapped 40Ca+ ions, obtaining a heating rate of 2.14(16) phonons/s and a Gaussian decay of the Ramsey contrast with a 1/e-time of 18.2(8) ms.
Flows induced by exponential stretching and shearing plate motions
Authors: Weidman Patrick
Published: November 2016

Boundary-layer solutions for the flow induced by an exponentially stretching surface also sheared in its own plane are given. Prior to this study no similarity solutions have been reported for flows generated by exponentially sheared surfaces concomitant with surface stretching in any form. The method of solution is self-similarity. The results found here are intimately related to those of Magyari and Keller [“Heat and mass transfer in the boundary layers on an exponentially stretching continuous surface,” J. Phys. D: Appl. Phys. 32, 577–585 (1999)] who studied the motion and heat transfer induced by an exponentially stretching plate. In addition to two particular cases reported here, a third situation is found where an exponentially stretching surface admits a concomitant arbitrary streamwise shearing motion.
A total station spatial positioning method based on rotary laser scanning and ultrasonic ranging
Authors: Wu Jun , Zhu Jigui , Yu Zhijing , Zhuge Jingchang , Xue Bin
Published: November 2016

Total station spatial coordinator measuring technology is extensively applied in the large-scale measurement of industrial assembly and manufacturing for its flexibility and adaptability. The existing total station technology has some principal limits such as poor efficiency and single tasking; in order to achieve the total station spatial coordinator measuring technology with the advantages of multi-task, real-time measurement, and high accuracy, this paper presents a novel total station measurement method by using multi-laser plane constraints established through rotating planar planes and distance information obtained with an ultrasonic ranging method. With the spatial divergence angles of the optoelectronic scanning and ultrasonic arrays, this method can measure the spatial coordinates in multi-task and real-time with a single station and a portable target bar. Experimental results show that the proposed method is feasible and valid with satisfactory accuracy. The maximum distance measurement error is less than 0.2 mm in a volume that is 5 m far away from the station.
The eddy current probe array for Keda Torus eXperiment
Authors: Li Zichao , Li Hong , Tu Cui , Hu Jintong , You Wei , Luo Bing , Tan Mingsheng , Adil Yolbarsop , Wu Yanqi , Shen Biao , Xiao Bingjia , Zhang Ping , Mao Wenzhe , Wang Hai , Wen Xiaohui , Zhou Haiyang , Xie Jinlin , Lan Tao , Liu Adi , Ding Weixing , Xiao Chijin , Liu Wandong
Published: November 2016

In a reversed field pinch device, the conductive shell is placed as close as possible to the plasma so as to balance the plasma during discharge. Plasma instabilities such as the resistive wall mode and certain tearing modes, which restrain the plasma high parameter operation, respond closely with conditions in the wall, in essence the eddy current present. Also, the effect of eddy currents induced by the external coils cannot be ignored when active control is applied to control instabilities. One diagnostic tool, an eddy current probe array, detects the eddy current in the composite shell. Magnetic probes measuring differences between the inner and outer magnetic fields enable estimates of the amplitude and angle of these eddy currents. Along with measurements of currents through the copper bolts connecting the poloidal shield copper shells, we can obtain the eddy currents over the entire shell. Magnetic field and eddy current resolutions approach 2 G and 6 A, respectively. Additionally, the vortex electric field can be obtained by eddy current probes. As the conductivity of the composite shell is high, the eddy current probe array is very sensitive to the electric field and has a resolution of 0.2 mV/cm. In a bench test experiment using a 1/4 vacuum vessel, measurements of the induced eddy currents are compared with simulation results based on a 3D electromagnetic model. The preliminary data of the eddy currents have been detected during discharges in a Keda Torus eXperiment device. The typical value of toroidal and poloidal eddy currents across the magnetic probe coverage rectangular area could reach 3.0 kA and 1.3 kA, respectively.
Growth of continuous graphene by open roll-to-roll chemical vapor deposition
Authors: Zhong Guofang , Wu Xingyi , D'Arsie Lorenzo , Teo Kenneth B. K. , Rupesinghe Nalin L. , Jouvray Alex , Robertson John
Published: November 2016

We demonstrate the growth of high-quality, continuous monolayer graphene on Cu foils using an open roll-to-roll (R2R) chemical vapor deposition (CVD) reactor with both static and moving foil growth conditions. N2 instead of Ar was used as carrier gas to reduce process cost, and the concentrations of H2 and CH4 reactants were kept below the lower explosive limit to ensure process safety for reactor ends open to ambient. The carrier mobility of graphene deposited at a Cu foil winding speed of 5 mm/min was 5270–6040 cm2 V−1 s−1 at room temperature (on 50 μm × 50 μm Hall devices). These results will enable the inline integration of graphene CVD for industrial R2R production.
Ultra-high vacuum compatible preparation chain for intermetallic compounds
Authors: Bauer A. , Benka G. , Regnat A. , Franz C. , Pfleiderer C.
Published: November 2016

We report the development of a versatile material preparation chain for intermetallic compounds, which focuses on the realization of a high-purity growth environment. The preparation chain comprises an argon glovebox, an inductively heated horizontal cold boat furnace, an arc melting furnace, an inductively heated rod casting furnace, an optically heated floating-zone furnace, a resistively heated annealing furnace, and an inductively heated annealing furnace. The cold boat furnace and the arc melting furnace may be loaded from the glovebox by means of a load-lock permitting to synthesize compounds starting with air-sensitive elements while handling the constituents exclusively in an inert gas atmosphere. All furnaces are all-metal sealed, bakeable, and may be pumped to ultra-high vacuum. We find that the latter represents an important prerequisite for handling compounds with high vapor pressure under high-purity argon atmosphere. We illustrate the operational aspects of the preparation chain in terms of the single-crystal growth of the heavy-fermion compound CeNi2Ge2.
Electronic properties of monolayer tungsten disulfide grown by chemical vapor deposition
Authors: Alharbi Abdullah , Shahrjerdi Davood
Published: November 2016

We demonstrate chemical vapor deposition of large monolayer tungsten disulfide (WS2) (>200 μm). Photoluminescence and Raman spectroscopy provide insight into the structural and strain heterogeneity of the flakes. We observe exciton quenching at grain boundaries that originate from the nucleation site at the center of the WS2 flakes. Temperature variable transport measurements of top-gated WS2 transistors show an apparent metal-to-insulator transition. Variable range and thermally activated hopping mechanisms can explain the carrier transport in the insulating phase at low and intermediate temperatures. The devices exhibit room-temperature field-effect electron mobility as high as 48 cm2/V.s. The mobility increases with decreasing temperature and begins to saturate at below 100 °K, possibly due to Coulomb scattering or defects.
Modifications of plasma density profile and thrust by neutral injection in a helicon plasma thruster
Authors: Takahashi Kazunori , Takao Yoshinori , Ando Akira
Published: November 2016

Argon propellant is introduced from the upstream and downstream sides of a high power helicon plasma thruster. The plasma density profile and the imparted thrust are measured for various upstream and downstream argon flow rates, where the total gas flow rate of 70 sccm and the resultant vacuum chamber pressure of 0.2 mTorr are maintained. It is observed that the imparted thrust increases with an increase in the downstream gas flow rate; simultaneously an upstream-peaking profile of the plasma density observed for the upstream gas injection becomes uniform for the downstream gas injection. The difference in the thrust between the upstream and downstream gas injections is enhanced by increasing the rf power. The observed density profiles are qualitatively consistent with theoretical predictions taking a neutral depletion effect into account.
The relativistic electro-vortical field—revisiting magneto-genesis and allied problems
Authors: Mahajan Swadesh M.
Published: November 2016

Following the idea of MagnetoFluid unification [S. M. Mahajan, Phys. Rev. Lett. 90, 035001 (2003)], a very general Electro-Vortical (EV) field is constructed to describe the dynamics of a perfect relativistic fluid. Structurally similar to the electromagnetic field Fμν, the Electro-Vortical field Mνμ unifies the macroscopic forces into a single grand force that is the weighted sum of the electromagnetic and the inertial/thermal forces. The new effective force may be viewed either as a vortico-thermal generalization of the electromagnetic force or as the electromagnetic generalization of the vortico-thermal forces that a fluid element experiences in course of its evolution. Two fundamental consequences follow from this grand unification: (1) emergences of a new helicity that is conserved for arbitrary thermodynamics and (2) the entire dynamics is formally expressible as an MHD (magnetohydrodynamics) like ideal Ohm's law in which the “electric” and “magnetic” components of the EV field replace the standard electric and magnetic fields. In the light of these more and more encompassing conserved helicities, the “scope and significance” of the classical problem of magneto-genesis (need for a seed field to get a dynamo started) is reexamined. It is shown that in models more advanced than MHD, looking for exotic seed-generation mechanisms (like the baroclinic thermodynamics) should not constitute a fundamental pursuit; the totally ideal dynamics is perfectly capable of generating and sustaining magnetic fields entirely within its own devices. For a specified thermodynamics, a variety of exact and semi exact self-consistent analytical solutions for equilibrium magnetic and flow fields are derived for a single species charged fluid. The scale lengths of the fields are determined by two natural scale lengths: the skin depth and the gradient length of the thermodynamic quantities. Generally, the skin depth, being the shorter (even much shorter) than the gradient length, will characterize the kinetic-magnetic reservoir of short scale energy that will drive the dynamo as well as reverse dynamo action—the creation of large scale magnetic and flow fields.
The structures of magnetic islands formed during collisionless magnetic reconnections in a force-free current sheet
Authors: Fan Feibin , Huang Can , Lu Quanming , Xie Jinlin , Wang Shui
Published: November 2016

In this paper, with a two-dimensional particle-in-cell simulation model, we compare the structures of a primary magnetic island to those of a secondary magnetic island, and these islands are formed during collisionless magnetic reconnection in a force-free current sheet. The out-of-plane magnetic field By is enhanced in the center of both the primary and secondary islands; however, a quadrupole structure of By with a good symmetry may be formed at the ends of the primary island. The in-plane electric field also exists in both the primary and secondary islands. The electric field Ex has a positive value in the left and a negative value in the right of the islands, while the electric field Ez has a positive value in the upper part and a positive value in the lower part of the islands. However, the in-plane electric field exists in the outer part of the primary island, while it exists in the center of the secondary island.
Characteristics of capacitively coupled RF helium/neon discharges in a hollow fiber
Authors: Duan Lian , Wang Xinbing , Zuo Duluo
Published: November 2016

Capacitively coupled radio-frequency microplasmas are produced in hollow fibers with an inner diameter of hundreds of micrometers powered by an 80-MHz power supply. Considering the narrow space of the hollow core, optical emission spectrometry is used to obtain the spatially resolved characteristics of the microplasmas. The rotational temperature, excitation temperature, and electron density of microplasmas are determined based on the second positive band of nitrogen, the atomic spectra of bulk neutral particles of plasmas, and the Hβ line of the hydrogen Balmer series, respectively. In our experiments, the rotational temperature, excitation temperature, and electron density of typical inert gases helium and neon are in the ranges of 300–500 K, 7000–9500 K, and 1013 cm−3, respectively. The results obtained with different external parameters of power and pressure show that the light emission intensity increases with power and pressure. The distributions of the rotational temperature, excitation temperature, and electron density of the microplasmas are almost constant over the gap between the electrodes. These distributions are mostly insensitive to the change of power and pressure in single-component plasmas. The characteristics of mixed plasmas are also investigated. The plasma with a larger helium content possesses higher excitation temperature and lower rotational temperature and electron density than those of the plasma with a lower helium content.
Optical control of plasmonic heating effects using reversible photo-alignment of nematic liquid crystals
Authors: Palermo Giovanna , Cataldi Ugo , De Sio Luciano , Bürgi Thomas , Tabiryan Nelson , Umeton Cesare
Published: November 2016

We demonstrate and characterize an optical control of the plasmonic heat delivered by a monolayer substrate of gold nanoparticles, obtained by modulating the effective refractive index of the neighboring dielectric medium. The effect, which exploits the dependence of the nematic liquid crystal (NLC) refractive index on the molecular director orientation, is realized by using a polarization dependent, light-induced molecular reorientation of a thin film of photo-alignment layer that the NLC is in contact with. For a suitable alignment, plasmonic pumping intensity values ranging from 0.25 W/cm2 to 6.30 W/cm2 can induce up to 17.4 °C temperature variations in time intervals of the order of seconds. The reversibility of the optically induced NLC molecular director orientation enables an active control of the plasmonic photo-induced heat.
Imaging and manipulation of skyrmion lattice domains in Cu2OSeO3
Authors: Zhang S. L. , Bauer A. , Berger H. , Pfleiderer C. , van der Laan G. , Hesjedal T.
Published: November 2016

Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising binary state variables in high-density, low-energy nonvolatile memory. Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which makes it difficult to write information unless they are spatially broken up into smaller units, each representing a bit. Thus, the formation and manipulation of skyrmion lattice domains is a prerequisite for memory applications. Here, using an imaging technique based on resonant magnetic x-ray diffraction, we demonstrate the mapping and manipulation of skyrmion lattice domains in Cu2OSeO3. The material is particularly interesting for applications owing to its insulating nature, allowing for electric field-driven domain manipulation.
Nonlinear propagation of stress waves during high speed cutting
Authors: Jiang Yifei , Zhang Jun , He Yong , Liu Hongguang , Zhao Wanhua
Published: November 2016

Stress waves induced by high speed cutting (HSC) were demonstrated visually, and the dependence of their nonlinear propagation characteristics on cutting speed was studied. The time-resolved photoelasticity imaging technique in the bright-field mode was used to observe stress waves in the workpiece, and the obtained photoelastic images were evaluated semi-quantitatively. The experimental results were quantitatively reproduced via the lattice model, which helped explain our observations by analyzing the superposition of stress waves. According to the further simulation, we find that as the cutting speed increases, the stress intensity of the workpiece near the cutting tool is not in a linear enhancement process, with strong distortion of stress field under the superposition of different stress wave components. These help us have a deep understanding about the HSC mechanism under stress waves' effects.
Probing the exciton-phonon coupling strengths of O-polar and Zn-polar ZnO wafer using hard X-ray excited optical luminescence
Authors: Lin Bi-Hsuan , Chen Huang-Yeh , Tseng Shao-Chin , Wu Jian-Xing , Chen Bo-Yi , Lee Chien-Yu , Yin Gung-Chian , Chang Shih-Hung , Tang Mau-Tsu , Hsieh Wen-Feng
Published: November 2016

The temperature-dependent hard X-ray excited optical luminescence (XEOL) spectroscopy was used to study the optical properties of O and Zn polarity of a c-plane single crystal ZnO wafer. By analyzing the XEOL and XRD, we found an unprecedented blue shift of the free exciton transition with increasing the excited carrier density as tuning the X-ray energy across the Zn K-edge, and the O-polar face possesses better crystal structure than the Zn-polar one. This spectral blue shift is attributed to the Coulomb screening of the spontaneous polarization by the excited free carriers that result in decreasing the exciton-phonon Fröhlich interaction to reduce exciton binding energy.
Ring-Opening Dispersion Polymerization of ʟ-Lactide with Polylactide Stabilizer in Supercritical Carbon Dioxide
Authors: Deng Jinjun , Zhan Shiping , Wang Jingchang , Liu Zhijun , Li Zhiyi
Published: November 2016

Non-fluorous triblock copolymers of poly(l-lactide)-block-hydroxypropyl-terminated poly(dimethyl siloxanes)-block-poly(l-lactide) (PLLA-HTPDMS-PLLA) with two different molecular weights in the range of 4800 to 6500 Da, were prepared by changing the ratio of HTPDMS to l-lactide (L-LA), and were used as stabilizers for the ring-opening dispersion polymerization (RODP) of L-LA to prepare poly(l-lactide) (PLLA) in supercritical carbon dioxide (ScCO2). The experimental results showed that the prepared non-fluorous triblock copolymers were very effective as new stabilizers for the RODP and fine powders of PLLA were obtained. The structure of the stabilizers and PLLA were characterized by 1H NMR and FTIR spectroscopy. The morphology of PLLA was investigated by scanning electron microscopy (SEM). The effects of the CO2-philic/lipophilic segment lengths of the stabilizers on the RODP were explored. The effects of the stabilizer concentration on the polymerization yield, molecular weight, and morphology of PLLA were investigated.
Coastal sea level rise with warming above 2 °C
Authors: Jevrejeva Svetlana , Jackson Luke P. , Riva Riccardo E. M. , Grinsted Aslak , Moore John C.
Published: November 2016

Significance

Warming of 2 °C will lead to an average global ocean rise of 20 cm, but more than 90% of coastal areas will experience greater rises. If warming continues above 2 °C, then, by 2100, sea level will be rising faster than at any time during human civilization, and 80% of the global coastline is expected to exceed the 95th percentile upper limit of 1.8 m for mean global ocean sea level rise. Coastal communities, notably rapidly expanding cities in the developing world; small island states; United Nations Educational, Scientific and Cultural Organization Cultural World Heritage sites; and vulnerable tropical coastal ecosystems will have a very limited time after midcentury to adapt to these rises.
Temporal coding of reward-guided choice in the posterior parietal cortex
Authors: Hawellek David J. , Wong Yan T. , Pesaran Bijan
Published: November 2016

Significance

A central question in systems neuroscience is how cognitive functions can arise from the interplay of many different brain areas. For example the cognitive act of forming a decision requires a concerted computation involving sensory, mnemonic, and executive information residing in neural circuits that have different anatomical locations, that operate on different temporal scales, and that extend over different spatial dimensions. We find that in a central cortical hub—the posterior parietal cortex—firing rate information about upcoming decisions is pulsed according to intrinsic temporal structure in the beta- and gamma-frequency ranges. The brain may use temporal structure at several time scales to support distributed computations that underlie reward-guided decisions.
Quasimodo mediates daily and acute light effects on
Drosophila
clock neuron excitability
Authors: Buhl Edgar , Bradlaugh Adam , Ogueta Maite , Chen Ko-Fan , Stanewsky Ralf , Hodge James J. L.
Published: November 2016

Significance

Most organisms developed a circadian clock to adapt their behavior to daily changes of light and temperature. The molecular clock is remarkably conserved across species with much of our current understanding coming from
Drosophila
studies. To generate circadian behavior, appropriate levels of neuronal electrical activity are crucial, but the regulators of this activity have remained largely elusive. Here we identify three membrane proteins that interact to set the clock neurons to “day” or “night,” forming a light-input pathway to the circadian clock. The membrane-anchored extracellular protein Quasimodo affects both the daily changes in physiological properties and light responses of brain clock neurons, possibly acting upstream of the potassium channel Shaw and the Na
+
, K
+
, Cl
−
ion transporter NKCC.
For blacks in America, the gap in neighborhood poverty has declined faster than segregation
Authors: Firebaugh Glenn , Acciai Francesco
Published: November 2016

Significance

Racial inequality in America persists in part because of racial differences in exposure to adverse neighborhood environments. Blacks in particular are significantly more likely than other Americans to live in high-poverty neighborhoods—neighborhoods characterized by poor schools and limited access to healthcare, jobs, and beneficial social networks—resulting in inequality of opportunity, as life chances are diminished for residents of such neighborhoods. In addition, the greater exposure to crime, noise, and congestion implies a lower quality of life, on average, for black Americans. Because black neighborhood disadvantage results in inequality of life chances based on race, it is important to determine the direction, pace, and sources of change in black–nonblack differences in neighborhood poverty in America.
Gut microbiota induce IGF-1 and promote bone formation and growth
Authors: Yan Jing , Herzog Jeremy W. , Tsang Kelly , Brennan Caitlin A. , Bower Maureen A. , Garrett Wendy S. , Sartor Balfour R. , Aliprantis Antonios O. , Charles Julia F.
Published: November 2016

Significance

New interventions are needed to improve bone health and reduce the risk for osteoporosis and fracture. Dysbiosis is increasingly linked to metabolic abnormalities, although the effect of the microbiota on skeletal health is poorly understood. Previous studies suggest microbiota are detrimental to bone by increasing resorption. In this report, we show that the gut resident microbiota promote bone formation, as well as resorption, with long-term exposure to microbiota resulting in net skeletal growth. Microbiota induce the hormone insulin-like growth factor 1 (IGF-1), which promotes bone growth and remodeling. Short-chain fatty acids (SCFAs), produced when microbiota ferment fiber, also induce IGF-1, suggesting a mechanism by which microbiota affect bone health. Manipulating the microbiome or its metabolites may afford opportunities to optimize bone health and growth.
Mapping human temporal and parietal neuronal population activity and functional coupling during mathematical cognition
Authors: Daitch Amy L. , Foster Brett L. , Schrouff Jessica , Rangarajan Vinitha , Kaşikçi Itır , Gattas Sandra , Parvizi Josef
Published: November 2016

Significance

Humans have the unique ability to perform exact mental arithmetic, which derives from the association of symbols (e.g., “3”) with discrete quantities. Using direct intracranial recordings, we measured electrophysiological activity from neuronal populations in the lateral parietal cortex (LPC) and ventral temporal cortex (VTC) that are known to be important for numerical processing as subjects performed various experiments. We observed functional heterogeneity within each region at the millimeter and millisecond scales and report empirical evidence of functional coupling between the LPC and VTC during mathematical cognition. Our results suggest the presence of an anatomically selective numerical cognition system that engages discrete neuronal populations of the ventral temporal and lateral parietal regions in different time windows of numerical processing.
Chemical and mechanical stimuli act on common signal transduction and cytoskeletal networks
Authors: Artemenko Yulia , Axiotakis Lucas , Borleis Jane , Iglesias Pablo A. , Devreotes Peter N.
Published: November 2016

Significance

Cells directionally migrate in response to a variety of external cues, including chemical, electrical, and mechanical stimuli; however, only response to chemoattractants has been characterized at the molecular level. Binding of chemoattractants to specific surface receptors triggers rapid, transient activation of many signal transduction and cytoskeletal events. We discovered that brief application of shear stress to cells likely elicits activation of all of the same events. Responses to chemoattractants and shear stress are susceptible to many of the same perturbations, although that to mechanical stimulation uniquely is blocked by disruption of the actin cytoskeleton. Our finding provides insight into the molecular mechanism of cellular response to mechanical stimuli and has important implications for integration of chemical and mechanical inputs.
Illuminating a plant’s tissue-specific metabolic diversity using computational metabolomics and information theory
Authors: Li Dapeng , Heiling Sven , Baldwin Ian T. , Gaquerel Emmanuel
Published: November 2016

Significance

Population geneticists have educated molecular biologists in how to harness the statistical power of variance arising from interindividual natural variation to elucidate gene function in plants. The metabolic differences among tissues within a plant provide another source of variance that can be harnessed in the quest to understand gene function. We combine the power of information theory statistics and computational metabolomics to parse metabolic diversity within an ecological model plant,
Nicotiana attenuata
, to reveal intriguing patterns of metabolic specialization in floral limb and anthers, the responsible mechanisms of which we parse further by detecting and silencing the expression of two UDP-glycosyltransferases involved in floral flavonoid metabolism. The workflow defines a framework for future evolutionary studies on plant tissue metabolic specialization.
Quantitative determination of ribosome nascent chain stability
Authors: Samelson Avi J. , Jensen Madeleine K. , Soto Randy A. , Cate Jamie H. D. , Marqusee Susan
Published: November 2016

Significance

A fundamental question in biology is how the biophysical parameters describing protein folding in vitro are altered during cotranslational folding. Because protein synthesis is slow, nascent chains can fold cotranslationally while still tethered to the ribosome and before the entire protein has emerged. Here we examine the effects of ribosomal tethering on protein stability and how that stability is modulated by the distance away from the ribosome’s active site. We develop a quantitative assay for measuring protein stability on stalled nascent chains and find that the ribosome destabilizes nascent chains. This destabilization may play a key role in ensuring folding fidelity by helping the nascent chain avoid partially folded kinetic traps before the entire chain has been synthesized.
The cholinergic forebrain arousal system acts directly on the circadian pacemaker
Authors: Yamakawa Glenn R. , Basu Priyoneel , Cortese Filomeno , MacDonnell Johanna , Whalley Danica , Smith Victoria M. , Antle Michael C.
Published: November 2016

Significance

Sleep and wake states are regulated by a variety of mechanisms. One such important system is the circadian clock, which provides temporal structure to sleep and wake. Conversely, changes in behavioral state can influence the phase of the circadian clock. Here we demonstrate that the level of wakefulness is critical for arousal to reset circadian clock phase. We then show that treatments that produce arousal and reset the circadian clock activate the basal forebrain. Finally, we demonstrate that cholinergic input from the basal forebrain is both necessary and sufficient for eliciting this arousal-induced resetting of the circadian clock. These results establish a functional link between the major forebrain arousal center and the circadian system.
Spatiotemporal dynamics of androgen signaling underlie sexual differentiation and congenital malformations of the urethra and vagina
Authors: Larkins Christine E. , Enriquez Ana B. , Cohn Martin J.
Published: November 2016

Significance

Disorders of sex development (DSDs) and some non-DSD human syndromes result in female genitourinary malformations. The mechanisms of genitourinary development are beginning to be understood in males; however, little is known about female lower genitourinary organogenesis. Prenatal exposure to excessive endogenous or exogenous androgens can disrupt sexual differentiation of the female urethra and vagina, but the mechanisms responsible for these malformations are not well understood. This study sheds new light on development of vaginal anomalies in DSDs by (
i
) identifying the critical period of female development when vaginal position and feminization of the urethra is established and (
ii
) showing that this process is controlled by an androgen-responsive subpopulation of mesenchymal cells adjacent to the urogenital sinus.
Engineering dynamical control of cell fate switching using synthetic phospho-regulons
Authors: Gordley Russell M. , Williams Reid E. , Bashor Caleb J. , Toettcher Jared E. , Yan Shude , Lim Wendell A.
Published: November 2016

Significance

Many long-term cellular decisions in development, synaptic plasticity, and immunity require cells to recognize input dynamics such as pulse duration or frequency. In dynamically controlled cells, incoming stimuli are often processed and filtered by a rapid-acting signaling layer, and then passed to a downstream slow-acting layer that locks in a longer-term cellular response. Directly testing how such dual-timescale networks control dynamical regulation has been challenging because most tools in synthetic biology allow rewiring of slow gene expression circuits, but not of rapid signaling circuits. In this work, we developed modular peptide tags for engineering synthetic phosphorylation circuits. We used these phospho-regulons to build synthetic dual-timescale networks in which the dynamic responsiveness of a cell fate decision can be selectively tuned.
How social structures, space, and behaviors shape the spread of infectious diseases using chikungunya as a case study
Authors: Salje Henrik , Lessler Justin , Paul Kishor Kumar , Azman Andrew S. , Rahman M. Waliur , Rahman Mahmudur , Cummings Derek , Gurley Emily S. , Cauchemez Simon
Published: November 2016

Significance

Although the determinants of infectious disease transmission have been extensively investigated in small social structures such as households or schools, the impact of the wider environment (e.g., neighborhood) on transmission has received less attention. Here we use an outbreak of chikungunya as a case study where detailed epidemiological data were collected and combine it with statistical approaches to characterize the multiple factors that influence the risk of infectious disease transmission and may depend on characteristics of the individual (e.g., age, sex), of his or her close relatives (e.g., household members), or of the wider neighborhood. Our findings highlight the role that integrating statistical approaches with in-depth information on the at-risk population can have on understanding pathogen spread.
Abiotic methane formation during experimental serpentinization of olivine
Authors: McCollom Thomas M.
Published: November 2016

Significance

Abiotic methane discharged from serpentinizing rocks supplies metabolic energy to chemosynthetic microbial communities and may have done so since the earliest lifeforms evolved on Earth. Several recent reports have claimed observation of abiotic formation of methane during low-temperature serpentinization of olivine-rich rocks during laboratory experiments. However, using
13
C-labeled carbon sources, this study shows that the methane observed in such experiments is predominantly derived from background sources rather than abiotic synthesis. Conversely, more rapid production of methane is observed when an H
2
-rich vapor phase is present within the reaction vessel. Overall, the results indicate that in situ abiotic synthesis may contribute less methane to near-surface serpentinites than some recent studies have suggested.
X-ray and cryo-EM structures of monomeric and filamentous actin-like protein MamK reveal changes associated with polymerization
Authors: Löwe Jan , He Shaoda , Scheres Sjors H. W. , Savva Christos G.
Published: November 2016

Significance

Some bacteria contain tiny magnets, so-called magnetosomes, that allow them to swim oriented by the Earth’s magnetic field. An intracellular filamentous protein, MamK, has previously been shown to align the magnetosomes along a straight line to combine their magnetic moments. Here we show the structure the MamK filaments have at the atomic level. We also show what happens when individual MamK molecules come together to form the filaments, because it is known that filament formation triggers the hydrolysis of the ATP molecule bound to MamK. The structure of monomeric MamK was determined by X-ray crystallography and of the filament by electron cryomicroscopy, image processing, and helical reconstruction.
Design of a molecular support for cryo-EM structure determination
Authors: Martin Thomas G. , Bharat Tanmay A. M. , Joerger Andreas C. , Bai Xiao-chen , Praetorius Florian , Fersht Alan R. , Dietz Hendrik , Scheres Sjors H. W.
Published: November 2016

Significance

As the scope of macromolecular structure determination by cryo-electron microscopy (cryo-EM) is expanding rapidly, it is becoming increasingly clear that many biological complexes are too fragile to withstand the harsh conditions involved in making cryo-EM samples. We describe an original approach to protect proteins from harmful forces during cryo-EM sample preparation by enclosing them inside a three-dimensional support structure that we designed using DNA origami techniques. By binding the transcription cofactor p53 to a specific DNA sequence, and by modifying the position of this sequence in our support structure, we also sought to control the relative orientation of individual p53:DNA complexes.
Recent acceleration in coastal cliff retreat rates on the south coast of Great Britain
Authors: Hurst Martin D. , Rood Dylan H. , Ellis Michael A. , Anderson Robert S. , Dornbusch Uwe
Published: November 2016

Significance

Cliffed coasts erode when attacked by energetic waves. Cliff retreat threatens coastal assets and livelihoods. Understanding rates of past erosion is vital to quantifying these risks, particularly when confronted with expected increases in storminess and sea level, and given continued human occupation and engineering of coastal regions. Historical observations of cliff retreat span 150 y at most. We derived past cliff retreat rates over millennial time scales for chalk cliffs on the south coast of Great Britain by interpreting measured cosmogenic nuclides with numerical models. Our results provide evidence for accelerated erosion in recent centuries, which we suggest is driven by reduced sediment supply and thinning of beaches in the face of environmental and anthropogenic changes.
Regulation of embryonic neurogenesis by germinal zone vasculature
Authors: Tata Mathew , Wall Ivan , Joyce Andy , Vieira Joaquim M. , Kessaris Nicoletta , Ruhrberg Christiana
Published: November 2016

Significance

Neural progenitor cells (NPCs) proliferate to generate precursors for new neurons. To sustain this process, NPCs balance self-renewal with the generation of progeny committed to neuronal differentiation. In the adult mammalian brain, blood vessels and vessel-derived factors help regulate this balance by modulating NPC proliferation and quiescence, independently of vascular roles in providing oxygen and nutrients. In contrast, it has been proposed that vasculature regulates NPC behavior in the developing forebrain by alleviating tissue hypoxia. We show here that germinal zone vasculature in the embryonic hindbrain regulates the balance of NPC self-renewal with neuron production, independently of roles in tissue oxygenation. Information on how blood vessels regulate neurogenesis may aid in the design of therapies for brain regeneration in injury and disease.