bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the conformational dependence of mass-metric tensor determinants in serial polymers with constraints
Authors: Patriciu Alexandru , Chirikjian Gregory S. , Pappu Rohit V.
Published: December 2004

It is well known that mass-metric tensor determinants det(Gs) influence the equilibrium statistics and the rates of conformational transitions for polymers with constrained bond lengths and bond angles. It is now standard practice to include a Fixman-style compensating potential of the form Uc(qs)∝(−kBT/2)ln[det(Gs)] as part of algorithms for torsional space molecular dynamics. This elegant strategy helps eliminate unwarranted biases that arise due to the imposition of holonomic constraints. However, the precise nature and extent of variation of det(Gs) and hence ln[det(Gs)] with chain conformation and chain length has never been quantified. This type of analysis is crucial for understanding the nature of the conformational bias that the introduction of a Fixman potential aims to eliminate. Additionally, a detailed analysis of the conformational dependence of det(Gs) will help resolve ambiguities regarding suggestions for incorporating terms related to det(Gs) in the design of move sets in torsional space Monte Carlo simulations. In this work, we present results from a systematic study of the variation of det(Gs) for a serial polymer with fixed bond lengths and bond angles as a function of chain conformation and chain length. This analysis requires an algorithm designed for rapid computation of det(Gs) which simultaneously allows for a physical/geometric interpretation of the conformational dependence of det(Gs). Consequently, we provide a detailed discussion of our adaptation of an O(n) algorithm from the robotics literature, which leads to simple recursion relations for direct evaluation of det(Gs). Our analysis of the conformational dependence of det(Gs) yields the following insights. (1) det(Gs) is maximized for spatial conformers and minimized for planar conformations. (2) Previous work suggests that it is logical to expect that the conformational dependence of det(Gs) becomes more pronounced with increase in chain length. Confirming this expectation, we provide systematic quantification of the nature of this dependency and show that the difference in det(Gs) between spatial and planar conformers, i.e., between the maxima and minima of det(Gs) grows systematically with chain length. Finally, we provide a brief discussion of implications of our analysis for the design of move sets in Monte Carlo simulations.
Towards benchmark second-order correlation energies for large atoms: Zn2+ revisited
Authors: Flores J. R. , Słupski R. , Jankowski K. , Malinowski P.
Published: December 2004

To provide very accurate reference results for the second-order Møller–Plesset (MP2) energy and its various components for Zn2+, which plays for 3d-electron systems a similar role as Ne for smaller atoms and molecules, we have performed extensive calculation by two completely different implementations of the MP2 method: the finite element method (FEM) and the variation-perturbation (VP) method. The FEM and VP calculations yield partial wave contributions up to lmax=45 and 12, respectively. Detailed comparison of all FEM and VP energy components for lmax=12 has disclosed an extraordinary similarity, which justifies using the present results as benchmarks. The present correlation energies are compared with other works. The dependability of an earlier version of FEM, already applied to very large closed-shell atoms, is confirmed. It has been found that for larger atoms the accuracy of the analytical Hartree–Fock results has an impact on the accuracy of the MP2 energies greater than for smaller atoms. Fields of applications of the present results in studies of various electron correlation effects in 3d-electron atoms and molecules are indicated.
Vibrational spectra from atomic fluctuations in dynamics simulations. II. Solvent-induced frequency fluctuations at femtosecond time resolution
Authors: Schmitz Matthias , Tavan Paul
Published: December 2004

The midinfrared (MIR) spectra of molecules in polar solvents exhibit inhomogeneously broadened bands whose spectral positions are shifted as compared to the gas phase. The shifts are caused by interactions with structured solvation shells and the broadenings by fluctuations of these interactions. The MIR spectra can be calculated from hybrid molecular dynamics (MD) simulations, which treat the solute molecule by density functional theory and the solvent by molecular mechanics by the so-called instantaneous normal mode analysis (INMA) or by Fourier transforming the time correlation function (FTTCF) of the molecular dipole moment. In Paper I of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12233 (2004)] we explored an alternative method based on generalized virial (GV) frequencies noting, however, that GV systematically underestimates frequencies. As shown by us these artifacts are caused by solvent-induced fluctuations of the (i) equilibrium geometry, (ii) force constants, and (iii) normal mode directions as well as by (iv) diagonal and (v) off-diagonal anharmonicities. Here we now show, by analyzing the time scales of fluctuations and sample MD trajectories of formaldehyde in the gas phase and in water, that all these sources of computational artifacts can be made visible by a Fourier analysis of the normal coordinates. Correspondingly, the error sources (i) and (iii)–(v) can be removed by bandpass filtering, as long as the spectral signatures of the respective effects are well separated from the fundamental band. Furthermore, the artifacts arising from effect (ii) can be strongly diminished by a time-resolved version of the GV approach (TF-GV). The TF-GV method then yields for each mode j a trajectory of the vibrational frequency ωj(t|τ) at a time resolution τ>τj, which is only limited by the corresponding oscillation time τj=2π/ωj and, thus, is in the femtosecond range. A correlation analysis of these trajectories clearly separates the librational motions from the conformational dynamics of the solvation shells and yields the inhomogeneously broadened MIR spectra, if the theory of motional narrowing is properly included. The MIR spectrum of formaldehyde in solution obtained by TF-GV agrees very well with the FTTCF result, if one applies the so-called “harmonic approximation” quantum correction factor and a temperature scaling to the FTTCF intensities. Also for INMA an excellent agreement is achieved if one disregards a slight INMA overestimate of linewidths.
Interplanar torsion in the S1←S electronic spectrum of jet cooled 1-phenylimidazole
Authors: Robertson Evan G. , Thompson Christopher D. , Morrison Richard J. S.
Published: December 2004

The S1←S0 transition of 1-phenylimidazole (1PI) has been studied in a supersonic jet expansion by resonant two-photon ionization. The origin band at 36 075 cm−1 is accompanied by a low frequency progression associated with torsion about the bond connecting phenyl and imidazole groups. Torsional potentials have been determined for both states. In S0, φmin=37.2±0.5° and the planar barrier is 339±20 cm−1, while in S1, φmin=17.6±0.5° and the planar barrier is 57±2 cm−1. The transition moment alignment is observed to be consistent with an excited state of Lb character, in spite of the “off-axis” conjugation provided by the imidazole ring. These results are compared with ab initio calculations on both states, performed using Hartree–Fock, Møller–Plesset second-order perturbation, density functional theory with the Becke3–Lee–Yang–Parr functional, time-dependant density functional theory, configuration interaction singles, and complete active space self-consistent field methods. Solution-phase UV spectra of neutral and protonated 1PI are also reported.
Effect of surfactant on the long-wave instability of a shear-imposed liquid flow down an inclined plane
Authors: Wei Hsien-Hung
Published: December 2004

The effect of an insoluble surfactant on the linear stability of a shear-imposed flow down an inclined plane is examined in the long-wavelength limit. It has been known that a free falling film flow with surfactant is stable to long-wavelength disturbances at sufficiently small Reynolds numbers. Imposing an additional interfacial shear, however, could cause instability due to the shear-induced Marangoni effect. Two modes of the stability are identified and the corresponding growth rates are derived. The underlying mechanisms of the stability are also elucidated in detail.
Drift kinetic equation exact through second order in gyroradius expansion
Authors: Simakov Andrei N. , Catto Peter J.
Published: December 2004

The drift kinetic equation of Hazeltine [R. D. Hazeltine, Plasma Phys. 15, 77 (1973)] for a magnetized plasma of arbitrary collisionality is widely believed to be exact through the second order in the gyroradius expansion. It is demonstrated that this equation is only exact through the first order. The reason is that when evaluating the second-order gyrophase dependent distribution function, Hazeltine neglected contributions from the first-order gyrophase dependent distribution function, and then used this incomplete expression to derive the equation for the gyrophase independent distribution function. Consequently, the second-order distribution function and the stress tensor derived by this approach are incomplete. By relaxing slightly Hazeltine’s orderings one is able to obtain a drift kinetic equation accurate through the second order in the gyroradius expansion. In addition, the gyroviscous stress tensor for plasmas of arbitrary collisionality is obtained.
Properties of defect modes in one-dimensional photonic crystals containing a defect layer with a negative refractive index
Authors: Xu Kun-yuan , Zheng Xiguang , She Wei-long
Published: December 2004

The band structures of one-dimensional photonic crystals containing a defect layer with a negative refractive index are studied, showing that the defect modes possess three types of dispersion: positive, zero, and negative types. The zero and negative dispersion phenomena may be useful in the design of large incident angle filters and narrow frequency and sharp angular filters, respectively. The dispersion multiplicity of the defect modes can be understood by an approximate formula. Moreover, the splitting of one defect mode into multiple defect modes is observed in the band gap when the parameters of the defect layer vary. This phase transition phenomenon may be useful in the design of multiple channeled filters or filters with a rectangular profile. The condition for the critical point of the phase transition is also analyzed.
One-electron versus electron–electron interaction contributions to the spin–spin coupling mechanism in nuclear magnetic resonance spectroscopy: Analysis of basic electronic effects
Authors: Gräfenstein Jürgen , Cremer Dieter
Published: December 2004

For the first time, the nuclear magnetic resonance (NMR) spin–spin coupling mechanism is decomposed into one-electron and electron–electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin–spin coupling constants result from totally different Fermi contact coupling mechanisms. J1(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas J2(H,H) spin–spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of J1(C,H) and J2(H,H), respectively, for hydrocarbons.
Wavepacket propagation using time-sliced semiclassical initial value methods
Authors: Wallace Brett B. , Reimers Jeffrey R.
Published: December 2004

A new semiclassical initial value representation (SC-IVR) propagator and a SC-IVR propagator originally introduced by Kay [J. Chem. Phys. 100, 4432 (1994)], are investigated for use in the split-operator method for solving the time-dependent Schrödinger equation. It is shown that the SC-IVR propagators can be derived from a procedure involving modified Filinov filtering of the Van Vleck expression for the semiclassical propagator. The two SC-IVR propagators have been selected for investigation because they avoid the need to perform a coherent state basis set expansion that is necessary in other time-slicing propagation schemes. An efficient scheme for solving the propagators is introduced and can be considered to be a semiclassical form of the effective propagators of Makri [Chem. Phys. Lett. 159, 489 (1989)]. Results from applications to a one-dimensional, two-dimensional, and three-dimensional Hamiltonian for a double-well potential are presented.
Water structure in nanopores of agarose gel by Raman spectroscopy
Authors: Ratajska-Gadomska Bożena , Gadomski Wojciech
Published: December 2004

The evolution of water structure during the gelation process is examined in aqueous solution of agarose using Raman spectroscopy of the O–H stretching band. The measurements have been performed at room temperature for different concentrations of agarose, which yields different dimensions of nanopores in the network of the created gel. Our results show that water confined in the gel pores exhibits evident changes in the local order of molecules in comparison with bulk water and water in the sol state. During the sol–gel transition the number of molecules that participate in the regular tetrahedral H-bond structure increases, and the effect is stronger for higher concentration of the biopolymer.
Mid-infrared second-order susceptibility of α-quartz and its application to visible-infrared surface sum-frequency spectroscopy
Authors: Hore Dennis K. , Hamamoto Mathew Y. , Richmond Geraldine L.
Published: December 2004

We provide the first account of the second-order susceptibility of quartz down to 10 μm (1000 cm−1) and show how this data may be used along with the sum-frequency response of an amorphous gold surface to elucidate the nonlinear susceptibility of any material in the mid-infrared region. Crystalline quartz is an established material for use in second-harmonic and sum-frequency generation studies of new systems, on account of its well-characterized linear and nonlinear optical properties. Previous knowledge of its nonlinear susceptibility has been limited to its transparent region, wavelengths shorter than about 3 μm. Longer wavelength χ(2) values for quartz are particularly important for techniques such as vibrational sum-frequency spectroscopy which are expanding into the mid-IR with the increasing availability of widely tunable infrared laser sources.
Two-dimensional hydration shells of alkali metal ions at a hydrophobic surface
Authors: Meng Sheng , Chakarov D. V. , Kasemo B. , Gao Shiwu
Published: December 2004

We study the hydration shell formation of alkali metal ions at a graphite surface. Two-dimensional shell structures are found in the initial stage of hydration, in contrast to the three-dimensional structures in bulk water and clusters. Comparison of vibrational spectra with experiments identifies the shell structures and the thermally induced transition from the first to the second shell. We also found intriguing competition between hydration and ion–surface interaction, leading to different solvation dynamics between K and Na. Implications of these results in ionic processes at interfaces are elaborated.
Electron self-injection and acceleration driven by a tightly focused intense laser beam in an underdense plasma
Authors: Xu Han , Yu Wei , Lu Peixiang , Senecha V. K. , He Feng , Shen Baifei , Qian Liejia , Li Ruxin , Xu Zhizhan
Published: December 2004

A scheme for electron self-injection in the laser wakefield acceleration is proposed. In this scheme, the transverse wave breaking of the wakefield and the tightly focused geometry of the laser beam play important roles. A large number of the background electrons are self-injected into the acceleration phase of the wakefield during the defocusing of the tightly focused laser beam as it propagates through an underdense plasma. Particle-in-cell simulations performed using a 2D3V code have shown generation of a collimated electron bunch with a total number of 1.4×109 and energies up to 8MeV.
Energy controlled insertion of polar molecules in dense fluids
Authors: De Fabritiis Gianni , Delgado-Buscalioni Rafael , Coveney Peter V.
Published: December 2004

We present a method to search low energy configurations of polar molecules in the complex potential energy surfaces associated with dense fluids. The search is done in the configurational space of the translational and rotational degrees of freedom of the molecule, combining steepest-descent and Newton–Raphson steps which embed information on the average sizes of the potential energy wells obtained from prior inspection of the liquid structure. We perform a molecular dynamics simulation of a liquid water shell which demonstrates that the method enables fast and energy-controlled water molecule insertion in aqueous environments. The algorithm finds low energy configurations of incoming water molecules around three orders of magnitude faster than direct random insertion. This method represents an important step towards dynamic simulations of open systems and it may also prove useful for energy-biased ensemble average calculations of the chemical potential.
Atomic composition effect on the ordering of solution-phase synthesized FePt nanoparticle films
Authors: Yu Andrew C. C. , Mizuno M. , Sasaki Y. , Kondo H.
Published: December 2004

FePt nanoparticle monolayer films were fabricated with the nanoparticles stabilized on organic-coupling-layer coated Si substrates. The as-prepared films were nonmagnetic. In order to transform the nanoparticle phase from chemically disordered face-centered-cubic to chemically ordered L10, the films were annealed at 800°C under nitrogen atmosphere for 30min. The annealed films showed different degrees of sintering depending on the organic coupling layer materials used. At room temperature, sintered films exhibited high coercivity up to 2.4×104Oe, while monodispersive films with insignificant sintering showed a low coercivity of 1.1×102Oe. Such results can be explained by a large atomic composition distribution among the nanoparticles together with the size effect on ordering. Improvement of the nanoparticle atomic composition homogeneity is essential for applying the nanoparticle films for future ultrahigh-density data storage applications.
dc Magnetoencephalography: Direct measurement in a magnetically extremely-well shielded room
Authors: Burghoff M. , Sander T. H. , Schnabel A. , Drung D. , Trahms L. , Curio G. , Mackert B.-M.
Published: December 2004

Direct measurement of slow brain activity in the range of seconds is reported. The measurements were made by superconducting quantum interference devices operating in a magnetically extremely well-shielded room. Directly measured dc magnetoencephalography (MEG) reveals that sustained fields of the brain rise with a sharp slope immediately after motor stimulation, whereas their relaxation to the resting level is slower and is delayed by several seconds. These features of sustained brain activity could not be resolved by modulated dc MEG which was applied earlier to study these phenomena.
Solvation states of HCl in mixed ether:acid crystals: A computational study
Authors: Buch V. , Mohamed F. , Krack Mathias , Sadlej J. , Devlin J. P. , Parrinello M.
Published: December 2004

Acid solvation states are investigated in the recently discovered mixed ether:acid crystalline solids. The solids are simulated using on-the-fly molecular dynamics as implemented in the density functional code QUICKSTEP employing Gaussian basis sets. The solids are shown to display a remarkably broad range of acid solvation states, depending on the ether:acid ratio, including proton sharing in the 1:1 case, proton transfer to the ether in 1:2, and perturbed molecular acid in 1:6. The observed variation of the infrared spectra with the composition is accounted for qualitatively with the help of the calculations.
Direct observations of dislocation half-loops inserted from the surface of the GeSi heteroepitaxial film
Authors: Bolkhovityanov Yu. B. , Deryabin A. S. , Gutakovskii A. K. , Revenko M. A. , Sokolov L. V.
Published: December 2004

The initial stage of relaxation of mechanical stresses in the Ge0.32Si0.68∕Si(001) heterostructure grown by low-temperature (300°C) molecular-beam epitaxy is studied by means of transmission electron microscopy. Dislocation half-loops propagating from the film surface and generating misfit dislocations during expansion are visualized.
Electron-beam-induced surface quasimelting of Co granular nanowires
Authors: Huh Seung H. , Nakajima Atsushi
Published: December 2004

Electron-beam-induced surface quasimelting of Co granular nanowires (GNWs) of 6–10nm in diameter and ∼30nm in length has been studied using a high-resolution electron microscope. From the time evolution of electron microscope images as a function of the irradiation time, it has been revealed that the morphological change in the Co GNW is quite different from that in a Co nanocluster (NC) in terms of structures and phase transitions. For example, the allotropic β→α transition, inhibited in the Co NC, can proceed in the Co GNW through the lattice softening of fcc (111) facets without dimensional collapse.
Effects of n-type 4H-SiC epitaxial wafer quality on reliability of thermal oxides
Authors: Senzaki Junji , Kojima Kazutoshi , Fukuda Kenji
Published: December 2004

The reliability of thermal oxides was investigated on n-type 4H-SiC(0001) epitaxial wafers with different metal impurity concentrations and surface roughness. Time-zero dielectric breakdown measurements showed that almost all of the thermal oxides ruptured at a field-to-breakdown (EBD) of 10MV∕cm, and that the maximum EBD was 11MV∕cm, despite the influence of the epitaxial wafer. On the other hand, time-dependent dielectric breakdown measurements indicated that the charge-to-breakdown (QBD) of the thermal oxides was influenced by the epitaxial wafer. This suggests that two types of oxide breakdown regimes exist under a high-stress field: one resulting from wafer influences, and the other intrinsic.
Detection and characterization of longitudinal field for tip-enhanced Raman spectroscopy
Authors: Hayazawa Norihiko , Saito Yuika , Kawata Satoshi
Published: December 2004

We characterized the longitudinal field formed at a tightly focused spot by a high numerical aperture objective lens using a tip-enhanced near-field microscope. The longitudinal field efficiently excites the localized surface plasmon polaritons at the metallic tip apex resulting in an electric field enhancement. Radially polarized light generated by a combination of four half-waveplates successfully increases the longitudinal field resulting in higher sensitivity for tip-enhanced Raman spectroscopy of adenine nanocrystals.
Current-induced electroresistive effect in mixed-phase La0.67Ca0.33MnO3 thin films
Authors: Masuno A. , Terashima T. , Shimakawa Y. , Takano M.
Published: December 2004

We examined electroresistive effects of epitaxial thin films of La0.67Ca0.33MnO3 deposited on LaAlO3(100) substrates. To be noted here is that these oxides are considerably lattice-mismatched. Measurements of the resistivity, magnetoresistance effect, and current-voltage characteristics of these films revealed that they were inhomogeneous and composed of domains of the highly strained charge-ordered insulator (COI) and the less strained ferromagnetic metal (FMM). By using a microfabricating process, we obtained high current densities and observed a current-induced irreversible behavior at low temperature. The irreversibility became larger with increasing current density. Below the insulator-metal (ferromagnetic) transition temperature, spin-polarized electrons in the FMM domains were injected into the neighboring COI domains. There they forced antiferromagnetically ordered spins to align parallel, leading to a current-induced first-order transition from the COI to the FMM.
Effect of the interfacial SiO2 layer thickness on the dominant carrier type in leakage currents through HfAlOx∕SiO2 gate dielectric films
Authors: Mizubayashi Wataru , Yasuda Naoki , Hisamatsu Hirokazu , Iwamoto Kunihiko , Tominaga Koji , Yamamoto Katsuhiko , Ota Hiroyuki , Horikawa Tsuyoshi , Nabatame Toshihide , Toriumi Akira
Published: December 2004

The carrier conduction mechanism of leakage current in n+-gate p-channel metal-insulator-semiconductor field-effect-transistors with HfAlOx (Hf:60at%,Al:40at%)∕SiO2 dielectric layers has been investigated using the carrier separation method. Since the gate current depends on the substrate voltage and both electron and hole currents are independent of temperature in the range of 25–150°C, the conduction mechanism for both currents is a tunneling process. It is shown that the dominant carrier in the leakage current depends on the structure of the high-k stack. When the interfacial SiO2 layer (IL) thickness increases at a fixed high-k thickness (Thigh-k), the dominant carrier in the leakage current changes from hole to electron at ∼2.0–2.3-nm-thick IL, because of asymmetric barrier height for electron and hole in the SiO2∕Si system. In contrast, for the case of a fixed IL thickness of 1.3nm, the hole current dominates in the leakage current, regardless of Thigh-k, due to symmetric barrier height of the conduction and valence bands in the HfAlOx∕Si system.
A simple approach to determine five thermomechanical properties of thin ductile films on an elastic substrate
Authors: Huang W. M. , Hu Y. Y. , An L.
Published: December 2004

We present a simple approach to determine five thermomechanical properties of linear strain hardening thin films, namely, the Young’s modulus, coefficient of thermal expansion, yield start stress, strain hardening, and Poisson’s ratio. The approach is based on the conventional curvature test on bilayer structures upon temperature variation. Three tests, which result in three curvature versus temperature curves, are enough to determine the values of these properties. Both the closed-form solutions and estimations are obtained.
Microsphere whispering-gallery-mode laser using HgTe quantum dots
Authors: Shopova S. I. , Farca G. , Rosenberger A. T. , Wickramanayake W. M. S. , Kotov N. A.
Published: December 2004

Ultralow-threshold continuous-wave lasing is achieved at room temperature in a fused-silica microsphere that is coated with HgTe quantum dots (colloidal nanoparticles). The 830nm pump input and HgTe microlaser output are efficiently coupled into and out of whispering-gallery modes by tapered fibers. Lasing occurs at wavelengths ranging from 1240 to 1780nm, depending on the size and composition of the quantum dots (HgCdTe is also used). A linear fit to the data determines the lowest observed threshold pump power to be 0±2μW.
Microstructural change near the martensitic transformation in a ferromagnetic shape memory alloy Ni51Fe22Ga27 studied by electron holography
Authors: Murakami Y. , Shindo D. , Oikawa K. , Kainuma R. , Ishida K.
Published: December 2004

Temperature dependence of the magnetic microstructure in a ferromagnetic shape memory alloy Ni51Fe22Ga27 has been studied by electron holography, by which the distribution of magnetic flux is clearly imaged. Although the magnetic flux is quite even in the parent phase near room temperature, it undergoes considerable modulation when the temperature approaches Ms (martensitic transformation start temperature). The magnetization distribution in the martensite appears to be inherited from that in the parent phase. The observations shed further light on the precursor phenomenon of martensitic transformations.
Tailoring the Ti∕4H–SiC Schottky barrier by ion irradiation
Authors: Roccaforte Fabrizio , Bongiorno Corrado , La Via Francesco , Raineri Vito
Published: December 2004

The effects of ion irradiation on the Ti∕4H–SiC Schottky barrier are discussed. The Ti∕SiC interfacial region was modified by irradiating Schottky diodes with 8 MeV Si+4 ions at fluences between 1×109 and 1×1012ions∕cm2. By increasing the ion fluence, an increase of the Schottky barrier ΦB occurs, from the value of 1.05 eV after preparation to the value of 1.21 eV after irradiation at a fluence of 1×1012ions∕cm2, without substantial changes in the ideality factor (n=1.09). Along with the barrier height increase, a decrease of the leakage current of about two orders of magnitude was observed after irradiation. The results were interpreted in terms of the structural and electrical modification of the interfacial region.
Correlated photon emission from a single II–VI quantum dot
Authors: Couteau C. , Moehl S. , Tinjod F. , Gérard J. M. , Kheng K. , Mariette H. , Gaj J. A. , Romestain R. , Poizat J. P.
Published: December 2004

We report correlation and cross-correlation measurements of photons emitted under continuous wave excitation by a single II–VI quantum dot (QD) grown by molecular-beam epitaxy. A standard technique of microphotoluminescence combined with an ultrafast photon correlation setup allowed us to see an antibunching effect on photons emitted by excitons recombining in a single CdTe∕ZnTe QD, as well as cross correlation within the biexciton (X2)-exciton (X) radiative cascade from the same dot. Fast microchannel plate photomultipliers and a time-correlated single photon module gave us an overall temporal resolution of 140ps better than the typical exciton lifetime in II–VI QDs of about 250ps.
Metal-coated carbon nanotube tips for magnetic force microscopy
Authors: Deng Zhifeng , Yenilmez Erhan , Leu Josh , Hoffman J. E. , Straver Eric W. J. , Dai Hongjie , Moler Kathryn A.
Published: December 2004

We fabricated cantilevers for magnetic force microscopy with carbon nanotube tips coated with magnetic material. Images of a custom hard drive demonstrated 20 nm lateral resolution, with prospects for further improvements.
Messenger RNA expression patterns in bovine embryos derived from in vitro procedures and their implications for development
Authors: Wrenzycki Christine , Herrmann Doris , Lucas-Hahn Andrea , Korsawe Karin , Lemme Erika , Niemann Heiner
Published: December 2004

The preimplantation bovine embryo is initially under the control of maternal genomic information that is accumulated during oogenesis. The genetic programme of development soon becomes dependent on new transcripts derived from activation of the embryonic genome. The early steps in development, including the timing of the first cleavage, activation of the embryonic genome, compaction and blastocyst formation, can be affected by the culture media and conditions, as well as the production procedure itself. These perturbations can possibly result in a marked decrease in the quality of the resulting blastocysts and may even affect the viability of offspring born after transfer. In vitro procedures such as in vitro production and somatic nuclear transfer of bovine embryos have been shown to be correlated with significant up- or downregulation, de novo induction or silencing of genes critical for undisturbed fetal and neonatal development. These alterations are likely to be caused by epigenetic modifications, such as DNA methylation and histone modifications. Analysis of perturbed epigenetic reprogramming and of the related phenomena, such as genomic imprinting and X-chromosome inactivation, in bovine embryos is promising for understanding the underlying mechanisms of developmental abnormalities, such as large offspring syndrome.
From fibroblasts and stem cells: implications for cell therapies and somatic cloning
Authors: Kues Wilfried A. , Carnwath Joseph W. , Niemann Heiner
Published: December 2004

Pluripotent embryonic stem cells (ESCs) from the inner cell mass of early murine and human embryos exhibit extensive self-renewal in culture and maintain their ability to differentiate into all cell lineages. These features make ESCs a suitable candidate for cell-replacement therapy. However, the use of early embryos has provoked considerable public debate based on ethical considerations. From this standpoint, stem cells derived from adult tissues are a more easily accepted alternative. Recent results suggest that adult stem cells have a broader range of potency than imagined initially. Although some claims have been called into question by the discovery that fusion between the stem cells and differentiated cells can occur spontaneously, in other cases somatic stem cells have been induced to commit to various lineages by the extra- or intracellular environment. Recent data from our laboratory suggest that changes in culture conditions can expand a subpopulation of cells with a pluripotent phenotype from primary fibroblast cultures. The present paper critically reviews recent data on the potency of somatic stem cells, methods to modify the potency of somatic cells and implications for cell-based therapies.
126 EFFECTS OF THE REPRODUCTIVE STATUS ON DEVELOPMENTAL COMPETENCE OF RECIPIENT OOCYTES AFTER SOMATIC CELL NUCLEAR TRANSFER IN CAT
Authors: Otoi T. , Karja N.W.K. , Fahrudin M. , Agung B. , Wongsrikeao P.
Published: December 2004

The reproductive status of donor cat has been suggested to influence developmental competence of the oocytes after IVM/IVF (Karja et al. 2002 Theriogenology 57, 2289–2298). This study was conducted to examine the effect of the reproductive cycle stage of cat ovaries supplying recipient oocytes for nuclear transfer (NT) on the developmental competence of the oocytes after somatic cell nuclear transfer. Cat ovaries were collected at local veterinary clinics and stored at 35°C for a short period (1–6 h). Based on the presence or absence of follicles and corpora lutea, the ovarian pairs collected were classified into the inactive, follicular or luteal stages. Cumulus-oocyte complexes (COCs) were obtained from ovaries at each stage of the reproductive cycle by mincing/dissection and matured in vitro for 24 h, as previously described (Karja et al. 2002 Theriogenology 57, 2289–2298). In vitro matured oocytes from ovaries at the inactive (n = 114), follicular (n = 124), and luteal (n = 126) stages were mechanically enucleated in PBS supplemented with 5 μL mL−1 of cytochalasin B and 3 mg mL−1 BSA, and reconstructed with fibroblast cells derived from uterus tissue. The couplets were fused in Zimmerman medium with a single DC pulse of 1.5 kV cm−1 for 50 μs. The successfully fused couplets were activated by a 5-min exposure to 10 μg mL−1 calcium ionophore A23187 in MK1 medium (Kanda et al. 1998 J. Vet. Med. Sci. 60, 423–431) followed by 5 h of incubation in MK1 medium supplemented with 10 μg mL−1 cycloheximide. The NT embryos were cultured in MK1 medium supplemented with 4 mg mL−1 BSA at 38.0°C in a humidified atmosphere of 5% CO2 in air. At 72 h of culture, all cleaved NT embryos were transferred to fresh MK1 medium supplemented with 5% fetal calf serum for an additional 4 days to evaluate their ability of development to the blastocyst stage. Data were analyzed by ANOVA. There were no significant differences (P > 0.05) among the fused oocytes derived from ovaries at the inactive, follicular, and luteal stages with respect to the percentages of cleavage (64.4%, 69.4%, and 74.5%, respectively) and blastocyst formation (17.4%, 21.0%, and 12.0%, respectively). These results indicate that the reproductive cycle stage of cat ovaries has no apparent effect on the development at competence of recipient oocytes after somatic cell nuclear transfer.
135 REGULATION OF GLUCOSE METABOLISM TO DECREASE LIPID CONTENT OF IN VIRTO-PRODUCED BOVINE EMBRYOS
Authors: De La Torre-Sanchez J. , Gardner D. , Preis K. , Seidel Jr G.
Published: December 2004

Our objective was to improve normality of embryos produced in vitro with regulators of carbohydrate metabolism at doses optimized in earlier experiments. Eight- to 16-cell embryos were produced in vitro in the G1/G2 system (chemically defined sequential medium with recombinant human serum albumin), and then cultured 3 days in G2 containing metabolic regulators as follows: phenazine ethosulfate (PES), 0.3 μM; NaN3, 27 μM; 2,4-dinitrophenol (DNP), 30 μM; and control. The following responses were analyzed by ANOVA in 2 to 4 replicates of 8–12 embryos each: glucose uptake and metabolism (uptake measured by microfluorometry of medium after incubating an embryo 3 h; metabolism measured as 3H2O released after incubating an embryo 3 h in medium containing 5-3H glucose), % of glucose metabolized via the pentose phosphate pathway (PPP rate), lactate production, glycolysis (% of lactate produced from glucose taken up on a molar basis), lipid accumulation (number of >2 μM Sudan Black B positive granules/103 μm2), % live Day 14 embryos recovered from embryos transferred to recipients at Day 7, and average surface area of embryos collected. In vivo-derived embryos were included as a second control for lipid evaluation. PES-treated embryos had higher glucose metabolism (P < 0.05) and lower glucose uptake (P < 0.01) than embryos in NaN3 and tended to have a higher PPP rate (P < 0.11) than controls; however, glycolysis was higher for PES than other treatments (P < 0.01) (Table 1). Lipid accumulation of embryos from PES was markedly lower than any other in vitro treatments (P < 0.01), but higher than in vivo embryos (3.31 ± 2.78 lipid granules) (P < 0.01). NaN3- and DNP-treated embryos both accumulated lipid similar to in vitro controls. No treatment differences were found in developmental competence when Day 7 embryos were transferred to recipients and recovered 1 week later (43 to 54% live embryos recovered), nor were there any significant differences (P > 0.1) in surface area. Embryos exposed to PES at the compaction and post-compaction stages accumulated much less lipid than controls or embryos exposed to other metabolic regulators, making this a very promising treatment. PES oxidizes NADPH; the molecular mechanism of PES appears to involve increased flux of glucose through the PPP while decreasing availability of NADPH for fatty acid synthesis.

Table 1.
Response of embryos to metabolic regulators
154 EFFECTS OF BLASTOMERE BIOPSY AND OXYGEN CONCENTRATION DURING CULTURE ON THE DEVELOPMENT AND INTERFERON-TAU SECRETION OF BOVINE EMBRYOS
Authors: Johnson K.M. , Alvarez X. , Kubisch H.M.
Published: December 2004

Pre-implantation genetic diagnosis has become a powerful tool in human in vitro fertilization. Yet, for ethical reasons, controlled experiments assessing the effects of embryo biopsies on human embryos are difficult to perform. Therefore, a series of experiments was performed to examine the effects of blastomere biopsies on subsequent development of IVF-derived bovine embryos cultured under either atmospheric or low (5%) oxygen. Embryos were generated by IVF of in vitro-matured oocytes and cultured in CR1aa medium containing 5% bovine fetal serum. The first experiment was designed to assess the optimal time for blastomere removal. One blastomere was removed from each of a large number of embryos at either 48 or 72 h after IVF. Biopsy at 48 h resulted in 17.2% (10/58) of embryos proceeding to the blastocyst stage, which was significantly lower than when biopsies were performed at 72 h (37.5% (33/88), P < 0.05). In the second experiment, embryos were cultured under either atmospheric or 5% O2 following blastomere removal. Biopsies at 72 h had no effect on rate of blastocyst formation with 38.5% (110/286) of controls and 33.7% (60/178) of biopsied embryos proceeding to the blastocyst stage. However, culture under 5% O2 significantly increased the number of blastocysts from 29.9% (69/231) to 43.3% (101/233). This effect was significant in both biopsied and control embryos. In contrast, staining of blastocysts for cell numbers did not reveal any effects of biopsies or culture conditions. In the final experiment, biopsies were again performed at 72 h and embryos were cultured as previously. Blastocysts were collected and cultured individually for 48 h in 50-μL-medium droplets in their respective O2 concentrations after which time the medium was assayed for concentration of interferon-tau (IFN-τ). Previous work has shown that IFN-τ secretion can be affected by genetic and environmental factors. Reduced O2 concentration again significantly increased blastocyst formation from 24.9 to 36.9% (49/197 vs. 75/203, P < 0.05), while blastomere removal had no effect on development. IFN-τ secretion did not differ between biopsied and control blastocysts, although culture under atmospheric O2 resulted in significantly increased IFN-τ concentration in medium droplets (12,690.1 ± 2715.6 vs. 4726.8 ± 2488.5 pM, P < 0.05).
This work was supported by a grant (HMK) from the National Institutes of Health (HD 36421).
159 TWIN vs. SINGLE TRANSFER OF IVP HOLSTEIN HEIFER EMBRYOS TO BEEF RECIPIENTS
Authors: Fischer-Brown A. , Barquero G. , Clark S. , Ferguson C. , Ireland F. , Jensen N. , Lane S. , Lindsey B. , Lopes P. , Monson R. , Northey D. , Reeder A. , Rutledge J. , Wheeler M. , Kesler D.
Published: December 2004

Use of sexed semen in conjunction with in vitro embryo production is a potentially efficient means of obtaining offspring of predetermined sex. Here we evaluate a production scheme involving single and bilateral twin transfer of Holstein female embryos to beef cattle recipients. Holstein oocytes were fertilized with the X-bearing fraction of gender-sorted Holstein semen. Cumulus cells were removed with aid of a vortex or microfluidic device (μFD). Half of the vortexed embryos were cultured in KSOMaaBSA (control), as were all μFD embryos. The remaining vortexed embryos were cultured in control medium with 6% avian white yolk (WY). Embryo production and transfer occurred across five replicates. Cows (n = 475) were synchronized using an Ovsynch protocol. They were administered GnRH on Day −9, PGF on Day −2, and GnRH on Day 0. Half of the cows received a CIDR (1.38 g progesterone) with the 1st GnRH injection. The CIDR was removed at the time of PGF treatment. Day 7 Grade 1 blastocysts were transferred fresh 7 days after the 2nd GnRH injection. Control and WY embryos were transferred as ipsilateral singles and bilateral twins; μFD embryos were transferred singly. Pregnancy was diagnosed with ultrasound between 41–46 days and confirmed between 60–90 days; fetal sexing confirmed that 95% of fetuses were female. Effects on embryo survival were analyzed by logistic regression. Chi-square analysis was applied to survival rates. Replication affected embryo survival (P < 0.05). There was no effect of cumulus removal, medium, or CIDR use. Fetal loss between ultrasounds was greater for twin vs. single transfers (30% vs. 15%, respectively; P < 0.01). Probability of embryo survival was estimated to increase ∼0.006 with each increasing day postpartum. Five cases of hydrallantois were detected during the 5th month of gestation for 1 control twin, 1 WY single, and 3 WY twin transfers, originating from 3 replicates. On a production per transfer basis, the proportion of fetuses obtained for single and twin transfers was 30% and 55%, respectively (P < 0.001). Although there was greater embryonic loss for twin compared to single transfers, a higher percentage of cows receiving twins established and maintained pregnancy. Large-scale transfer of IVP Holstein heifer embryos to beef recipients is a feasible production scheme.

Table 1.
Embryo survival and pregnancy rates
16 A CIDR-BASED TIMED AI PROTOCOL RESULTED IN A HIGHLY ACCEPTABLE THERAPEUTIC OUTCOME ON OVARIAN FOLLICULAR CYSTS IN LACTATING DAIRY COWS
Authors: Kim I.H. , Kim U.H. , Nam H.W.
Published: December 2004

Ovarian follicular cysts are a major reproductive failure in lactating dairy cows, prolonging the calving-to-conception interval and resulting in great economic loss. Treatment with GnRH is currently the most common therapy used for ovarian follicular cysts in dairy cows, but definitive results remain inconclusive. Recently, the Ovsynch protocol has been introduced as a therapeutic strategy for ovarian cysts in dairy cows (Bartolome et al. 2000 Theriogenology 53, 815–825). The objective of the present study was to evaluate the therapeutic effect of a CIDR-based timed AI (TAI) protocol on ovarian follicular cysts in lactating Holstein cows. Lactating Holstein cows with ovarian follicular cysts were randomly assigned to two treatments: (1) insertion of a CIDR intravaginal progesterone device (CIDR™, InterAg, Hamilton, New Zealand) with an injection of 100 μg GnRH (Conceral®, Dongbang Co., Seoul, Korea) on Day 0, an injection of PGF2α (Lutalyse®, Pharmacia & Upjohn, Puurs, Belgium) and removal of the device on Day 7, an injection of GnRH on Day 9, and TAI 16 h after the GnRH injection (CIDR+GnRH-PGF2α-GnRH group, n = 30); and (2) an injection of 100 μg GnRH on Day 0, and AI at estrus (AIE) within 2 months after treatment with GnRH (GnRH group, n = 72). Day 0 was the day of initiation of the experiment. Pregnancy diagnosis was determined at 60 days after AI using both ultrasonography and rectal palpation. Pregnancy rates between groups were compared by chi-square analysis. Treatment-to-conception interval for cows that conceived by 150 days post-treatment was compared by Student's t-test. The pregnancy rate after TAI following the CIDR+GnRH-PGF2α-GnRH protocol (46.7%) was higher (P < 0.05) than that after AIE following GnRH injection (25.0%). The treatment-to-conception interval (mean ± SEM) was shorter (P < 0.01) in the CIDR+GnRH-PGF2α-GnRH group (46 ± 12 days) than in the GnRH group (88 ± 10 days), representing 21.9% more cows being pregnant by 150 days after treatment. These results indicate that the CIDR-based TAI protocol can be used as an efficient therapeutic tool for ovarian follicular cysts in lactating dairy cows. Follicular dynamics and endocrine changes during the CIDR+GnRH-PGF2α-GnRH protocol is being determined to clarify the beneficial outcome in this study.
This work was supported by a Chungbuk National University Grant in 2004.