bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of molecules in strong oscillating electric fields using time-dependent Hartree–Fock theory
Authors: Eshuis Henk , Balint-Kurti Gabriel G. , Manby Frederick R.
Published: March 2008

Restricted and unrestricted forms of time-dependent Hartree–Fock theory have been implemented and used to study the electronic dynamics of ethene, benzene, and the formaldehyde cation subjected to both weak and strong oscillating electric fields. Absorption spectra and frequency-dependent polarizabilities are calculated via the instantaneous dipole moment and its derivative. In the weak field limit the computed excitation energies agree very well with those obtained using linearized time-dependent Hartree–Fock theory, which is valid only in the low-field perturbation limit. For strong fields the spectra show higher-order excitations, and a shift in the position of the excitations, which is due to the nonadiabatic response of the molecules to the field. For open-shell systems in the presence of strong oscillating electric fields, unrestricted time-dependent Hartree–Fock theory predicts the value of Ŝ2 to vary strongly with time.
Linear optical response of current-carrying molecular junction: A nonequilibrium Green’s function–time-dependent density functional theory approach
Authors: Galperin Michael , Tretiak Sergei
Published: March 2008

We propose a scheme for calculation of linear optical response of current-carrying molecular junctions for the case when electronic tunneling through the junction is much faster than characteristic time of external laser field. We discuss relationships between nonequilibrium Green’s function (NEGF) and time-dependent density functional theory (TDDFT) approaches and derive expressions for optical response and linear polarizability within NEGF-TDDFT scheme. Corresponding results for isolated molecule, derived within TDDFT approach previously, are reproduced when coupling to contacts is neglected.
Topological photon
Authors: Tiwari S. C.
Published: March 2008

We associate intrinsic energy equal to hν∕2 with the spin angular momentum of photon, and propose a topological model based on orbifold in space and tifold in time as topological obstructions. The model is substantiated using vector wavefield disclinations. The physical photon is suggested to be a particlelike topological photon and a propagating wave such that the energy hν of photon is equally divided between spin energy and translational energy, corresponding to linear momentum of hν∕c. The enigma of wave-particle duality finds natural resolution, and the proposed model gives new insights into the phenomena of interference and emission of radiation.
Revealing the surface origin of green band emission from ZnO nanostructures by plasma immersion ion implantation induced quenching
Authors: Yang Y. , Sun X. W. , Tay B. K. , Cao Peter H. T. , Wang J. X. , Zhang X. H.
Published: March 2008

Surface defect passivation for ZnO nanocombs (NCBs), random nanowires (RNWs), and aligned nanowires (ANWs) was performed through a metal plasma immersion ion implantation with low bias voltages ranging from 0to10kV, where Ni was used as the modification ion. The depth of surface-originated green band (GB) emission is thus probed, revealing the surface origin of the GB. It is also found that the GB is closely related to oxygen gas content during growth of the nanostructures. The GB origin of NCBs and RNWs grown with higher oxygen content is shallower (∼0.5nm), which can be completely quenched with no bias applied. However, the GB origin of ANWs grown at lower oxygen content is much deeper (∼7nm) with a complete quenching bias of 10kV. Quenching of the GB can be attributed to passivation of the surface hole or electron trapping sites (oxygen vacancies) by Ni ions.
Electrohydrodynamic interaction induced by a dielectric barrier discharge
Authors: Borghi C. A. , Carraro M. R. , Cristofolini A. , Neretti G.
Published: March 2008

In the present work an experimental investigation on the electrohydrodynamic (EHD) interaction effect, induced by means of a dielectric barrier discharge on a 1atm subsonic air flow, is described. The air flow is obtained in an open circuit blowing wind tunnel at different air speeds. A plane plasma panel equipped with a dielectric discharge barrier system is immersed in the flow. A single phase sinusoidal power supply system, a superposition of a single phase sinusoidal system with a dc voltage supply, and a three phase symmetrical power supply configuration are considered. Electric, fluid dynamic, and spectroscopic diagnostic techniques are utilized. Pitot probe measurements are performed in the boundary layer on the plasma panel surface. Schlieren imaging is done to visualize the plasma sheath. Vibrational and rotational temperatures are evaluated by means of spectroscopic techniques. The force induced on the flow by the dielectric barrier discharge acts on the ions of the non-neutral sheath ahead of the plasma filament when travelling on the panel surface only. This causes a reduction of the time interval during which the force is active. The EHD effect and the momentum transfer to the gas flow in the boundary layer are reduced when the flow speed grows. An increase of the supply frequency and of the supply voltage causes an increase of the momentum transfer. In these experiments no significant increase of the efficiency of EHD effect is observed when utilizing the superposition of a dc voltage to a single phase power supply or a three phase power supply.
Nanoindentation studies of graded shape memory alloy thin films processed using diffusion modification
Authors: Cole D. P. , Bruck H. A. , Roytburd A. L.
Published: March 2008

Graded shape memory alloy thin films were fabricated and characterized to study the effects of compositional gradients on elastic modulus and hardness measurements. Ni47Ti53(at.%) films of varying thickness were deposited onto Ni56Ti44 substrates using dc magnetron sputtering. The films were annealed, producing a compositional gradient across the film-substrate interface through diffusion modification. Nanoindentation measurements were used to characterize the mechanical properties at various depths relative to the film-substrate interface. Before annealing, the dependence of elastic modulus and hardness on relative indentation depth was self-similar for films of different thicknesses due to substrate effects of a two layer system. Annealing allows the diffusion across the film-substrate interface to fully or partially penetrate the film, depending on the thickness of the sputtered layer. The fully penetrated thinner annealed films also display the self-similar behavior of a two layer system. This self-similarity deviates for annealed films thicker than approximately 500nm where partial penetration has effectively created a three layer system. This characteristic length is used to estimate a diffusion coefficient on the order of 10−16m2s−1, which is consistent with previously reported values. The proposed technique has the potential to characterize general graded film systems.
Origin of the refractive-index increase in laser-written waveguides in glasses
Authors: Ponader Carl W. , Schroeder Joseph F. , Streltsov Alexander M.
Published: March 2008

We present firm evidence that the mechanism for the refractive-index increase in fused silica caused by irradiation with ultrafast intense laser pulses is the densification of glass. This conclusion is based on the correlation observed between the refractive-index values in waveguides in silica produced by focused femtosecond laser pulses and the shift of the central frequency of ω4 (TO) band (Si–O stretching mode) in micro-Raman spectra. These data were compared with the relation of the Raman shift to density and to refractive index changes in glasses modified by high pressure or irradiation. We conclude that the measured refractive-index increase in silica waveguides can be explained by densification of glass and exclude other hypothesis such as fictive-temperature effect, color center formation, etc.
Hyperincursive discrete harmonic oscillator
Authors: Antippa Adel F. , Dubois Daniel M.
Published: March 2008

The hyperincursive algorithm for the discrete harmonic oscillator is perfectly stable and energy conserving. By identifying the natural parameters of the system, we transform the algorithm into a normal formalism based on dynamic equations of motion. We find that the simultaneous difference equations of motion are complex, that the natural parameters are classical analogs of the quantum mechanical creation and annihilation operators, and that the solution is of utmost simplicity. The methodology is applicable to any dynamical system, has conceptual importance for discrete physics, and practical utility for numerical simulations.
The free energies of six-vertex models and the n-equivalence relation
Authors: Minami Kazuhiko
Published: March 2008

The free energies of six-vertex models on a general domain D with various boundary conditions are investigated with the use of the n-equivalence relation, which help classify the thermodynamic limit properties. It is derived that the free energy of the six-vertex model on the rectangle is unique in the limit (height,width)→(∞,∞). It is derived that the free energies of the model on the domain D are classified through the densities of left∕down arrows on the boundary. Specifically, the free energy is identical to that obtained by Lieb [Phys. Rev. Lett. 18, 1046 (1967); 19, 108 (1967); Phys. Rev. 162, 162 (1967)] and Sutherland [Phys. Rev. Lett 19, 103 (1967)] with the cyclic boundary condition when the densities are both equal to 12. This fact explains several results already obtained through the transfer matrix calculation. The relation to the domino tiling (or dimer, or matching) problems is also noted.
P-induced nanocrystallite dispersion in amorphous-nanocrystalline mixed-phase Si:H thin films
Authors: Jiang C.-S. , Yan B. , Yan Y. , Teplin C. W. , Reedy R. , Moutinho H. R. , Al-Jassim M. M. , Yang J.
Published: March 2008

The effects of P doping on the nanocrystalline formation in mixed-phase Si:H thin films were investigated using secondary-ion mass spectrometry, Raman spectroscopy, atomic force microscopy, cross-sectional transmission electron microscopy, and scanning Kelvin probe microscopy. We found that Si nanocrystallites in the intrinsic and weakly P-doped materials aggregate to form cone-shaped structures. The local workfunction of the nanocrystalline aggregation areas is larger than the surrounding amorphous areas. Increasing the P-doping level requires an increased hydrogen dilution to reach the similar Raman crystallinity. The nanocrystalline aggregation disappears in the heavily P-doped materials, but isolated nancrystallites appear. The effect of P-doping on the nanostructure is explained with the coverage of P-related radicals on the existing nanocrystalline surface during the deposition and the P segregation in grain boundaries, which prevent new nucleation on the surface of existing nanocrystallites.
Dissociation and ionization of the methane molecule by nonrelativistic electrons including the near threshold region
Authors: Erwin Daniel A. , Kunc Joseph A.
Published: March 2008

Several ionization and dissociation channels of electron interaction with the methane molecule are studied using the recently discovered robust scaling law [D. A. Erwin and J. A. Kunc, Phys. Rev. A 72, 052719 (2005)], other experimentally observed relationships between the ionization and dissociation channels, and the most recent information about the processes. The resulting cross sections for the channels are given in the form of analytical expressions valid at all nonrelativistic energies.
Long-range electron transport in a self-organizing n-type organic material
Authors: Duzhko V. , Aqad E. , Imam M. R. , Peterca M. , Percec V. , Singer K. D.
Published: March 2008

Nondispersive time-of-flight electron transport has been observed in a self-organizing perylene diimide derivative, (3,4,5Pr)12G1-3-perylenetetracarboxyldiimide, yielding long-range transport mechanisms that correlate with molecular packing in several structural phases. The consistency of temperature and electric field dependences of electron mobility in the isotropic and columnar Φh1 phases with static rather than dynamic disorder formalisms provides a link between molecular packing, energetic and positional disorders, and magnitudes of mobility.
Evidences of the simultaneous presence of bow-tie and diamond scars in rare-earth doped amorphous silicon microstadium resonators
Authors: Figueira D. S. L. , Frateschi N. C.
Published: March 2008

Microdisks and microstadium resonators were fabricated on erbium doped amorphous hydrogenated silicon (a-Si:H⟨Er⟩) layers sandwiched in air and native SiO2 on Si substrates. Annealing condition is optimized to allow large emission at 1550nm for samples with erbium concentrations as high as 1.02×1020atoms∕cm3. Near field scanning optical microscopy shows evidence of the simultaneous presence of bow-tie and diamond scars. These modes indicate the high quality of the resonators and the potentiality for achieving amorphous silicon microcavity lasers.
Mean-field density-functional model of a second-order wetting transition
Authors: Koga K. , Widom B.
Published: March 2008

First- and second-order wetting transitions are contrasted. A mean-field density-functional model that leads to a second-order transition is introduced. The way in which it differs from an earlier, otherwise similar model in which the transition is first order is noted. The interfacial and line tensions in the model are obtained numerically and their behavior on approach to the transition is determined. The spatial variation of the model’s densities in the neighborhood of the contact line near the wetting transition is also found and seen to be characteristically different at a second-order transition from what it is at a first-order transition. The results for the line tension and for the spatial variation of the densities are in accord with those from an earlier interface-displacement model of the same phenomena.
Low frequency divergence of the dielectric constant and signature of the Meyer–Neldel rule in the ac conductivity of PbS and PbS:Mn nanorods in polymer
Authors: Mandal A. R. , Kabir L. , Mandal S. K.
Published: March 2008

We report here the temperature (130–296K) and frequency (100Hz–1MHz) dependent dielectric study for PbS and PbS:Mn nanorods of diameter ∼30nm grown in polymer matrix. The frequency dependent capacitance data show the divergence of capacitance in the low frequency regime below a cutoff frequency ∼20kHz, above which it is fairly constant or slowly varying with frequency. The temperature variation of ac conductivity data for such quasi-one-dimensional nanorods reveals the signature of correlated barrier hopping transport in the framework of the Meyer–Neldel rule. We also extend our discussion for Mn doped PbS nanorods to get insight into the effect of magnetic doping on the dielectric properties.
Stabilization of mesoporous silica films using multiple organosilanes
Authors: Singh Binay , Gandhi Darshan D. , Singh Amit P. , Moore Richard , Ramanath G.
Published: March 2008

Mesoporous silica (MPS) thin films are attractive for electrically isolating Cu wiring in nanodevices. While porosity is conducive for realizing low-dielectric permittivity k necessary for low signal propagation delays, it renders the MPS susceptible to moisture uptake and metal diffusion. Here, we show that passivating MPS with more than one organosilane with different molecular termini provides several fold greater protection against such instabilities than improvements observed by functionalizing MPS with either type of organosilane individually. MPS films functionalized with bis[3-(triethoxysilyl)propyl] tetrasulfide (BTPTS) and trimethylchlorosilane (TMCS) exhibit at least three orders of magnitude greater time to dielectric breakdown. Bias thermal annealing and infrared spectroscopy measurements indicate that the increased stability is due to Cu blocking by the tetrasulfide groups in BTPTS and decreased moisture uptake is caused by hydrophobic passivation with TMCS. These findings are germane for realizing high-stability low k dielectrics for nanodevice architectures.
Dipole and quadrupole moment functions of the hydrogen halides HF, HCl, HBr, and HI: A Hirshfeld interpretation
Authors: Harrison James F.
Published: March 2008

The dipole and quadrupole moment functions of the hydrogen halides are calculated using a large polarized basis and correlated wavefunctions and compared to experiment and previous calculations. These functions are analyzed in terms of local moments constructed using the Hirshfeld method. The dipole moment is the sum of the functions qHR+μH and μX with qH being the charge on the hydrogen atom, R the internuclear separation, μH and μX the atomic dipoles on the hydrogen and halogen atoms. We find that qHR+μH is always positive and has a maximum at bond lengths larger than the equilibrium. In HF, μF is slightly positive at the maximum in qHR+μH and has little effect on the resultant maximum in the dipole moment function (DMF). μCl, μBr, and μI, on the other hand, are increasingly more negative at the maximum of qHR+μH and have a profound effect on the width of the maximum of the resulting DMF, successively broadening it and completely eliminating it at HI. The quadrupole moment function (QMF) (with the halogen as origin) is given by Θ(HX)=ΘHXproto+δΘX+δΘH+2μHR+qHR2, where ΘHXproto is the quadrupole moment of the separated atoms (the halogen in this instance) and δΘX+δΘH the change in the in situ quadrupole moments of the halogen and hydrogen atoms. The maximum in the QMF and its slope at equilibrium are determined essentially by 2μHR+qHR2, which is known once the DMF is known. δΘX+δΘH is always negative while ΘHXproto is positive, so one can approximate the molecular quadrupole moment to within 10% as Θ(HX)>ΘHXproto+2μHR+qHR2.
Self-organization of epitaxial La0.35Pr0.275Ca0.375MnO3 manganite nanorods on NdGaO3 substrates
Authors: He Jiaqing , Zheng Jin-Cheng , Zhu Yimei , Chaudhuri S. , Budhani R. C.
Published: March 2008

We studied the structure, morphology, and growth mechanism of self-organized La0.35Pr0.275Ca0.375MnO3 manganite nanorods grown on NdGaO3 substrates by pulsed-laser deposition. A two-layered structure was revealed: the first layer, about 120nm thick, was formed via layer-by-layer two-dimensional (2D) growth; the second layer consisted of a three-dimensional assembly of nanorods lying perpendicular to the 2D layer. The nanorods, averaging 50nm across and 180nm long, exhibited six crystallographic orientational domains, but only two predominated, both with their b axis lying parallel to that of substrate (parallel to the film normal) and with an in-plane a- and c-axis interchange to minimize local lattice mismatch. We consider that the formation of such self-assembled nanorods is related to the Stranski–Krastanov growth mode and discuss the associated energy terms of such growth based on density functional theory calculations.
Positive colossal magnetoresistance effect in ZnO∕La0.7Sr0.3MnO3 heterostructure
Authors: Jin K. X. , Zhao S. G. , Chen C. L. , Wang J. Y. , Luo B. C.
Published: March 2008

In this letter, an oxide heterostructure has been fabricated by successively growing La0.7Sr0.3MnO3 and ZnO layers on a LaAlO3 (100) substrate using pulsed laser deposition. The ZnO∕La0.7Sr0.3MnO3 heterostructure exhibits good rectifying behavior and a positive colossal magnetoresistance (MR) effect over a temperature range of 77–280K. The maximum MR values are determined to be about 53.9% at H=0.5T and 36.4% at H=0.3T. A possible explanation is given in terms of the effect of magnetic fields on the depletion layer and the capture carriers effect at the interface.
Pulsed field induced magnetization switching in (Ga,Mn)As
Authors: Li Z. , Mol J. A. , Lagae L. , Borghs G. , Mertens R. , Van Roy W.
Published: March 2008

Up to now, all high frequency switching experiments on ferromagnetic semiconductors have involved light induced switching, which is not compatible with integrated circuits. We employed all-electrical techniques to study the response of (Ga,Mn)As to a magnetic field pulse. A field pulse was applied through a coplanar waveguide and the magnetization was read out by anisotropic magnetoresistance. We demonstrated that full magnetization switching by domain wall nucleation and propagation can be triggered by pulses as short as 800ps, combining the effect of the pulsed field and a heat-induced reduction of the coercive field.
Terahertz radiation from Er,O-codoped GaAs surface grown by organometallic vapor phase epitaxy
Authors: Shimada K. , Terai Y. , Takemoto S. , Hidaka K. , Fujiwara Y. , Suzuki M. , Tonouchi M.
Published: March 2008

Ultrafast carrier dynamics and terahertz radiation from Er,O-codoped GaAs (GaAs:Er,O) have been investigated by pump and probe reflectance and time-domain terahertz spectroscopy. In pump and probe reflectance measurements, GaAs:Er,O showed faster relaxation time (0.37–0.56ps) of photoexcited carriers than undoped GaAs. In terahertz spectroscopy, the radiated terahertz amplitude decreased and the decay time of transient photocurrent became long with increasing Er concentration. The Er concentration dependence was understood by additional electron scattering due to the Er doping. The fast relaxation time and the terahertz radiation properties suggest new applications of GaAs:Er,O for the terahertz frequency region.
Linewidth measurement of external grating cavity quantum cascade laser using saturation spectroscopy
Authors: Mukherjee Nandini , Go Rowel , Patel C. Kumar N.
Published: March 2008

A room temperature external grating cavity (EGC) quantum cascade laser (QCL) is characterized using saturation spectroscopy of NO2. The presence of two strong EGC QCL waveguide modes is evident from the saturation spectra. A linewidth of 21MHz for each EGC-QCL mode is measured from the width of the saturation peak at 10mTorr pressure of NO2.
Enhancement of the upconversion radiation in Y2O3:Er3+ nanocrystals by codoping with Li+ ions
Authors: Chen G. Y. , Liu H. C. , Somesfalean G. , Sheng Y. Q. , Liang H. J. , Zhang Z. G. , Sun Q. , Wang F. P.
Published: March 2008

We report on an innovative route to increase the upconversion (UC) green radiation by two orders of magnitude in Y2O3:Er3+ nanocrystals through tailoring Er3+ ions’ local environment with Li+ ions under diode laser excitation of 970nm. Theoretical investigations based on the steady-state rate equations indicate that such enhancement arises from a combining effect of the tailored lifetime of the intermediate I11∕24(Er) state, the suppressed cross relaxation H11∕22(Er)+I15∕24(Er)→I9∕24(Er)+I13∕24(Er) process, and the enlarged nanocrystal size induced by the Li+ ions. The proposed route here may constitute a promising step to solve the low efficiency problem in UC materials.
Rapid response mechanism of pi cell
Authors: Sun Yubao , Ma Hongmei , Zhang Zhidong , Fu Guangsheng
Published: March 2008

The rapid response mechanism of pi cell is investigated in detail using one elastic constant and small angle approximation. The improving times of the decay time for pi cell driven by undershoot and normal method compared with that for a Freedericksz cell are calculated and it decreases with the increasing driven voltage for the undershoot method but is larger than that for the normal method. The author’s results show that the same gray-to-gray response times can be obtained using undershoot method but cannot using normal method.
Characterization of ZnO nanoparticles by resonant Raman scattering and cathodoluminescence spectroscopies
Authors: Yoshikawa M. , Inoue K. , Nakagawa T. , Ishida H. , Hasuike N. , Harima H.
Published: March 2008

We have measured the Raman and cathodoluminescence (CL) spectra of ZnO nanoparticles with different crystallite sizes. The Raman spectra show that the frequency of the E2 (high) phonon in these nanoparticles, which is initially high, decreases with the crystallite size, while its linewidth increases. This result is explained by the size effect. The CL spectra show that the relative intensity ratio of the CL peak at around 500–600nm to the band-edge CL peak at approximately 360nm drastically increases as the crystallite size decreases. We use the surface recombination model to explain this result. According to this model, the relative intensity ratio increases because of an increase in the concentration of deep levels on the surface of the crystallites and/or an increase in the free-carrier concentration.
Combinatorial measurements of Hall effect and resistivity in oxide films
Authors: Clayhold J. A. , Kerns B. M. , Schroer M. D. , Rench D. W. , Logvenov G. , Bollinger A. T. , Bozovic I.
Published: March 2008

A system for the simultaneous measurement of the Hall effect in 31 different locations as well as the measurement of the resistivity in 30 different locations on a single oxide thin film grown with a composition gradient is described. Considerations for designing and operating a high-throughput system for characterizing highly conductive oxides with Hall coefficients as small as 10−10m3∕C are discussed. Results from measurements on films grown using combinatorial molecular beam epitaxy show the usefulness of characterizing combinatorial libraries via both the resistivity and the Hall effect.
Absolute evaluation of out-of-band radiation from laser-produced tin plasmas for extreme ultraviolet lithography
Authors: Sakaguchi Hirokazu , Fujioka Shinsuke , Namba Shinichi , Tanuma Hajime , Ohashi Hayato , Suda Shintaro , Shimomura Masashi , Nakai Yuki , Kimura Yasuko , Yasuda Yuzuri , Nishimura Hiroaki , Norimatsu Takayoshi , Sunahara Atsushi , Nishihara Katsunobu , Miyanaga Noriaki , Izawa Yasukazu , Mima Kunioki
Published: March 2008

Out-of-band (OOB) radiation (at wavelengths longer than 130nm) from an extreme ultraviolet (EUV) light source reduces the precision of lithography. The energy of the OOB radiation from laser-produced Sn plasmas were measured by using an absolutely calibrated transmission grating spectrometer equipped with a charge-coupled device. The dependence of the OOB radiant energy on the mass and size of the tin fuel was clarified. The dominant source of the OOB radiation is peripheral heating around the laser spot via electron thermal conduction and radiation from the high-temperature EUV emission region.
Experimental measurement of the elastic constants of GdScO3 via resonant ultrasound spectroscopy utilizing ab initio calculations
Authors: Pestka K. A. , Maynard J. D. , Soukiassian A. , Xi X. X. , Schlom D. G. , Le Page Y. , Bernhagen M. , Reiche P. , Uecker R.
Published: March 2008

The complete elastic tensor of single crystal GdScO3 was determined using resonant ultrasound spectroscopy (RUS) in combination with ab initio calculations. The experimental determination of all nine elastic constants also provides a method for probing the dynamic lattice properties for this recently developed orthorhombic material. The experimentally determined elastic constants differed from theoretical values on average by 10%, and all but three of the nine elastic constants varied by less than 10%. These results indicate that ab initio calculations are now sufficiently accurate for the precise determination of the elastic tensor using RUS as the sole experimental source.
Soft glassy rheology of supercooled molecular liquids
Authors: Zondervan Rob , Xia Ted , van der Meer Harmen , Storm Cornelis , Kulzer Florian , van Saarloos Wim , Orrit Michel
Published: March 2008

We probe the mechanical response of two supercooled liquids, glycerol and
ortho
-terphenyl, by conducting rheological experiments at very weak stresses. We find a complex fluid behavior suggesting the gradual emergence of an extended, delicate solid-like network in both materials in the supercooled state—i.e., above the glass transition. This network stiffens as it ages, and very early in this process it already extends over macroscopic distances, conferring all well known features of soft glassy rheology (yield-stress, shear thinning, aging) to the supercooled liquids. Such viscoelastic behavior of supercooled molecular glass formers is difficult to observe because the large stresses in conventional rheology can easily shear-melt the solid-like structure. The work presented here, combined with evidence for long-lived heterogeneity from previous single-molecule studies [Zondervan R, Kulzer F, Berkhout GCG, Orrit M (2007) Local viscosity of supercooled glycerol near
T
g
probed by rotational diffusion of ensembles and single dye molecules.
Proc Natl Acad Sci USA
104:12628–12633], has a profound impact on the understanding of the glass transition because it casts doubt on the widely accepted assumption of the preservation of ergodicity in the supercooled state.
Regulating continent growth and composition by chemical weathering
Authors: Lee Cin-Ty Aeolus , Morton Douglas M. , Little Mark G. , Kistler Ronald , Horodyskyj Ulyana N. , Leeman William P. , Agranier Arnaud
Published: March 2008

Continents ride high above the ocean floor because they are underlain by thick, low-density, Si-rich, and Mg-poor crust. However, the parental magmas of continents were basaltic, which means they must have lost Mg relative to Si during their maturation into continents. Igneous differentiation followed by lower crustal delamination and chemical weathering followed by subduction recycling are possible solutions, but the relative magnitudes of each process have never been quantitatively constrained because of the lack of appropriate data. Here, we show that the relative contributions of these processes can be obtained by simultaneous examination of Mg and Li (an analog for Mg) on the regional and global scales in arcs, delaminated lower crust, and river waters. At least 20% of Mg is lost from continents by weathering, which translates into >20% of continental mass lost by weathering (40% by delamination). Chemical weathering leaves behind a more Si-rich and Mg-poor crust, which is less dense and hence decreases the probability of crustal recycling by subduction. Net continental growth is thus modulated by chemical weathering and likely influenced by secular changes in weathering mechanisms.
Oncogene cooperation in tumor maintenance and tumor recurrence in mouse mammary tumors induced by
Myc
and mutant
Kras
Authors: Podsypanina Katrina , Politi Katerina , Beverly Levi J. , Varmus Harold E.
Published: March 2008

Most, if not all, cancers are composed of cells in which more than one gene has a cancer-promoting mutation. Although recent evidence has shown the benefits of therapies targeting a single mutant protein, little attention has been given to situations in which experimental tumors are induced by multiple cooperating oncogenes. Using combinations of doxycycline-inducible and constitutive
Myc
and mutant
Kras
transgenes expressed in mouse mammary glands, we show that tumors induced by the cooperative actions of two oncogenes remain dependent on the activity of a single oncogene. Deinduction of either oncogene individually, or both oncogenes simultaneously, led to partial or complete tumor regression. Prolonged remission followed deinduction of
Kras

G12D

in the context of continued
Myc
expression, deinduction of a
MYC
transgene with continued expression of mutant
Kras
produced modest effects on life extension, whereas simultaneous deinduction of both
MYC
and
Kras

G12D

transgenes further improved survival. Disease relapse after deinduction of both oncogenes was associated with reactivation of both oncogenic transgenes in all recurrent tumors, often in conjunction with secondary somatic mutations in the tetracycline transactivator transgene,
MMTV-rtTA
, rendering gene expression doxycycline-independent. These results demonstrate that tumor viability is maintained by each gene in a combination of oncogenes and that targeted approaches will also benefit from combination therapies.
Book Review
Authors: Nakstad Per Hj.
Published: March 2008

Brain Imaging. By K. Sartor, S. Haehnel and B. Kress. Stuttgart and New York: Thieme Verlag, 2007. ISBN 9781588905703. 300 pages, 336 illustrations. Price paperback: EUR 44.95
Discerning the Division of Cognitive Labor: An Emerging Understanding of How Knowledge Is Clustered in Other Minds
Authors: Keil Frank C. , Stein Courtney , Webb Lisa , Billings Van Dyke , Rozenblit Leonid
Published: March 2008

The division of cognitive labor is fundamental to all cultures. Adults have a strong sense of how knowledge is clustered in the world around them and use that sense to access additional information, defer to relevant experts, and ground their own incomplete understandings. One prominent way of clustering knowledge is by disciplines similar to those that comprise the natural and social sciences. Seven studies explored an emerging sense of these discipline‐based ways of clustering of knowledge. Even 5‐year‐olds could cluster knowledge in a manner roughly corresponding to the departments of natural and social sciences in a university, doing so without any explicit awareness of those academic disciplines. But this awareness is fragile early on and competes with other ways of clustering knowledge. Over the next few years, children come to see discipline‐based clusters as having a privileged status, one that may be linked to increasingly sophisticated assumptions about essences for natural kinds. Possible mechanisms for this developmental shift are examined.
Understanding and Using Principles of Arithmetic: Operations Involving Negative Numbers
Authors: Prather Richard W. , Alibali Martha W.
Published: March 2008

Previous work has investigated adults' knowledge of principles for arithmetic with positive numbers (). The current study extends this past work to address adults' knowledge of principles of arithmetic with a negative number, and also investigates links between knowledge of principles and problem representation. Participants (N = 44) completed two tasks. In the Evaluation task, participants rated how well sets of equations were solved. Some sets violated principles of arithmetic and others did not. Participants rated non‐violation sets higher than violation sets for two different principles for subtraction with a negative number. In the Word Problem task, participants read word problems and set up equations that could be used to solve them. Participants who displayed greater knowledge of principles of arithmetic with a negative number were more likely to set up equations that involved negative numbers. Thus, participants' knowledge of arithmetic principles was related to their problem representations.
Protein for adaptations to exercise training
Authors: Tipton Kevin D.
Published: March 2008

Nutrient intake before, during, and after training will influence the adaptations that occur in response to the training stimulus. The influence of protein on training adaptations is receiving increasing attention from researchers. Methodological issues should be carefully considered when evaluating evidence of nutritional influence on training adaptations. Evidence suggests that adaptations to training are due to changes in the types and activities of various proteins in response to each exercise bout. Thus, study of the acute metabolic and molecular responses to exercise plus nutrition may provide valuable information about the expected influence on training adaptations. The type of protein, timing of protein ingestion relative to exercise, concurrent ingestion of other nutrients with protein, as well as the type of exercise training performed will impact the adaptations to training with the intake of protein. Protein is an important nutrient for muscle hypertrophy with training, but there is little support for the need for very high (e.g. >2.5–3.0 grams of protein per kilogram of body weight) intakes. Traditionally, endurance athletes have focused on carbohydrate intake, but recently protein has been touted to be critical during and after endurance exercise. There is evidence for and against the importance of protein for endurance exercise and more, well‐controlled studies are required to delineate the importance of protein for endurance exercise adaptations. Whereas nutritional manipulations have customarily been focused on preventing protein degradation, muscle damage, and oxidative stress, recent evidence suggests that these processes may be critical for the optimal adaptive response to training.
Somatically acquired JAK1 mutations in adult acute lymphoblastic leukemia
Authors: Flex Elisabetta , Petrangeli Valentina , Stella Lorenzo , Chiaretti Sabina , Hornakova Tekla , Knoops Laurent , Ariola Cristina , Fodale Valentina , Clappier Emmanuelle , Paoloni Francesca , Martinelli Simone , Fragale Alessandra , Sanchez Massimo , Tavolaro Simona , Messina Monica , Cazzaniga Giovanni , Camera Andrea , Pizzolo Giovanni , Tornesello Assunta , Vignetti Marco , Battistini Angela , Cavé Hélène , Gelb Bruce D. , Renauld Jean-Christophe , Biondi Andrea , Constantinescu Stefan N. , Foà Robin , Tartaglia Marco
Published: March 2008

Aberrant signal transduction contributes substantially to leukemogenesis. The Janus kinase 1 (JAK1) gene encodes a cytoplasmic tyrosine kinase that noncovalently associates with a variety of cytokine receptors and plays a nonredundant role in lymphoid cell precursor proliferation, survival, and differentiation. We report that somatic mutations in JAK1 occur in individuals with acute lymphoblastic leukemia (ALL). JAK1 mutations were more prevalent among adult subjects with the T cell precursor ALL, where they accounted for 18% of cases, and were associated with advanced age at diagnosis, poor response to therapy, and overall prognosis. All mutations were missense, and some were predicted to destabilize interdomain interactions controlling the activity of the kinase. Three mutations that were studied promoted JAK1 gain of function and conferred interleukin (IL)-3–independent growth in Ba/F3 cells and/or IL-9–independent resistance to dexamethasone-induced apoptosis in T cell lymphoma BW5147 cells. Such effects were associated with variably enhanced activation of multiple downstream signaling pathways. Leukemic cells with mutated JAK1 alleles shared a gene expression signature characterized by transcriptional up-regulation of genes positively controlled by JAK signaling. Our findings implicate dysregulated JAK1 function in ALL, particularly of T cell origin, and point to this kinase as a target for the development of novel antileukemic drugs.
Technology/Ideology: How Ideological Fields Influence Consumers' Technology Narratives
Authors: Kozinets Robert V.
Published: March 2008

Through a systematic study of consumer narratives, this article models how technology ideologies influence consumer-level thought, speech, and action. Applying critical discourse analysis and articulation theory approaches, a semiotic square model represents the relations between Techtopian, Green Luddite, Work Machine, and Techspressive ideological elements in an ideological field. The narratives of individual consumers move between ideological elements in ways suggested by the model's semantic relations. The results reveal novel aspects of consumers' dynamic relations to technology ideology and invite further investigations of technology and consumption ideology.
Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment
Authors: Guo Dai-shi , Ma Zi-feng , Yin Chun-sheng , Jiang Qi-zhong
Published: March 2008

TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Bronsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.
Theoretical Study on Mechanism of Reaction of OH with HO2NO2
Authors: Tian Yan , He Tian-jing , He Li , Liu Fan-chen , Chen Dong-ming
Published: March 2008

The reaction of HO2NO2 (peroxynitric acid, PNA) with OH was studied by the hybrid density functional B3LYP and CBS-QB3 methods. Based on the calculated potential energy surface, five reaction channels, H2O+NO2+O2, HOOH+NO3, NO2+HO3H, HO2+HONO2 and HO2+HOONO, were examined in detail. The major reaction channel is PNA+OHM1TS1H2O+NO2+O2. Taking a pre-equilibrium approximation and using the CBS-QB3 energies, the theoretical rate constant of this channel was calculated as 1.13 1012 cm3/(molecule s) at 300 K, in agreement with the experimental result. Comparison between reactions of HOONO2+OH and HONO2+OH was carried out. For HOR+OH reactions, the total rate constants increase from R=NO2 to R=ONO2, which is consistent with experimental measurements.
Adsorption of H2O, OH, and O on CuCl(111) Surface: A Density Functional Theory Study
Authors: Wang Xia , Chen Wen-kai , Sun Bao-zhen , Lu Chun-hai
Published: March 2008

The adsorption of H2O molecule and its dissociation products, O and OH, on CuCl(111) surface was studied with periodic slab model by PW91 approach of GGA within the framework of density functional theory. The results of geometry optimization indicate that the top site is stable energetically for H2O adsorbed over the CuCl(111) surface. The threefold hollow site is found to be the most stable adsorption site for OH and O, and the calculated adsorption energies are 309.5 and 416.5 kJ/mol, respectively. Adsorption of H2O on oxygen-precovered CuCl(111) surface to form surface hydroxyl groups is predicted to be exothermic by 180.1 kJ/mol. The stretching vibrational frequencies, Mulliken population analysis and density of states analysis are employed to interpret the possible mechanism for the computed results.
Dynamic Theory of Die Swell for Entangled Polymeric Liquids in Tube Extrusion: Correlations of Total and Ultimate Extrudate Swell Effects to Growth Time, Shear Stress and Aspect Ratio Under the Free States
Authors: Zhao Jing , Song Ming-shi , Zhu Chang-wei , Hu Gui-xian , Wang Ke-jian , Wu Da-ming
Published: March 2008

The dynamic theory of die swell deduced in a previous paper was extensively applied to study the extrudate swelling behaviors of two entangled polymeric liquids (HDPE and PBD) in a simple shear flow at steady shear stress. The mechanism and dynamics for the recoils and the recoveries of viscoelastic strains in the extrudate were investigated under the free recovery and dynamic states. It was found that in the course of recovery the free recoil and the growth of die swell in the extrudate may be divided into two recovery regions (instantaneous and delayed regions) and three growth stages (instantaneous, delayed, and ultimate extrudate swelling stages). The free recoil and the extrudate swelling behaviors may be expressed as a function of shear stress. The correlations of instantaneous, delayed, total and ultimate extrudate swell effects to the molecular parameters and the operational variables in the simple shear flow at steady shear stress were derived from the dynamic theory of die swell. Also, two sets of new universal equations on the total extrudate swelling effect (TESE) and ultimate extrudate swelling effect (UESE) were deduced. The first is the universal equation of the logarithmic correlation between the TESE and the growth time under the free and dynamic states; the second is the universal equation of the logarithmic correlation between the UESE and the operational variables under the free and equilibrium states. The first equation was verified by experimental data of PBD with different molecular weights at different operational variables. The second equation was verified by experimental data of HDPE at two temperatures and different operational variables. An excellent agreement result was obtained. The excellent agreement shows that the two universal equations can be used directly to predict the correlations of the TESE and UESE to the growth time, the molecular parameters, and the operational variables under the dynamic and equilibrium states.
Scaffolding and validation of bacterial genome assemblies using optical restriction maps
Authors: Nagarajan Niranjan , Read Timothy D. , Pop Mihai
Published: March 2008

Motivation: New, high-throughput sequencing technologies have made it feasible to cheaply generate vast amounts of sequence information from a genome of interest. The computational reconstruction of the complete sequence of a genome is complicated by specific features of these new sequencing technologies, such as the short length of the sequencing reads and absence of mate-pair information. In this article we propose methods to overcome such limitations by incorporating information from optical restriction maps.

Results: We demonstrate the robustness of our methods to sequencing and assembly errors using extensive experiments on simulated datasets. We then present the results obtained by applying our algorithms to data generated from two bacterial genomes Yersinia aldovae and Yersinia kristensenii. The resulting assemblies contain a single scaffold covering a large fraction of the respective genomes, suggesting that the careful use of optical maps can provide a cost-effective framework for the assembly of genomes.

Availability: The tools described here are available as an open-source package at ftp://ftp.cbcb.umd.edu/pub/software/soma

Contact:  mpop@umiacs.umd.edu