bluuebunny/crossref_metadata_2025 huggingface dataset:
Vaccines for cervical cancer
Authors: LOWNDES C. M.
Published: January 2006

This review focuses on current and future prevention of invasive cervical cancer (ICC), the second most common cancer among women worldwide. Implementation of population-based cytological screening programmes, using the ‘Pap’ smear to detect pre-cancerous lesions in the cervix, has resulted in substantial declines in mortality and morbidity from ICC in North America and some European countries. However, cases of, and deaths from, ICC continue to occur. Primary prevention of infection with high-risk human papillomavirus (HPV) types, the central causal factor of ICC, could further reduce incidence of and mortality from ICC. This is particularly the case in developing countries, which bear 80% of the burden of ICC, and where effective Pap screening programmes are extremely difficult to implement. Very promising results from several trials of synthetic HPV type-specific monovalent (HPV 16) and bivalent (HPV 16 and 18) vaccines have recently been published, showing high efficacy against type-specific persistent HPV infection and development of type-specific pre-cancerous lesions. Large-scale phase III trials of a number of such vaccine candidates are currently underway, and there is real hope that an effective vaccine capable of protecting against infection with HPV types 16 and 18 (which together account for ∼70% of cervical cancer cases worldwide), and thereby of preventing development of a very significant proportion of cases of ICC, could be available within the next 2 years.
Estimated PDFs of climate system properties including natural and anthropogenic forcings
Authors: Forest Chris E. , Stone Peter H. , Sokolov Andrei P.
Published: January 2006

We present revised probability density functions (PDF) for climate system properties (climate sensitivity, rate of deep‐ocean heat uptake, and the net aerosol forcing strength) that include the effect on 20th century temperature changes of natural as well as anthropogenic forcings. The additional natural forcings, primarily the cooling by volcanic eruptions, affect the PDF by requiring a higher climate sensitivity and a lower rate of deep‐ocean heat uptake to reproduce the observed temperature changes. The estimated 90% range of climate sensitivity is 2.1 to 8.9 K. The net aerosol forcing strength for the 1980s shifted toward positive values to compensate for the volcanic forcing with 90% bounds of −0.74 to −0.14 W/m2. The rate of deep‐ocean heat uptake is reduced with the effective diffusivity, Kv, ranging from 0.05 to 4.1 cm2/s. This upper bound implies that many AOGCMs mix heat into the deep ocean (below the mixed layer) too efficiently.
Determination of post‐perovskite phase transition boundary in MgSiO3 using Au and MgO pressure standards
Authors: Hirose Kei , Sinmyo Ryosuke , Sata Nagayoshi , Ohishi Yasuo
Published: January 2006

We have determined the post‐perovskite phase transition boundary in MgSiO3 by in‐situ X‐ray diffraction measurements, using Au and MgO as internal pressure standards. Results demonstrate that phase transition occurs at 113 GPa and 2400 K with a positive Clapeyron slope of +4.7 MPa/K, based on the Au pressure scale. On the other hand, the simultaneous measurements of MgO standard show that the phase boundary is located at 119 GPa and 2400 K with a Clapeyron slope of +11.5 MPa/K, consistently with the previous experimental results based on the Pt scale and the theoretical calculations. Our experiments also indicate that the stabilities of perovskite and post‐perovskite in all of (Mg0.89Fe0.11)2SiO4, natural pyrolitic mantle, and MORB compositions are consistent with the phase transition boundary in pure MgSiO3, when all the data are compared using the same Au scale. The compositional variations in natural systems have little effect on the post‐perovskite phase transition.
Fluid induced seismicity guided by a continental fault: Injection experiment of 2004/2005 at the German Deep Drilling Site (KTB)
Authors: Shapiro S. A. , Kummerow J. , Dinske C. , Asch G. , Rothert E. , Erzinger J. , Kümpel H.‐J. , Kind R.
Published: January 2006

Recent hydraulic experiments at the KTB site have shown that seismicity induced by long‐term fluid injection directly into a continental crustal fault remains guided by this fault. The seismicity is triggered by pressure perturbations as low as 0.01–1 bars at the hypocenters. A combination of sequential one‐year fluid extraction (2002/2003) and one‐year fluid injection (2004/2005) experiments has shown that only positive pore pressure perturbation (i.e., injections) was able to induce the seismicity. Moreover, the onset of seismicity roughly coincides with the time of compensation of the extracted fluid volume by the following injection. This confirms that the pressure diffusion is a dominant mechanism of seismicity triggering by fluid injections. The probed fault shows a significant anisotropy and non‐linearity of its hydraulic behaviour. Its hydraulic diffusivity is up to one order of magnitude larger than that of surrounding rocks.
Effect of topographic curvature on near‐surface stresses and application to sheeting joints
Authors: Martel Stephen J.
Published: January 2006

Sheeting joints have attracted attention for more than two centuries, yet their cause has remained unclear. Sheeting joints are opening mode rock fractures that form subparallel to the topographic surface and develop to depths of at least 100 m. They are best developed beneath convex surfaces in massive rocks where the compressive stress parallel to the surface (P) is high. A tensile stress normal to a convex traction‐free surface will arise if the product of P and the surface curvature (k) exceeds the product of the unit weight of rock (ρg) and the cosine of the slope (cosβ). The tensile stress contributes fundamentally to sheeting joints; erosion of overburden, by itself, does not. Rocks with high uniaxial compressive strengths host sheeting joints because they can sustain the high compressive stresses necessary to generate surface‐normal tensile stresses given typical curvatures in landscapes.
A cellular automaton for the factor of safety field in landslides modeling
Authors: Piegari E. , Cataudella V. , Di Maio R. , Milano L. , Nicodemi M.
Published: January 2006

Landslide inventories show that the statistical distribution of the area of recorded events is well described by a power law over a range of decades. To understand these distributions, we consider a cellular automaton model based on a dissipative dynamical variable associated to a time and position dependent factor of safety. The model is able to reproduce the complex structure of landslide distribution, as experimentally reported. In particular, we investigate the role of the rate of change of the system dynamical variables, induced by an external drive, on landslide modeling and its implications on hazard assessment. As the rate is increased, the model has a crossover from a critical regime with power‐laws to non power‐law behaviors. We suggest that the detection of patterns of correlated domains in monitored regions can be crucial to identify the response of the system to perturbations, i.e., for hazard assessment.
A statistical comparison of solar wind sources of moderate and intense geomagnetic storms at solar minimum and maximum
Authors: Zhang Jichun , Liemohn Michael W. , Kozyra Janet U. , Thomsen Michelle F. , Elliott Heather A. , Weygand James M.
Published: January 2006

Superposed epoch analyses of 549 storms are performed to make a comparison of solar wind features of geomagnetic storm events at solar minimum (July 1974 to June 1977; July 1984 to June 1987; July 1994 to June 1997) and solar maximum (January 1979 to December 1981; January 1989 to December 1991; July 1999 to June 2002). In this study, geomagnetic storms are defined by the pressure‐corrected Dst (Dst*) and classified into moderate storms (−100 nT < Dst* ≤ −50 nT) and intense storms (Dst* ≤ −100 nT). The average values of interplanetary magnetic field (IMF), solar wind plasma, NOAA/POES hemispheric power, Kp, and Dst* are analyzed and compared among the different storm categories. During the main phase of storms in each category, the average solar wind plasma parameters and IMF components are disturbed and compressed by a relative high‐speed plasma stream. It is shown that the peak of the average solar wind density leads the minimum Dst* (the zero epoch time) by 4.3–7.0 hours, which is longer than the peak time difference (0.3–1.0 hour) between the average IMF Bs and Dst*min. For intense storms at solar minimum, the average IMF By is greatly disturbed during both the main phase and the recovery phase. In addition, the average solar wind density is enhanced up to 28 cm−3, but the average solar wind bulk flow in this storm category is lower than those in all other categories. A significant finding is that the average interplanetary causes of intense storms at solar minimum are found to be against the well‐known empirical criteria (Bs ≥ 10 nT or VBs ≥ 5.0 mV/m for ≥3 hours), having a long interval of average Bs = ∼10 nT with dual peaks separated by ∼4.0 hours. The interplanetary and solar origins of storms in the different storm categories are also discussed.
Long‐lived geomagnetic storms and coronal mass ejections
Authors: Xie H. , Gopalswamy N. , Manoharan P. K. , Lara A. , Yashiro S. , Lepri S.
Published: January 2006

Coronal mass ejections (CMEs) are major solar events that are known to cause large geomagnetic storms (Dst< −100 nT). Isolated geomagnetic storms typically have a main phase of 3–12 hours and a recovery phase of around 1 day. However, there are some storms with main and recovery phases exceeding ∼3 days. We trace the origin of these long‐lived geomagnetic storms (LLGMS) to frontside halo CMEs. We studied 37 LLGMS events withDst< −100 nT and the associated CMEs which occurred during 1998–2002. It is found that LLGMS events are caused by (1) successive CMEs, accounting for ∼64.9% (24 of 37); (2) single CMEs, accounting for ∼21.6% (8 of 37); and (3) high‐speed streams (HSS) in corotating interaction regions (CIRs) with no related CME, accounting for ∼13.5% (5 of 37). The long duration of the LLGMS events was found to be due to successive CMEs and HSS events; the high intensity of the LLGMS events was related to the interaction of CMEs with other CMEs and HSS events. We find that the duration of LLGMS is well correlated to the number of participating CMEs (correlation coefficientr= 0.78). We also find that the intensity of LLGMS has a good correlation with the degree of interaction (the number of CMEs interacting with a HSS event or with themselves) (r= 0.67). The role of preconditioning in LLGMS events, where theDstdevelopment occurred in multiple steps in the main and recovery phases, has been investigated. It is found that preconditioning does not affect the main phase of the LLGMS events, while it plays an important role during the recovery phase of the LLGMS events.
Paleomagnetic and geochronological study of the Halaqiaola basalts, southern margin of the Altai Mountains, northern Xinjiang: Constraints on neotectonic convergent patterns north of Tibet
Authors: Huang Baochun , Piper John D. A. , He Huaiyu , Zhang Chunxia , Zhu Rixiang
Published: January 2006

A combined geochronological and paleomagnetic study is reported from Miocene basalts from Halaqiaola and Paleocene to Eocene red beds from Fuyun at the southern Altai Mountains, northern Xinjiang. Three new 40Ar/39Ar ages determined by fresh matrix from the Halaqiaola basalts collectively confirm the presence of Cenozoic magmatic activity in the northern Xinjiang. Alternating field and thermal demagnetization identify stable characteristic remanences with single reversed polarity in the basalts and red beds. Rock magnetic analysis identifies pseudosingle‐domain titanomagnetites as carriers of remanence in the basalts. Paleomagnetic results from the Fuyun red beds indicate that inclination shallowing is present in this rock facies as also found in previous red bed studies from central Asia. In contrast, the time‐averaged paleomagnetic direction from the basalts shows that no paleomagnetically discernible northward convergence has occurred north of Junggar since early Miocene times. Analysis of available Cretaceous and Cenozoic paleomagnetic data from volcanic rocks in central Asia shows that Neogene and Quaternary paleolatitudes are statistically concordant with predicted values from Eurasian references, suggesting that no significant northward convergence has occurred north of Tibet during the last 20 Myr. Cretaceous and Paleogene paleolatitudes lie ∼5–6 ± 7° south of predicted values from the Eurasian path and suggest that neotectonic convergence of the order of several hundred kilometers has occurred north of the southwest Tian Shan. It is possible that neotectonic northward convergence north of Tibet will prove to be paleomagnetically undetectable, but more data are required to confirm this.
Implications of deformation following the 2002 Denali, Alaska, earthquake for postseismic relaxation processes and lithospheric rheology
Authors: Freed Andrew M. , Bürgmann Roland , Calais Eric , Freymueller Jeff , Hreinsdóttir Sigrún
Published: January 2006

During the first 2 years following the 2002 Mw = 7.9 Denali, Alaska, strike‐slip earthquake, a large array of Global Positioning System (GPS) receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm/yr in the near field. Here we use three‐dimensional (3‐D) viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations. We consider afterslip both from an inversion of GPS displacements and from stress‐driven forward models, poroelastic rebound, and viscoelastic flow in the lower crust and upper mantle. Several conclusions can be drawn: (1) No single mechanism can explain the postseismic observations. (2) Significant postseismic flow below a depth of 60 km is required to explain observed far‐field motions, best explained by a weak upper mantle with a depth‐dependent effective viscosity that ranges from >1019 Pa s at the Moho (50 km depth) to 3–4 × 1018 Pa s at 100 km depth. (3) Shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip. (4) There is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress‐driven slip. Afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth, though our modeling does not favor either mechanism. If the process is viscoelastic relaxation, the viscosity is a factor of 3 greater than the inferred mantle viscosity. (5) Poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the Denali/Totschunda junction. These conclusions lead us to infer an Alaskan mechanical lithosphere that is about 60 km thick, overlying a weak asthenosphere, and a Denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top ∼20 km and time‐dependent aseismic shear below.
Effect of ammonia on new particle formation: A kinetic H2SO4‐H2O‐NH3 nucleation model constrained by laboratory measurements
Authors: Yu Fangqun
Published: January 2006

A clear understanding of the nucleation mechanisms is important to understand the lifecycle of atmospheric particles and to provide reliable predictions of climate change associated with aerosols. On the basis of the classical ternary homogeneous nucleation (THN) theory developed in recent years, the presence of ppt level NH3 concentration significantly enhances nucleation rates. Here we compare the predicted NH3 enhancement with that derived from several reported experiments. We find that the differences between results predicted and observed are very large. Compared to the binary homogeneous nucleation of H2SO4‐H2O (no NH3), the classical THN theory predicts up to ∼30 orders of magnitude enhancement in the nucleation rates in the presence of ppt level NH3, while the laboratory measurements show only one to two orders of magnitude enhancement in the presence of several ppt to several ppm level of NH3. Furthermore, the classical THN theory predicts a decrease in nucleation rates as RH increases, but the measurements indicate an opposite trend. Since experimental results are probably more reliable than the theoretical model, we developed a kinetic THN model so that the nucleation enhancement effect of NH3 derived from these experimental results could be included. The kinetic model assumes that H2SO4 is the principal specie dominating the cluster growth and nucleation, while H2O and NH3 are secondary species influencing the cluster compositions and hence the evaporation coefficient of H2SO4 from the clusters. The kinetic model is a new approach to simulating THN, and it can take into account the thermodynamic data of molecular clusters derived from density functional theory study and prenucleation cluster measurements. The preliminary simulations using the kinetic THN model constrained by the experimental results indicate a negligible contribution of THN to new particle formation in the boundary atmosphere. Our analysis suggests that the kinetic THN model is unlikely to underpredict the real ternary nucleation rates by much as long as there is no significant error in the experimental results. The implication of this finding and areas for further investigations are discussed.
Construction of a 10‐min‐gridded precipitation data set for the Greater Alpine Region for 1800–2003
Authors: Efthymiadis Dimitrios , Jones Philip D. , Briffa Keith R. , Auer Ingeborg , Böhm Reinhard , Schöner Wolfgang , Frei Christoph , Schmidli Jürg
Published: January 2006

A new precipitation data set for the Greater Alpine Region (GAR; 4°E–19°E, 43°N–49°N) has been developed. It provides monthly precipitation totals, for the 1800–2003 period, gridded at 10‐min resolution. The new HISTALP 10‐min‐grid data set is based on 192 long‐term homogenized precipitation series from meteorological stations across the study domain and a high‐resolution precipitation climatology for the 1971–1990 period. The effective coverage of the data set depends on the observations available in the station network which progressively declines back to the early 19th century (from 192 to 5 stations). To aid the use of these data in other studies, an accompanying data set has also been developed, which provides a measure of the quality of each monthly precipitation estimate over the grid: the explained variance, relative to the 1931–2000 (maximum data availability) period. The computed quality score illustrates the comparatively poorer accuracy of the data set for regions and months with less coherent precipitation fields (i.e., over the Alps and in summer) and when the number of stations is reduced, particularly before 1840. The derived gridded field has also been compared for the whole and geographical subregions with other independently developed data sets and is found to provide a similar description of the precipitation in the GAR for places and periods of common coverage. The data set is publicly available athttp://www.cru.uea.ac.uk/.
Dissipative dynamics of laser induced nonadiabatic molecular alignment
Authors: Ramakrishna S. , Seideman Tamar
Published: January 2006

Nonadiabatic alignment induced by short, moderately intense laser pulses in molecules coupled to dissipative environments is studied within a nonperturbative density matrix theory. We focus primarily on exploring and extending a recently proposed approach [Phys. Rev. Lett. 95, 113001 (2005)], wherein nonadiabatic laser alignment is used as a coherence spectroscopy that probes the dissipative properties of the solvent. To that end we apply the method to several molecular collision systems that exhibit sufficiently varied behavior to represent a broad variety of chemical environments. These include molecules in low temperature gas jets, in room temperature gas cells, and in dense liquids. We examine also the possibility of prolonging the duration of the field free (post-pulse) alignment in dissipative media by a proper choice of the system parameters.
Construction of environment states in quantum-chemical density-matrix renormalization group calculations
Authors: Moritz Gerrit , Reiher Markus
Published: January 2006

The application of the quantum-chemical density-matrix renormalization group (DMRG) algorithm is cumbersome for complex electronic structures with many active orbitals. The high computational cost is mainly due to the poor convergence of standard DMRG calculations. A factor which affects the convergence behavior of the calculations is the choice of the start-up procedure. In this start-up step matrix representations of operators have to be calculated in a guessed many-electron basis of the DMRG environment block. Different possibilities for the construction of these basis states exist, and we first compare four procedures to approximate the environment states using Slater determinants explicitly. These start-up procedures are applied to DMRG calculations on a sophisticated test system: the chromium dimer. It is found that the converged energies and the rate of convergence depend significantly on the choice of the start-up procedure. However, since already the most simple start-up procedure, which uses only the Hartree-Fock determinant, is comparatively good, Slater determinants, in general, appear not to be a good choice as approximate environment basis states for convergence acceleration. Based on extensive test calculations it is demonstrated that the computational cost can be significantly reduced if the number of total states m is successively increased. This is done in such a way that the environment states are built up stepwise from system states of previous truncated DMRG sweeps for slowly increasing m values.
Correlation induced insulator to metal transition: A systematic density functional study on highly doped n-type trans-polyacetylene
Authors: Sen Sabyasachi , Chakrabarti Swapan
Published: January 2006

Since its discovery in 1977, a number of quantum chemical calculations have been attempted to simulate the metallic state of highly doped trans-polyacetylene. These simulations have focused on the possible closure of the band gap at high doping level due to a charge-induced elimination of Peierls distortion; however, conclusive demonstration of a metallic state has not been achieved. The present study presents density functional theory calculations of the band structure of highly doped trans-polyacetylene with explicit inclusion of the metal atoms in a one-dimensional periodic structure. The results indicate (i) small lattice dimerization, i.e., remnant of Peierls distortion exists even in the heavily doped trans-polyacetylene sample, (ii) charge induced closure of the Peierls gap is not a necessary condition to arrive at a metallic state in such systems, and (iii) electronic correlation, as described at the density functional theory level, with a charge induced small Peierls distortion is sufficient to achieve metallic state of highly doped n-type trans-polyacetylene even in one dimension. Furthermore, comparison of functionals that include differing degrees of electron correlation suggest that correlation promotes formation of the metallic state.
Recombination of photodissociated iodine: A time-resolved x-ray-diffraction study
Authors: Wulff M. , Bratos S. , Plech A. , Vuilleumier R. , Mirloup F. , Lorenc M. , Kong Q. , Ihee H.
Published: January 2006

A time-resolved x-ray-diffraction experiment is presented that aims to study the recombination of laser-dissociated iodine molecules dissolved in CCl4. This process is monitored over an extended time interval from pico- to microseconds. The variations of atom-atom distances are probed with a milliangstrom resolution. A recent theory of time-resolved x-ray diffraction is used to analyze the experimental data; it employs the correlation function approach of statistical mechanics. The most striking outcome of this study is the experimental determination of time-dependent I–I atom-atom distribution functions. The structure of the CCl4 solvent changes simultaneously; the solvent thus appears as a reaction partner rather than an inert medium hosting it. Thermal expansion of the system is nonuniform in time, an effect due to the presence of the acoustic horizon. One concludes that a time-resolved x-ray diffraction permits real-time visualization of solvent and solute motions during a chemical reaction.
Surface anchoring of rodlike molecules on corrugated substrates
Authors: Kiyohara Kenji , Asaka Kinji , Monobe Hirosato , Terasawa Naohiro , Shimizu Yo
Published: January 2006

We studied the mechanism of surface anchoring of rodlike molecules on substrates with the surfaces corrugated at molecular scale by molecular-dynamics simulation. We constructed a model for substrates that can have anisotoropic topographical patterns such as corrugation. The structural and thermodynamic properties of rodlike molecules on the corrugated surfaces, including the elastic and anchoring properties, were calculated and the influence of the surface structure on the anchoring was discussed. We found that the rodlike molecules are aligned along the grooves of the corrugated surfaces guided by the anisotropic molecular interaction between the molecules and the corrugated surface. The strength of anchoring was found to be increased when the period of corrugation is decreased at molecular level.
Compatible Lie brackets related to elliptic curve
Authors: Odesskii A. V. , Sokolov V. V.
Published: January 2006

For the direct sum of several copies of sln, a family of Lie brackets compatible with the initial one is constructed. The structure constants of these brackets are expressed in terms of θ functions associated with an elliptic curve. The structure of Casimir elements for these brackets is investigated. A generalization of this construction to the case of vector-valued θ-functions is presented. A different procedure for constructing compatible Lie brackets based on the argument shift method for quadratic Poisson brackets is discussed.
Doppler effect in fluorine K-Auger line produced in electron-induced core ionization of SF6
Authors: Mondal S. , Singh R. K. , Shanker R.
Published: January 2006

An experimental evidence is reported on the observation of the Doppler effect in fluorine K-Auger line emitted from a core-ionized SF6 molecule under an impact of 16keV electrons. The emitting source of the Auger line is found to acquire a kinetic energy of 4.7±0.3keV. We propose that such large energy is released from the Coulomb repulsion taking place between F+ and SF5+ fragment ions under influence of an intense focusing field of the incident electrons. In the presence of the Coulomb field of these ions, the Auger line obtains a polarization P=76%±7%.
Scalar field theory at finite temperature in D=2+1
Authors: Añaños G. N. J.
Published: January 2006

We discuss the φ6 theory defined in D=2+1-dimensional space-time and assume that the system is in equilibrium with a thermal bath at temperature β−1. We use the 1∕N expansion and the method of the composite operator (Cornwall, Jackiw, and Tomboulis) for summing a large set of Feynman graphs. We demonstrate explicitly the Coleman-Mermin-Wagner theorem at finite temperature.
Single rolled-up SiGe∕Si microtubes: Structure and thermal stability
Authors: Songmuang R. , Jin-Phillipp N. Y. , Mendach S. , Schmidt O. G.
Published: January 2006

We investigate the structure and thermal stability of freestanding SiGe∕Si rolled-up microtubes by secondary ion mass spectroscopy, scanning and transmission electron microscopy, as well as micro-Raman spectroscopy. The tube walls show good crystal quality but become thinner during tube fabrication, leading to smaller diameters than expected. Si–Si vibration modes from the wall are consistent with Raman shifts induced by the strain distribution in the structure. Furthermore, the Raman shifts are used to monitor the tube temperature during laser annealing. At high temperatures, the tube structure irreversibly changes due to Si and Ge interdiffusion and, most remarkably, by Ge condensation.
Coupling between lysozyme and trehalose dynamics: Microscopic insights from molecular-dynamics simulations
Authors: Dirama Taner E. , Curtis Joseph E. , Carri Gustavo A. , Sokolov Alexei P.
Published: January 2006

We have carried out molecular-dynamics simulations on fully flexible all-atom models of the protein lysozyme immersed in trehalose, an effective biopreservative, with the purpose of exploring the nature and extent of the dynamical coupling between them. Our study shows a strong coupling over a wide range of temperatures. We found that the onset of anharmonic behavior was dictated by changes in the dynamics and relaxation processes in the trehalose glass. The physical origin of protein-trehalose coupling was traced to the hydrogen bonds formed at the interface between the protein and the solvent. Moreover, protein-solvent hydrogen bonding was found to control the structural relaxation of the protein. The dynamics of the protein was found to be heterogeneous; the motions of surface and core atoms had different dependencies on temperature and, in addition, the surface atoms were more sensitive to the dynamics of the solvent than the core atoms. From the solvent perspective we found that the dynamics near the protein surface showed an unexpected enhanced mobility compared to the bulk. These results shed some light on the microscopic origins of the dynamical coupling in protein-solvent systems.
Calculation of the force between surfaces coated with grafted molecules by molecular simulation
Authors: Duque Daniel , Vega Lourdes F.
Published: January 2006

We discuss the calculation of the force between surfaces coated with anchored molecules. This force is related to the pressure and can therefore be calculated by the usual means: either by summing over all surface-particle forces or from the virial. However, we argue that the grafting of the molecule must be included by means of a restraining potential—otherwise, nonphysical results can be obtained, such as the appearance of a net force even when the particles are spaced very far away. Bond-stretching potentials are also required if the virial is employed.
Is Poisson-Boltzmann theory insufficient for protein folding simulations?
Authors: Lwin Thu Zar , Zhou Ruhong , Luo Ray
Published: January 2006

The Poisson-Boltzmann theory has been widely used in the studies of energetics and conformations of biological macromolecules. Recently, introduction of the efficient generalized Born approximation has greatly extended its applicability to areas such as protein folding simulations where highly efficient computation is crucial. However, limitations have been found in the folding simulations of a well-studied beta hairpin with several generalized Born implementations and different force fields. These studies have raised the question whether the underlining Poisson-Boltzmann theory, on which the generalized Born model is calibrated, is adequate in the treatment of polar interactions for the challenging protein folding simulations. To address the question whether the Poisson-Boltzmann theory in the current formalism might be insufficient, we directly tested our efficient numerical Poisson-Boltzmann implementation in the beta-hairpin folding simulation. Good agreement between simulation and experiment was found for the beta-hairpin equilibrium structures when the numerical Poisson-Boltzmann solvent and a recently improved generalized Born solvent were used. In addition simulated thermodynamic properties also agree well with experiment in both solvents. Finally, an overall agreement on the beta-hairpin folding mechanism was found between the current and previous studies. Thus, our simulations indicate that previously observed limitations are most likely due to imperfect calibration in previous generalized Born models but not due to the limitation of the Poisson-Boltzmann theory.
Finite-size scaling analysis on the phase transition of a ferromagnetic polymer chain model
Authors: Luo Meng-Bo
Published: January 2006

The finite-size scaling analysis method is applied to study the phase transition of a self-avoiding walking polymer chain with spatial nearest-neighbor ferromagnetic Ising interaction on the simple cubic lattice. Assuming the scaling M2(T,n)=n−2β∕ν[Φ0+Φ1n1∕ν(T−Tc)+O(n2∕ν(T−Tc)2)] with the square magnetization M2 as the order parameter and the chain length n as the size, we estimate the second-order phase-transition temperature Tc=1.784J∕kB and critical exponents 2β∕ν≈0.668 and ν≈1.0. The self-diffusion constant and the chain dimensions ⟨R2⟩ and ⟨S2⟩ do not obey such a scaling law.
Nanotube manipulation with focused ion beam
Authors: Deng Zhifeng , Yenilmez Erhan , Reilein Amy , Leu Joshua , Dai Hongjie , Moler Kathryn A.
Published: January 2006

We demonstrate the ability to straighten and align metal-coated carbon nanotubes with a focused ion beam. The metal-coated nanotubes align toward the source of the ion beam allowing their orientation to be changed at precise angles. By this technique, metal-coated nanotube tips that are several micrometers in length are prepared for scanning probe microscopy. We image high-aspect-ratio structures on the surface of a cell using these tips.
Formation of (111) nanotwin lamellae hillocks in polycrystalline silicon thin films caused by deposition of silicon dioxide layer
Authors: Imai Shigeki , Fujimoto Masayuki
Published: January 2006

Plasma-enhanced chemical vapor deposition was used to deposit layers of tetraethylorthosilicate at different temperatures. In the case of low-temperature deposition (300°C), the deposited film surface was smooth and the major surface defects of the polycrystalline silicon (poly-silicon) film surface were grooves of grain boundaries. In contrast, in the case of high-temperature deposition (500°C), the deposited silicon oxide surface exhibited hillocks, and these hillocks were derived from the top end of inclined silicon (111) where protruding nanotwin lamellae penetrated the poly-silicon thin film. The observed hillocks stemming from nanotwin lamellae could have been formed by compressive stress during high-temperature silicon dioxide deposition.
Cross-sectional imaging of sharp Si interlayers embedded in gallium arsenide
Authors: Duan Xiangmei , Baroni Stefano , Modesti Silvio , Peressi Maria
Published: January 2006

We investigate the electronic properties of the (110) cross-sectional surface of Si-doped GaAs using first-principles techniques. We focus on doping configurations with an equal concentration of Si impurities in cationic and anionic sites, such as occurring in a self-compensating doping regime. In particular we study a bilayer of Si atoms uniformly distributed over two consecutive (001) atomic layers. The simulated cross-sectional scanning tunneling microscopy images show a bright signal at negative bias, which is strongly attenuated when the bias is reversed. This scenario is consistent with experimental results which had been attributed to hitherto unidentified Si complexes.
Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles
Authors: Yang X. H. , Jaiser F. , Klinger S. , Neher D.
Published: January 2006

We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at ∼40wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd∕A and 8.8 lm∕W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component.
Influence of the nanoscale structure of gold thin films upon peroxidase-induced chemiluminescence
Authors: Lu Guowei , Cheng Bolin , Shen Hong , Chen Zhenghao , Yang Guozhen , Marquette Christophe A. , Blum Loic Jean , Tillement Olivier , Roux Stéphane , Ledoux Gilles , Descamps Armel , Perriat Pascal
Published: January 2006

Gold thin films with different nanoscaled roughness were elaborated by a pulsed-laser deposition technique in order to evaluate their ability to form biochip substrates. The crystal structure, microstructure, and optical absorption were investigated by x-ray diffraction, atomic force microscopy, and ultraviolet-visible absorption spectrum. Controlling the temperature of the substrate during the deposition process allows us to obtain samples with different roughness and grain sizes. The temperature can then be adjusted to elaborate thin films, which have either the optical behavior of bulk metal or that of individual clusters. This optical behavior strongly influences the chemiluminescence at 425nm of luminol brought to the vicinity of peroxidase supported by biomolecules physi- or chemisorbed on the films. In particular, the signal intensity increases of almost one order of magnitude when the film presents a significant surface resonance plasmon.
On the elastic constants of the zeolite chlorosodalite
Authors: Williams Jennifer J. , Evans Kenneth E. , Walton Richard I.
Published: January 2006

The use of force-field based molecular modeling to predict the elastic constants of the zeolite chlorosodalite is described. Theoretical predictions of the on-axis and off-axis elastic constants strongly suggest that an error exists in the published elastic constants of the material. When the previous experimental data are corrected by transposing the published directional ultrasound velocities, excellent agreement is observed between the off-axis plots of sodalite produced by experiment and modeling. Further confirmation of the prediction is supplied by considering the Zener ratios of other inorganic materials that possess cubic symmetry.
Microstructural and magnetic properties of zinc-blende MnAs films with half metallic characteristics grown on GaAs (100) substrates
Authors: Kim Tae Whan , Jeon Hee Chang , Kang Tae Won , Lee Ho Seong , Lee Jeong Yong , Jin Sungho
Published: January 2006

Zinc-blende structured MnAs epiaxial films with half metallic characteristics were grown on GaAs (100) substrates. The formation of the zinc-blende structured MnAs on GaAs was made possible via introduction of a strained yet epirelated InAs intermediate layer, the thickness of which was found critical for enabling the half metallic structure. The magnetization curves as functions of the magnetic fields showed magnetic hysteresis and isotropic ferromagnetic properties. The magnetoresistance behavior at various temperatures indicates that the MnAs thin film is half-metallic in nature.
Insights into electroluminescent emission from AlGaN∕GaN field effect transistors using micro-Raman thermal analysis
Authors: Pomeroy J. W. , Kuball M. , Uren M. J. , Hilton K. P. , Balmer R. S. , Martin T.
Published: January 2006

We present an analysis of AlGaN∕GaN heterostructure field effect transistor’s electric field and current distributions by electroluminescent emission and micro-Raman thermal analysis techniques. Raman and electroluminescence are complementary since they probe lattice and electron energy distributions, respectively. Electroluminescent (EL) emission and Joule self-heating are normally confined close to the drain edge of the gate in the high field region. But in some nonideal devices, the EL and self-heating peak are shifted towards the drain. There is evidence for an inhomogeneous current distribution and possibly nonradiative energy dissipation.
Development of the Theory of Helical Spin Ordering
Authors: Nagamiya T.
Published: January 2006

Theory of helical spin ordering in a lattice having one magnetic atom per unit cell and its extension to the case of several atoms per unit cell have brought about deeper understanding of magnetic structures than before. These theories are reformulated concisely in the present paper and their applications to Cr2O3-Fe2O3 solid solutions, MnP, Mn3Sn (spiraling triangular spins), and spinels are discussed. The role of uniaxial anisotropy energy in spin ordering and a particular spin order of an integral period of seven layers in thulium, as well as the pairing of spins in holmium due to sixfold anisotropy energy, are discussed. Transition between a fan structure and the parallel alignment in magnetic field and its example in MnP are mentioned. Finally, the existence of a spin-wave mode of zero frequency in a general modified-helical spin arrangement is pointed out.
Interpretation of the Magnetic Properties of the Rare Earth Chromites and the Rare Earth Manganites
Authors: Aleonard R. , Pauthenet R. , Rebouillat J. P. , Veyret C.
Published: January 2006

The magnetostatic properties of the rare earth chromites, RCrO3, and those of the rare earth manganites, RMnO3, have been studied between 1.6° and 1500°K, in fields up to 28 000 Oe. These compounds are antiferromagnetic; they present two Néel points.

For the rare earth chromites, the first Néel point varies between 112°K for LuCrO3 and 282°K for LaCrO3; it corresponds to the ordering of the spins of the Cr3+ ions; below this transition temperature, a ferromagnetism is superimposed upon the antiferromagnetism. The second Néel point is situated in the neighborhood of the temperature of liquid helium; it corresponds to the ordering of the moments of the rare earth ions.

These properties are interpreted in terms of a molecular-field model. The lattice of the Cr3+ ions and that of the R3+ ions are decomposed into two identical sublattices. The Cr-Cr exchange interaction is negative; it is dominant; it defines principally the first Néel point. The R-R interaction is negative and weaker; it defines the second Néel point. The R-Cr interaction can be positive or negative, and its magnitude is small. The configuration of the moments of the chromium ions can be weakly ferromagnetic; this would induce a ferromagnetic polarization of the rare earth ion, and can give rise to a compensation temperature.

With the perovskite rare earth manganites, the first Néel point is between 45°K for EuMnO3 and approximatively 131°K for LaMnO3; a ferromagnetism is superimposed upon the antiferromagnetism. These substances behave like the rare earth chromites.

With the hexagonal rare earth manganites, the first Néel point is characterized only by a change in the slope of the susceptibility curve; there is no superimposed ferromagnetism. Near 10°K, it appears a ferromagnetic term which can be induced by the ordering of the spins of the rare earth ions. The rare earth-manganese interaction is determined in the molecular-field approximation.

The interpretation of the magnetic properties of the rare earth chromites has been published in the “Compt. Rend, 262, 799, 866 (1966); a full report on the interpretation of the magnetic properties of the rare earth maganites will be published in “J. Phys.”.
Spin-Wave Interactions in a Heisenberg Ferromagnet
Authors: Marshall W. , Murray G.
Published: January 2006

The theory of spin-wave interactions is discussed using the double-time temperature-dependent Green's function technique. It is shown how the important parts of the third-order Green's functions can be deduced rigorously. By neglecting the remaining parts of these third-order functions it is then possible to obtain closed expressions for the first-order Green's functions and the spin correlation functions. One further approximation, which however is rigorous in the two limits S = 12 and S = ∞, is used. In agreement with Dyson's spin-wave theory it is found that ‘kinematic’ interactions produce no effects on the magnetization at low temperatures. However, it is shown that the kinematic interactions do affect the neutron cross sections for creation or annihalation of spin waves and the transverse magnetic susceptibility, and therefore, may be observed directly.
Spin Waves in 3d Metals
Authors: Shirane G. , Minkiewicz V. J. , Nathans R.
Published: January 2006

A review is given of recent measurements of spin-wave dispersion relations of the 3d metals by the Brookhaven neutron diffraction group using the diffraction technique and triple-axis spectrometry. The parameters D and β in the relation ħω = Dq2(1 − βq2) have been determined at 295°K for Fe, Co, Ni, and some of their alloys. These values are compared with those obtained by thin-film resonance and small-angle scattering.

The most extensive measurements were carried out on Fe using a triple-axis spectrometer. The dispersion relation was measured along the three principal symmetry directions for wavevectors up to q/qmax = 0.4. The stiffness constant D as well as the linewidth of selected spin waves were studied for the temperature range between 77°K and the Curie temperature, 1042°K. Well-defined magnons were observed up to a reduced temperature T/TC = 0.995, but not above TC.
Spin Waves in Sodium and Potassium
Authors: Dunifer Gerald , Schultz Sheldon , Schmidt Paul H.
Published: January 2006

The observation of spin-wave excitations originating in the conduction electrons of sodium and potassium metal is presented. The qualitative behavior of these spin-wave signals is given along with a detailed comparison of the experimental data with the theory (of spin waves) as derived by Platzman and Wolff. It is shown that with the aid of the theory, it is possible to extract information from the data which leads to the first two Legendre coefficients of the spin part of the Landau correlation function for a Fermi liquid. A discussion is given on how present uncertainties in these two coefficients can be substantially reduced in future work.
Localized vs Collective Descriptions of Magnetic Electrons
Authors: Goodenough John B.
Published: January 2006

Spontaneous band magnetism occurs as a transitional electron state, in the thermodynamic sense, between a localized-electron (or small-polaron) state and a conventional collective-electron state. The localized-electron state is well described by crystal-field theory, together with superexchange and double-exchange theories. Conventional band theory neglects electron correlations, except in the superconducting state. In the transitional state, electron correlations introduce not only the exchange interactions responsible for spontaneous magnetism, but also a deep minimum, if not an energy gap, in the density-of-states vs energy for half-filled bands. Since Umklapp processes stabilize antiferromagnetic vs ferromagnetic order as the Fermi surface approaches a Brillouin-zone boundary, it is possible to construct a semiempirical phase diagram for various electronic states in the space nd, b, T, where nd is the number of electrons per d orbital per atom, b is the transfer energy, and T is the temperature. Magnetic data that illustrate a few significant features of this diagram are discussed briefly, and it is pointed out that spontaneous band magnetism is a relatively rare phenomenon because the transitional state occurs over only a small range of b.
Magnetism in High Magnetic Fields
Authors: Foner Simon
Published: January 2006

A brief summary of several recent high-field studies of magnetism in solids at the National Magnet Laboratory is presented. Topics include high field superconductors, magnetic phase transitions in simple antiferromagnets, capabilities of high field Mössbauer measurements for microscopic studies of magnetic structures, rare earth metals, collective electron ferromagnetism, and dilute alloys.