bluuebunny/crossref_metadata_2025 huggingface dataset:
Radius dependent shift in surface plasmon frequency in large metallic nanospheres: Theory and experiment
Authors: Jacak W. , Krasnyj J. , Jacak J. , Gonczarek R. , Chepok A. , Jacak L. , Hu D. Z. , Schaadt D.
Published: June 2010

Theoretical description of oscillations of electron liquid in large metallic nanospheres (with radius of few tens of nanometer) is formulated within random-phase-approximation semiclassical scheme in jellium model with retardation included via Lorentz friction. Spectrum of plasmons is determined including both surface and volume type excitations. It is demonstrated that only surface plasmons of dipole type can be excited by homogeneous dynamical electric field. The Lorentz friction due to irradiation of electromagnetic wave by plasmon oscillations is analyzed with respect to the sphere dimension. The resulting shift in resonance frequency turns out to be strongly sensitive to the sphere radius. The form of electromagnetic (e-m) response of the system of metallic nanospheres embedded in the dielectric medium is found. The theoretical predictions are verified by a measurement of extinction of light due to plasmon excitations in nanosphere colloidal water solutions, for Au and Ag metallic components with radius from 10 to 75 nm. Theoretical predictions and experiments clearly agree in the positions of surface plasmon resonances and in an emergence of the first volume plasmon resonance in the e-m response of the system for limiting big nanosphere radii, when dipole approximation is not exact.
Calculation of electromagnetic force in electromagnetic forming process of metal sheet
Authors: Xu Da , Liu Xuesong , Fang Kun , Fang Hongyuan
Published: June 2010

Electromagnetic forming (EMF) is a forming process that relies on the inductive electromagnetic force to deform metallic workpiece at high speed. Calculation of the electromagnetic force is essential to understand the EMF process. However, accurate calculation requires complex numerical solution, in which the coupling between the electromagnetic process and the deformation of workpiece needs be considered. In this paper, an appropriate formula has been developed to calculate the electromagnetic force in metal work-piece in the sheet EMF process. The effects of the geometric size of coil, the material properties, and the parameters of discharge circuit on electromagnetic force are taken into consideration. Through the formula, the electromagnetic force at different time and in different positions of the workpiece can be predicted. The calculated electromagnetic force and magnetic field are in good agreement with the numerical and experimental results. The accurate prediction of the electromagnetic force provides an insight into the physical process of the EMF and a powerful tool to design optimum EMF systems.
Theory of interfacial orientational relaxation spectroscopic observables
Authors: Gengeliczki Zsolt , Rosenfeld Daniel E. , Fayer M. D.
Published: June 2010

The orientational correlation functions measured in the time-resolved second-harmonic generation (TRSHG) and time-resolved sum-frequency generation (TRSFG) experiments are derived. In the laboratory coordinate system, the ⟨Ylm(Ωlab(t))Y2m(Ωlab(0))⟩ (l=1,3 and m=0,2) correlation functions, where the Ylm are spherical harmonics, describe the orientational relaxation observables of molecules at interfaces. A wobbling-in-a-cone model is used to evaluate the correlation functions. The theory demonstrates that the orientational relaxation diffusion constant is not directly obtained from an experimental decay time in contrast to the situation for a bulk liquid. Model calculations of the correlation functions are presented to demonstrate how the diffusion constant and cone half-angle affect the time-dependence of the signals in TRSHG and TRSFG experiments. Calculations for the TRSHG experiments on Coumarin C314 molecules at air-water and air-water-surfactant interfaces are presented and used to examine the implications of published experimental results for these systems.
Sample cells for probing solid/liquid interfaces with broadband sum-frequency-generation spectroscopy
Authors: Verreault Dominique , Kurz Volker , Howell Caitlin , Koelsch Patrick
Published: June 2010

Two sample cells designed specifically for sum-frequency-generation (SFG) measurements at the solid/liquid interface were developed: one thin-layer analysis cell allowing measurement of films on reflective metallic surfaces through a micrometer layer of solution and one spectroelectrochemical cell allowing investigation of processes at the indium tin oxide/solution interface. Both sample cells are described in detail and data illustrating the capabilities of each are shown. To further improve measurements at solid/liquid interfaces, the broadband SFG system was modified to include a reference beam which can be measured simultaneously with the sample signal, permitting background correction of SFG spectra in real time. Sensitivity tests of this system yielded a signal-to-noise ratio of 100 at a surface coverage of 0.2 molecules/nm2. Details on data analysis routines, pulse shaping methods of the visible beam, as well as the design of a purging chamber and sample stage setup are presented. These descriptions will be useful to those planning to set up a SFG spectrometer or seeking to optimize their own SFG systems for measurements of solid/liquid interfaces.
Note: Rigid holder to host and bend a crystal for multiple volume reflection of a particle beam
Authors: Carassiti V. , Dalpiaz P. , Guidi V. , Mazzolari A. , Melchiorri M.
Published: June 2010

A holder to lodge and bend a silicon crystal to excite multivolume reflection of a high-energy particle beam has been designed and fabricated. A mechanically robust and stable structure fastens a crystal at best condition for experiments. The holder has allowed the observation of 12-time repeated volume reflection with very high efficiency. We detail the most important features behind the construction of the holder together with the characterization of the crystal being bent by the holder.
Quantifying the transfer and settling in NMR experiments with sample shuttling
Authors: Granwehr Josef , Panek Rafal , Leggett James , Köckenberger Walter
Published: June 2010

Nuclear magnetic resonance (NMR) in combination with pulsed magnetic field gradients has proven very successful for measuring molecular diffusion, where the correlation time of the motion is much shorter than the timescale of the experiment. In this article, it is demonstrated that a single-scan NMR technique to measure molecular diffusion can be employed to also study incoherent random motions over macroscopic length scales that show correlation times similar to the timescale of the experiment. Such motions are observed, for example, after the mixing of two components or after transferring a sample from one container into another. To measure the fluid settling, a series of magnetization helices were encoded onto a sample. Stimulated gradient echo trains were then generated after different mixing times, which enabled the determination of an effective dispersion coefficient for the fluid. This technique was used to optimize the timing of NMR experiments combined with dissolution dynamic nuclear polarization, where a sample was shuttled between two magnets. In addition to the decay of fluid turbulences, the presence of microbubbles in the sample tube at the end of the shuttling step was identified as another contribution to the NMR linewidth. Microbubbles could be indirectly observed through the line broadening effect on the NMR signal due to their different susceptibility compared to the solvent, which induced field gradients near the interfaces. Using these data, the signal attenuation caused by sample motion in single-scan two-dimensional correlation spectroscopy NMR experiments could be predicted with reasonable accuracy.
Lyapunov spectra and conjugate-pairing rule for confined atomic fluids
Authors: Bernardi Stefano , Todd B. D. , Hansen J. S. , Searles Debra J. , Frascoli Federico
Published: June 2010

In this work we present nonequilibrium molecular dynamics simulation results for the Lyapunov spectra of atomic fluids confined in narrow channels of the order of a few atomic diameters. We show the effect that realistic walls have on the Lyapunov spectra. All the degrees of freedom of the confined system have been considered. Two different types of flow have been simulated: planar Couette flow and planar Poiseuille flow. Several studies exist on the former for homogeneous flows, so a direct comparison with previous results is performed. An important outcome of this work is the demonstration of how the spectrum reflects the presence of two different dynamics in the system: one for the unthermostatted fluid atoms and the other one for the thermostatted and tethered wall atoms. In particular the Lyapunov spectrum of the whole system does not satisfy the conjugate-pairing rule. Two regions are instead distinguishable, one with negative pairs’ sum and one with a sum close to zero. To locate the different contributions to the spectrum of the system, we computed “approximate” Lyapunov exponents belonging to the phase space generated by the thermostatted area and the unthermostatted area alone. To achieve this, we evolved Lyapunov vectors projected into a reduced dimensional phase space. We finally observe that the phase-space compression due to the thermostat remains confined into the wall region and does not significantly affect the purely Newtonian fluid region.
Nonequilibrium numerical model of homogeneous condensation in argon and water vapor expansions
Authors: Jansen Ryan , Wysong Ingrid , Gimelshein Sergey , Zeifman Michael , Buck Udo
Published: June 2010

A computational approach capable of modeling homogeneous condensation in nonequilibrium environments is presented. The approach is based on the direct simulation Monte Carlo (DSMC) method, extended as appropriate to include the most important processes of cluster nucleation and evolution at the microscopic level. The approach uses a recombination-reaction energy-dependent mechanism of the DSMC method for the characterization of dimer formation, and the RRK model for the cluster evaporation. Three-step testing and validation of the model is conducted by (i) comparison of clusterization rates in an equilibrium heat bath with theoretical predictions for argon and water vapor and adjustment of the model parameters, (ii) comparison of the nonequilibrium argon cluster size distributions with experimental data, and (iii) comparison of the nonequilibrium water cluster size distributions with experimental measurements. Reasonable agreement was observed for all three parts of the validation.
Calculation of the first static hyperpolarizability tensor of three-dimensional periodic compounds with a local basis set: A comparison of LDA, PBE, PBE0, B3LYP, and HF results
Authors: Orlando Roberto , Lacivita Valentina , Bast Radovan , Ruud Kenneth
Published: June 2010

The computational scheme for the evaluation of the second-order electric susceptibility tensor in periodic systems, recently implemented in the CRYSTAL code within the coupled perturbed Hartree–Fock (HF) scheme, has been extended to local-density, gradient-corrected, and hybrid density functionals (coupled-perturbed Kohn–Sham) and applied to a set of cubic and hexagonal semiconductors. The method is based on the use of local basis sets and analytical calculation of derivatives. The high-frequency dielectric tensor (ϵ∞) and second-harmonic generation susceptibility (d) have been calculated with hybrid functionals (PBE0 and B3LYP) and the HF approximation. Results are compared with the values of ϵ∞ and d obtained from previous plane-wave local density approximation or generalized gradient approximation calculations and from experiment. The agreement is in general good, although comparison with experiment is affected by a certain degree of uncertainty implicit in the experimental techniques.
Absolute lateral instability in capillary coflowing jets
Authors: Herrada Miguel A. , Ferrera Conrado , Montanero José M. , Gañán-Calvo Alfonso M.
Published: June 2010

We examine the stability of coflowing capillary jets under lateral (m=1) perturbations of small amplitude. Two models are considered for the perturbed basic flow: the Kelvin–Helmholtz (KH) and the outer boundary layer (OBL) models. We revisit the temporal analysis of the KH model and show that the flow is unstable if and only if the (conveniently defined) Weber number is greater than unity. On the contrary, the OBL flow becomes unstable for Weber numbers much smaller than unity, although the growth rate of the perturbations is very small in that case. The spatiotemporal analysis of the dispersion relations shows that both the KH and OBL flows become absolutely unstable (absolute whipping) for sufficiently large values of the Weber number and the ratio between the outer and inner stream velocities. Absolute whipping dominates the behavior of high-viscosity jets for large velocity ratios and prevents the jetting regime from being reached even when varicose perturbations are convected downstream. For sufficiently large values of the Reynolds number, the flow becomes absolutely unstable if the velocity ratio exceeds a critical value, which is almost independent of the Weber number. For small values of the velocity ratio, the flow is stable or at most convectively unstable independently of the Reynolds and Weber numbers. For sufficiently large values of the velocity ratio, there is a critical Reynolds number above which jetting can not be reached because the flow becomes absolutely unstable due to the modes m=0 and/or m=1. That critical Reynolds number decreases as the velocity ratio increases. These results have important implications in technological applications such as steady high-viscosity liquid microjet production and fiber spinning using coflowing gas conformation.
Low-temperature buffer layer effects on the quality of ZnTe epilayers grown on sapphire substrates
Authors: Guo Qixin , Nada Masaki , Ding Yaliu , Tanaka Tooru , Nishio Mitsuhiro
Published: June 2010

The effects of a low-temperature ZnTe buffer layer on the structural, optical properties and surface morphology of ZnTe epilayers grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy are investigated. X-ray diffraction, x-ray rocking curves, photoluminescence spectra, Raman spectra, and atomic force microscopy analysis reveal that the crystal quality, optical properties, and surface roughness of ZnTe epilayers can be improved by introducing a low-temperature ZnTe buffer layer between ZnTe epilayer and sapphire substrate, and that the thickness of the low-temperature ZnTe buffer layer is critical for obtaining a high quality ZnTe epilayer.
Properties and etching rates of negative ions in inductively coupled plasmas and dc discharges produced in Ar/SF6
Authors: Draghici M. , Stamate E.
Published: June 2010

Negative ion production is investigated in a chamber with transversal magnetic filter operated in dc or inductively coupled plasma (ICP) modes in Ar/SF6 gas mixtures. Plasma parameters are evaluated by mass spectrometry and Langmuir probe for different discharge conditions. The density ratio of negative ion to electron exceeded 300 in dc mode while it was below 100 in the ICP mode. The possibility to apply a large positive bias to an electrode without affecting the plasma potential and the transition from a negative sheath to anodic glow are also investigated. The etching rates by positive and negative ions are evaluated on silicon substrate for different Ar/SF6 gas ratios. The etching rate by negative ions was with less than 5% smaller than that by positive ions.
Magnetic field-induced excitation and optical detection of mechanical modes of microspheres
Authors: Ioppolo T. , Ötügen M. V. , Marcis K.
Published: June 2010

We propose a method to excite and detect the mechanical modes of dielectric microspheres. The mechanical modes are excited by simultaneously imposing static and harmonic magnetic fields on the spheres. They are monitored by simultaneously exciting and tracking the whispering gallery optical modes of the spheres. An analysis is carried out to investigate the relationship between the applied magnetic field and the corresponding whispering gallery mode shifts. Experiments were carried out to demonstrate the proposed magnetic field-induced excitation and optical detection method.
Observation of ferromagnetism in PdCo alloy nanoparticles encapsulated in carbon nanotubes
Authors: Roa Daniel Bretas , Barcelos Ingrid David , de Siervo Abner , Pirota Kleber Roberto , Lacerda Rodrigo Gribel , Magalhães-Paniago Rogério
Published: June 2010

Carbon nanotubes terminated by PdCo catalyst nanoparticles were grown by plasma-enhanced chemical vapor deposition. Transmission electron microscopy reveals that these nanoparticles have a droplike shape and are completely encapsulated inside multiwalled nanotubes. Magnetization measurements showed the existence of a permanent magnetization with a small shape anisotropy effect. The magnetization of both cobalt and palladium was confirmed by x-ray magnetic circular dichroism. These results show that nanotubes ended by magnetic PdCo nanoparticles can be grown and could be used in magnetic storage media and electrical spin injection.
Development of a multiplex fast-scan system for ultrafast time-resolved spectroscopy
Authors: Yabushita Atsushi , Lee Yu-Hsien , Kobayashi Takayoshi
Published: June 2010

A fast-scan method was developed to obtain time-resolved signals with femtosecond resolution over a picosecond range on the fly and in real time. Traditional fast-scan methods collect data at each probe wavelength one by one, which is time consuming and thus not possible for the study of photofragile materials. In this work, we have developed a system that performs fast scans with multiplex detection. Ultrafast time-resolved spectroscopy was demonstrated using the newly developed system. Femtosecond laser pulses have been used for pump-probe studies of ultrafast processes in various materials, and both electronic relaxation and vibrational dynamics have been studied. However, experiments have been limited in sensitivity and reliability because they are affected by the long-term instability of the ultrashort laser pulses and by the fragility of the samples. The instability of the sources hinders precise determination of electronic decay dynamics and introduces systematic errors. The fragility of the samples reduces their amount or concentration, and can lead to contamination of the materials even if they were pure before the measurement. These effects make it difficult to obtain reproducible and reliable experimental data. In the present work, we have developed a fast-scan pump-probe spectroscopic system that can complete a set of measurements in less than 2 min. Quantitative estimates of the signal reproducibility demonstrate that these measurements provide higher reproducibility and reliability than conventional measurements.
Charge-density depinning at metal contacts of graphene field-effect transistors
Authors: Nouchi Ryo , Tanigaki Katsumi
Published: June 2010

An anomalous distortion is often observed in the transfer characteristics of graphene field-effect transistors. We fabricate graphene transistors with ferromagnetic metal electrodes, which reproducibly display distorted transfer characteristics, and show that the distortion is caused by metal-graphene contacts with no charge-density pinning effect. The pinning effect, where the gate voltage cannot tune the charge density of graphene at the metal electrodes, has been experimentally observed; however, a pinning-free interface is achieved with easily-oxidizable metals. The distortion should be a serious problem for flexible electronic devices with graphene.
Structural evidence for the nonmonotonic trend of TC in tetragonal PbTiO3BiScO3 solid solutions
Authors: Chen Jun , Nittala Krishna , Jones Jacob L. , Hu Penghao , Xing Xianran
Published: June 2010

High-TC piezoelectric (1−x)PbTiO3xBiScO3 shows a nonmonotonic trend of TC in the tetragonal phase with respect to content of BiScO3. To understand this behavior, the structure of (1−x)PbTiO3xBiScO3 solid solutions is studied by means of neutron powder diffraction. The cation displacements of Pb/Bi and Ti/Sc exhibit a coupling property and a different impact by the substitution content of BiScO3. Its nonmonotonic trend of TC is quantitatively related to the calculated spontaneous polarization in the whole tetragonal range. The unique role of Bi-substitution not only contributes to enhance the component of polarization of Pb/Bi but also to increase the TC.
Diameter dependence of the minority carrier diffusion length in individual ZnO nanowires
Authors: Soudi A. , Dhakal P. , Gu Y.
Published: June 2010

The minority carrier diffusion length, LD, was directly measured in individual ZnO nanowires by a near-field scanning photocurrent microscopy technique. The diameter dependence of LD suggests a diameter-dependent surface electronic structure, particularly an increase in the density of mid-band-gap surface states with the decreasing diameter. This diameter dependence of the surface electronic structure might be a universal phenomenon in wurtzite-type nanostructures, and is critical in interpreting and understanding the effects of surfaces on various material properties.
Miniaturized superconducting metamaterials for radio frequencies
Authors: Kurter Cihan , Abrahams John , Anlage Steven M.
Published: June 2010

We have developed a low-loss, ultrasmall radio frequency (rf) metamaterial operating at ∼76 MHz. This miniaturized medium is made up of planar spiral elements with diameter as small as ∼λ/658 (λ is the free space wavelength), fashioned from Nb thin films on quartz substrates. The transmission data are examined below and above the superconducting transition temperature of Nb for both a single spiral and a one dimensional array. The validity of the design is tested through numerical simulations and good agreement is found. We discuss how superconductors enable such a compact design in the rf with high loaded-quality factor (in excess of 5000), which is in fact difficult to realize with ordinary metals.
Electrical breakdown of ZnO nanowires in metal-semiconductor-metal structure
Authors: Zhang Qi , Qi Junjie , Yang Ya , Huang Yunhua , Li Xin , Zhang Yue
Published: June 2010

We investigated the stability of ZnO nanowires in a metal-semiconductor-metal structure by applying a longitudinal electric field inside a scanning electron microscope equipped with manipulators. The electrical transport was well simulated by the thermionic-field-emission model and the failure of single crystalline ZnO nanowires was directly observed when the applied electric field reached the break point, an electric field intensity of ∼106 V/m. The recrystallization of ZnO nanowires from single crystalline to polycrystalline pearl-like structure in the failure process was also investigated. Experimental results indicated that the failure is attributed to a joint effect of high electric field and Joule heating.
Tunable positive temperature coefficient of resistivity in an electrically conducting polymer/graphene composite
Authors: Pang Huan , Zhang Yi-Chuan , Chen Tao , Zeng Bao-Qing , Li Zhong-Ming
Published: June 2010

The graphene nanosheet (GNS)/ultrahigh molecular weight polyethylene composite with a two-dimensional conductive network of GNSs exhibits an increasing positive temperature coefficient (PTC) of resistivity while thermally treated at a certain temperature. This anomalous phenomenon is originated from the reduced viscosity of polymer matrix, crystallization induced local flow and weak interactions among the overlapping joints of GNSs, which allow GNSs to migrate to the polymer matrix, thus weakening the conductive paths and increasing the PTC intensity. A facile approach is accordingly developed to prepare a conductive polymer composite with a tunable PTC intensity.
Simple models for predicting dead fuel moisture in eucalyptus forests
Authors: Matthews Stuart , Gould Jim , McCaw Lachie
Published: June 2010

Fire behaviour prediction requires models of dead fuel moisture that are both accurate and suitable for use for operational applications. The paper investigates two methods of developing a simple operational fine fuel moisture model from a more complex process-based model. The first simple model is a table of fuel moisture predictions for values of air temperature, relative humidity, wind speed and solar radiation. The second model reduces the original model to a single differential equation, which may be used on low-powered computers. The simple models are tested against the output of the original model and against observations from two case studies in dry eucalyptus forest in south-western Australia. The single differential equation model was capable of reproducing the prediction of the process-based model at all times of the day, with mean error (ME) in predictions of –0.1% and mean absolute error (MAE) of 0.6%. The table model performed less well, with ME = –0.7% and MAE = 1.1% at 1500 hours, and ME = –1.2% and MAE = 3.0% at other times of the day.
Directional annealing-induced texture in melt-spun (Sm12Co88)99Nb1 alloy
Authors: Jayaraman T V , Rogge P , Shield J E
Published: June 2010

Developing texture in nanocrystalline permanent magnet alloys is of significant importance. Directional annealing is shown to produce texture in the permanent magnet alloy (Sm12Co88)99Nb1. Melt spinning produced isotropic grain structures of the hard magnetic metastable SmCo7 phase, with grain sizes of ∼300 nm. Conventional annealing of melt-spun (Sm12Co88)99Nb1 alloy produced Sm2Co17 phase with random crystallographic orientation. Directional annealing of melt-spun (Sm12Co88)99Nb1 alloy, with appropriate combinations of annealing temperature and translational velocity, produced Sm2Co17 phase with (0 0 0 6) in-plane texture, as determined by x-ray diffraction analysis and magnetic measurements. The magnetization results show out-of-plane remanence higher than the in-plane remanence resulting in the degree of ‘magnetic’ texture in the order of 25–40%. Coercivity values above 2 kOe were maintained. The texture development via directional annealing while minimizing exposure to elevated temperatures provides a new route to anisotropic high-energy permanent magnets.
Calculations of Auger intensity versus beam position for a sample with layers perpendicular to its surface
Authors: Zommer L , Jablonski A
Published: June 2010

Recent advances in nanotechnology are a driving force for the improvement of lateral resolution in advanced analytical techniques such as scanning electron microscopy or scanning Auger microscopy (SAM). Special samples with multilayers which are perpendicular to their surface are presently proposed for testing the lateral resolution, as discussed in recent works of Senoner et al (2004 Surf. Interface Anal.
36 1423). The relevant experiment needs a theoretical description based on recent progress in the theory. Monte Carlo simulations of electron trajectories make possible an accurate description of the considered system. We selected exemplary samples, with layers perpendicular to the surface. The layer materials are elemental solids with high, medium and low atomic numbers, i.e. Au|Cu|Au and Au|Si|Au. For these systems calculations of the Auger current versus beam position were performed. We found that, for a system with layers consisting of elements of considerably different atomic numbers, the relation can have an unexpected extreme. This observation can be important in analysis of SAM pictures.
Charge localization in [1 1 2] Si/Ge and Ge/Si core–shell nanowires
Authors: Liu Nuo , Li Yan-Rong , Lu Ning , Yao Yong-Xin , Fang Xiao-Wei , Wang Cai-Zhuang , Ho Kai-Ming
Published: June 2010

We report a first-principles study of Ge/Si and Si/Ge core/shell nanowires (NWs) along the [1 1 2] direction with a diameter of ∼20 Å using density-functional theory. Our results show that for both NW structures the band gaps are indirect and are significantly larger than the gaps of the bulk crystalline Si and Ge. The quantum well confinement effect in these NWs is found to be modified by a type II lineup of band structures. Moreover, the carriers on the conduction band minimum are strongly localized in the Si region while the carriers on the valence band maximum are located mainly in the Ge region. The charge separation and localization characters make the NWs good candidates for nanochannels in field effect devices, solar cells with higher efficiency and high mobility heterostructures due to the spatial separation of one-dimensional electron gas and one-dimensional hole gas.
Inertial manifolds for reaction diffusion equations in higher space dimensions
Authors: Mallet-Paret John , Sell George R.
Published: June 2010

In this paper we show that the scalar reaction diffusion equation
\[

u
t

=
ν
Δ
u
+
f
(
x
,
u
)
,

u
∈
R

{u_t} = \nu \Delta u + f(x,u),\qquad u \in R

\]
with

x
∈

Ω
n

⊂

R
n

(
n
=
2
,
3
)

x \in {\Omega _n} \subset {R^n}\quad (n = 2,3)

and with Dirichlet, Neumann, or periodic boundary conditions, has an inertial manifold when (1) the equation is dissipative, and (2)

f
f

is of class

C
3

{C^3}

and for

Ω
3

=

(
0
,
2
π

)
3

{\Omega _3} = {(0,2\pi )^3}

or

Ω
2

=
(
0
,
2
π

/

a
1

)
×
(
0
,
2
π

/

a
2

)

{\Omega _2} = (0,2\pi /{a_1}) \times (0,2\pi /{a_2})

, where

a
1

{a_1}

and

a
2

{a_2}

are positive. The proof is based on an (abstract) Invariant Manifold Theorem for flows on a Hilbert space. It is significant that on

Ω
3

{\Omega _3}

the spectrum of the Laplacian

Δ
\Delta

does not have arbitrary large gaps, as required in other theories of inertial manifolds. Our proof is based on a crucial property of the Schroedinger operator

Δ
+
υ
(
x
)

\Delta + \upsilon (x)

, which is valid only in space dimension

n
≤
3

n \leq 3

. This property says that

Δ
+
υ
(
x
)

\Delta + \upsilon (x)

can be well approximated by the constant coefficient problem

Δ
+

υ
¯

\Delta + \bar \upsilon

over large segments of the Hilbert space

L
2

(
Ω
)

{L^2}(\Omega )

, where

υ
¯

=

(

vol

Ω

)

−
1

∫
Ω

υ

d
x

\bar \upsilon = {({\text {vol}}\Omega )^{ - 1}}\int _\Omega {\upsilon \;dx}

is the average value of

υ
\upsilon

. We call this property the Principle of Spatial Averaging. The proof that the Schroedinger operator satisfies the Principle of Spatial Averaging on the regions

Ω
2

{\Omega _2}

and

Ω
3

{\Omega _3}

described above follows from a gap theorem for finite families of quadratic forms, which we present in an Appendix to this paper.
Two-dimensional area minimizing integral currents are classical minimal surfaces
Authors: Chang Sheldon Xu-Dong
Published: June 2010

Geometric measure theory guarantees the existence of area minimizing integral currents spanning a given boundary or representing a given integral homology class on a compact Riemannian manifold. We study the regularity of such generalized surfaces. We prove that in case the dimension of the area minimizing integral currents is two, then they are classical minimal surfaces. Among the consequences of this regularity result, we know now that any two dimensional integral homology class on a compact Riemannian manifold can be represented by a finite integral linear combination of classical closed minimal surfaces that have only finitely many intersection points. The result is proved by using the theory of multiple-valued functions developed by F. Almgren in [A]. We extend many important estimates in his paper and extend his construction of center manifolds. We use the branched center manifolds and lowest order term in the multiple-valued functions approximating the area minimizing currents to construct two sequences of branched surfaces near an interior singular point to separate the nearby singularity gradually. The analysis developed in this paper enables us to conclude the generalized surface must coincide with one of the branched surfaces.
A partition property of simplices in Euclidean space
Authors: Frankl P. , Rödl V.
Published: June 2010

Given the vertex set

A
A

of a nondegenerate simplex in

R
d

{R^d}

, it is shown that for some positive

ε
=
ε
(
A
)

\varepsilon = \varepsilon (A)

and every partition of

R
n

{R^n}

into fewer than

(
1
+
ε

)
n

{(1 + \varepsilon )^n}

parts, one of the parts must contain a set congruent to

A
A

. This solves a fifteen-year-old problem of Erdös et al. [E].
The structure of rational and ruled symplectic 4-manifolds
Authors: McDuff Dusa
Published: June 2010

This paper investigates the structure of compact symplectic

4
4

-manifolds

(
V
,
ω
)

(V,\omega )

which contain a symplectically embedded copy

C
C

of

S
2

{S^2}

with nonnegative self-intersection number. Such a pair

(
V
,
C
,
ω
)

(V,C,\omega )

is called minimal if, in addition, the open manifold

V
−
C

V - C

contains no exceptional curves (i.e., symplectically embedded

2
2

-spheres with self-intersection -1). We show that every such pair

(
V
,
C
,
ω
)

(V,C,\omega )

covers a minimal pair

(

V
¯

,
C
,

ω
¯

)

(\overline V ,C,\overline \omega )

which may be obtained from

V
V

by blowing down a finite number of disjoint exceptional curves in

V
−
C

V - C

. Further, the family of manifold pairs

(
V
,
C
,
ω
)

(V,C,\omega )

under consideration is closed under blowing up and down. We next give a complete list of the possible minimal pairs. We show that

V
¯

\overline V

is symplectomorphic either to

C

P
2

\mathbb {C}{P^2}

with its standard form, or to an

S
2

{S^2}

-bundle over a compact surface with a symplectic structure which is uniquely determined by its cohomology class. Moreover, this symplectomorphism may be chosen so that it takes

C
C

either to a complex line or quadric in

C

P
2

\mathbb {C}{P^2}

, or, in the case when

V
¯

\overline V

is a bundle, to a fiber or section of the bundle.
A separator theorem for nonplanar graphs
Authors: Alon Noga , Seymour Paul , Thomas Robin
Published: June 2010

Let

G
G

be an

n
n

-vertex graph with no minor isomorphic to an

h
h

-vertex complete graph. We prove that the vertices of

G
G

can be partitioned into three sets

A
,

B
,

C

A,\;B,\;C

such that no edge joins a vertex in

A
A

with a vertex in

B
B

, neither

A
A

nor

B
B

contains more than

2
n

/

3

2n/3

vertices, and

C
C

contains no more than

h

3

/

2

n

1

/

2

{h^{3/2}}{n^{1/2}}

vertices. This extends a theorem of Lipton and Tarjan for planar graphs. We exhibit an algorithm which finds such a partition

(
A
,

B
,

C
)

(A,\;B,\;C)

in time

O
(

h

1

/

2

n

1

/

2

m
)

O({h^{1/2}}{n^{1/2}}m)

, where

m
=

|

V
(
G
)

|

+

|

E
(
G
)

|

m = \left | {V(G)} \right | + \left | {E(G)} \right |

.
Williams’s conjecture is false for reducible subshifts
Authors: Kim K. H. , Roush F. W.
Published: June 2010

We show that for two subshifts of finite type having exactly two irreducible components, strong shift equivalence is not the same as shift equivalence. This refutes the Williams conjecture

[

W

]

[{\text {W}}]

in the reducible case. The irreducible case remains an open problem.
Twistors, Kähler manifolds, and bimeromorphic geometry. II
Authors: LeBrun Claude , Poon Yat Sun
Published: June 2010

Using examples [13] of compact complex

3
3

-manifolds that arise as twistor spaces, we show that the class of compact complex manifolds bimeromorphic to Kähler manifolds is not stable under small deformations of complex structure.
The Closely Related RNA helicases, UAP56 and URH49, Preferentially Form Distinct mRNA Export Machineries and Coordinately Regulate Mitotic Progression
Authors: Yamazaki Tomohiro , Fujiwara Naoko , Yukinaga Hiroko , Ebisuya Miki , Shiki Takuya , Kurihara Tomoya , Kioka Noriyuki , Kambe Taiho , Nagao Masaya , Nishida Eisuke , Masuda Seiji
Published: June 2010

Nuclear export of mRNA is an essential process for eukaryotic gene expression. The TREX complex couples gene expression from transcription and splicing to mRNA export. Sub2, a core component of the TREX complex in yeast, has diversified in humans to two closely related RNA helicases, UAP56 and URH49. Here, we show that URH49 forms a novel URH49–CIP29 complex, termed the AREX (alternative mRNA export) complex, whereas UAP56 forms the human TREX complex. The mRNAs regulated by these helicases are different at the genome-wide level. The two sets of target mRNAs contain distinct subsets of key mitotic regulators. Consistent with their target mRNAs, depletion of UAP56 causes mitotic delay and sister chromatid cohesion defects, whereas depletion of URH49 causes chromosome arm resolution defects and failure of cytokinesis. In addition, depletion of the other human TREX components or CIP29 causes mitotic defects similar to those observed in UAP56- or URH49-depleted cells, respectively. Taken together, the two closely related RNA helicases have evolved to form distinct mRNA export machineries, which regulate mitosis at different steps.
Transgene Rescue Identifies an Essential Function forDrosophilaβ Spectrin in the Nervous System and a Selective Requirement for Ankyrin-2–binding Activity
Authors: Mazock G. Harper , Das Amlan , Base Christine , Dubreuil Ronald R.
Published: June 2010

The protein spectrin is ubiquitous in animal cells and is believed to play important roles in cell shape and membrane stability, cell polarity, and endomembrane traffic. Experiments here were undertaken to identify sites of essential β spectrin function in Drosophila and to determine whether spectrin and ankyrin function are strictly linked to one another. The Gal4-UAS system was used to drive tissue-specific overexpression of a β spectrin transgene or to knock down β spectrin expression with dsRNA. The results show that 1) overexpression of β spectrin in most of the cell types studied was lethal; 2) knockdown of β spectrin in most tissues had no detectable effect on growth or viability of the organism; and 3) nervous system-specific expression of a UAS-β spectrin transgene was sufficient to overcome the lethality of a loss-of-function β spectrin mutation. Thus β spectrin expression in other cells was not required for development of fertile adult males, although females lacking nonneuronal spectrin were sterile. Previous data indicated that binding of the DAnk1 isoform of ankyrin to spectrin was partially dispensable for viability. Domain swap experiments here uncovered a different requirement for neuronal DAnk2 binding to spectrin and establish that DAnk2-binding is critical for β spectrin function in vivo.
Regional Production Adjustment to Import Competition: Evidence from the French Agro‐Industry
Authors: Bagoulla Corinne , Chevassus-Lozza Emmanuelle , Daniel Karine , Gaigné Carl
Published: June 2010

This paper evaluates the impact of increasing imports on the reallocation of agrifood production across regions within countries. From French data for the period 1995–2002, we show that regional agrifood production adjusts differently to increasing imports according to the region where the agrifood firms are located. Even though proximity to consumers is important, an increase in agrifood imports does not increase agrifood production with a high demand but makes low‐wage regions more attractive. In addition, an increase in imports of agricultural products processed by agrifood firms leads to the reallocation of agrifood production away from regions with good agricultural access and toward those with limited access to agricultural products.
Brevity is not always a virtue in primate communication
Authors: Bezerra Bruna M. , Souto Antonio S. , Radford Andrew N. , Jones Gareth
Published: June 2010

Semple
et al
. (Semple
et al.
in press,
Biol. Lett.
(
doi:10.1098/rsbl.2009.1062
)) argued that the ‘law of brevity’ (an inverse relationship between word length and frequency of use) applies not only to human language but also to vocal signalling in non-human primates, because coding efficiency is paramount in both situations. We analysed the frequency of use of signals of different duration in the vocal repertoires of two Neotropical primate species studied in the wild—the common marmoset (
Callithrix jacchus
) and the golden-backed uakari (
Cacajao melanocephalus
). The key prediction of the law of brevity was not supported in either species: although the most frequently emitted calls were relatively brief, they were not the shortest signals in the repertoire. The costs and benefits associated with signals of different duration must be appreciated to understand properly their frequency of use. Although relatively brief vocal signals may be favoured by natural selection in order to minimize energetic costs, the very briefest signals may be ambiguous, contain reduced information or be difficult to detect or locate, and may therefore be selected against. Analogies between human language and vocal communication in animals can be misleading as a basis for understanding frequency of use, because coding efficiency is not the only factor of importance in animal communication, and the costs and benefits associated with different signal durations will vary in a species-specific manner.
Triangular buckling patterns of twisted inextensible strips
Authors: Korte A. P. , Starostin E. L. , van der Heijden G. H. M.
Published: June 2010

When twisting a strip of paper or acetate under high longitudinal tension, one observes, at some critical load, a buckling of the strip into a regular triangular pattern. Very similar triangular facets have recently been found in solutions to a new set of geometrically exact equations describing the equilibrium shape of thin inextensible elastic strips. Here, we formulate a modified boundary-value problem for these equations and construct post-buckling solutions in good agreement with the observed pattern in twisted strips. We also study the force–extension and moment–twist behaviour of these strips by varying the mode number
n
of triangular facets and find critical loads with jumps to higher modes.
Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels
Authors: Munk Peter , Hansen Michael M. , Maes Gregory E. , Nielsen Torkel G. , Castonguay Martin , Riemann Lasse , Sparholt Henrik , Als Thomas D. , Aarestrup Kim , Andersen Nikolaj G. , Bachler Mirjam
Published: June 2010

Anguillid freshwater eels show remarkable life histories. In the Atlantic, the European eel (Anguilla anguilla) and American eel (Anguilla rostrata) undertake extensive migrations to spawn in the oceanic Sargasso Sea, and subsequently the offspring drift to foraging areas in Europe and North America, first as leaf-like leptocephali larvae that later metamorphose into glass eels. Since recruitment of European and American glass eels has declined drastically during past decades, there is a strong demand for further understanding of the early, oceanic phase of their life cycle. Consequently, during a field expedition to the eel spawning sites in the Sargasso Sea, we carried out a wide range of dedicated bio-physical studies across areas of eel larval distribution. Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical–biological linkages in the life-cycle completion of Atlantic eels.
Sea turtle nesting distributions and oceanographic constraints on hatchling migration
Authors: Putman Nathan F. , Bane John M. , Lohmann Kenneth J.
Published: June 2010

Patterns of abundance across a species's reproductive range are influenced by ecological and environmental factors that affect the survival of offspring. For marine animals whose offspring must migrate long distances, natural selection may favour reproduction in areas near ocean currents that facilitate migratory movements. Similarly, selection may act against the use of potential reproductive areas from which offspring have difficulty emigrating. As a first step towards investigating this conceptual framework, we analysed loggerhead sea turtle (Caretta caretta) nest abundance along the southeastern US coast as a function of distance to the Gulf Stream System (GSS), the ocean current to which hatchlings in this region migrate. Results indicate that nest density increases as distance to the GSS decreases. Distance to the GSS can account for at least 90 per cent of spatial variation in regional nest density. Even at smaller spatial scales, where local beach conditions presumably exert strong effects, at least 38 per cent of the variance is explained by distance from the GSS. These findings suggest that proximity to favourable ocean currents strongly influences sea turtle nesting distributions. Similar factors may influence patterns of abundance across the reproductive ranges of diverse marine animals, such as penguins, eels, salmon and seals.
Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river
Authors: Pusey B. J. , Arthington A. H. , Stewart‐Koster B. , Kennard M. J. , Read M. G.
Published: June 2010

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra‐annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.