bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal fluctuations in the mass of the Amazon River system and Earth's elastic response
Authors: Bevis Michael , Alsdorf Douglas , Kendrick Eric , Fortes Luiz Paulo , Forsberg Bruce , Smalley Robert , Becker Janet
Published: August 2005

A GPS station in Manaus, near the center of the Amazon basin, manifests an annual cycle of vertical displacement with a peak‐to‐peak amplitude of 50–75 mm. This is by far the largest crustal oscillation observed to date, and nearly 2–3 times larger than the amplitude predicted for this region. Vertical ground displacement is strongly anti‐correlated with the local stage height of the Amazon river, with no detectable time lag between the two time series. This suggests that we are observing, for the first time, a purely elastic response to changes in the weight of a flowing river system. We use a simple hydrological model to relate stage height to the regional pattern of flooding, and argue that the elastic oscillations observed in Manaus are dominated by changes in water loading developed within ∼200 km of the GPS station.
Mid‐Holocene NAO: A PMIP2 model intercomparison
Authors: Gladstone R. M. , Ross I. , Valdes P. J. , Abe‐Ouchi A. , Braconnot P. , Brewer S. , Kageyama M. , Kitoh A. , Legrande A. , Marti O. , Ohgaito R. , Otto‐Bliesner B. , Peltier W. R. , Vettoretti G.
Published: August 2005

The mid‐Holocene (6000 years before present) North Atlantic Oscillation (NAO) from nine models in the Paleoclimate Modeling Intercomparison Project Phase 2 is studied, primarily through principal component analysis of winter time North Atlantic sea level pressure (SLP). Modeled mid‐Holocene NAO and mean SLP show small changes compared to pre‐industrial control runs, with a shift in mean state towards a more positive NAO regime for three of the models. Modeled NAO variability shows little change, with a small increase for some models in the fraction of time spent in the NAO‐negative phase during the mid‐Holocene. Proxy based reconstructions of the NAO indicate a more positive NAO regime compared to present day during the mid‐ Holocene. We hypothesise that there was a small NAO+ like shift in mean state during the mid‐Holocene.
Observed and predicted responses of plant growth to climate across Canada
Authors: Bunn Andrew G. , Goetz Scott J. , Fiske Gregory J.
Published: August 2005

Using satellite observations from 1981–2000, and data interpolated from surface weather stations, we examined the association between gross photosynthetic activity (Pg) and climate across the boreal forest and tundra of Canada. The response of annual and interannual Pg was tightly coupled to climate, and seasonal associations between Pg and climate varied with plant functional types. The most important variable for modeling summer growth of conifer forests was the previous spring minimum temperature, whereas tundra responded primarily to summer maximum temperature. Using general circulation model predictors to 2050, we project that tundra will continue to grow vigorously in the coming decades while conifer forests will not. Increased tundra productivity will likely be associated with changes in vegetation composition (e.g., woody proliferation). If these biotic responses are stationary and persist as predicted, terrestrial carbon budgets will need to be modified.
Effects of internal rheology and surface cooling on the emplacement of lava flows
Authors: Lyman A. W. , Kerr R. C. , Griffiths R. W.
Published: August 2005

The emplacement dynamics of lava flows is modeled using a combination of laboratory experiments and theoretical scaling analyses for the case where a fixed volume of lava is rapidly released and spreads as a horizontal, two‐dimensional flow. We focus on the processes that determine the final runout length of the lava, including the growth of a crust due to surface cooling and the presence of an internal yield strength. We show that solidifying flows with no internal yield strength first spread in slumping and viscous flow regimes, before a final regime where the yield strength of the growing crust stops the flow. We then demonstrate that solidifying flows with an internal yield strength can be stopped by either the internal yield strength or the growing crust. We also find that the yield strength of the solidified crust systematically increases with increasing internal yield strength. We illustrate our results by predicting the flow regimes of two typical lavas: a Hawaiian lava with no interior yield strength and a Mount Etna lava with an interior yield strength. In particular, we find that the crust strength stops small volume breakouts of the Mount Etna lava, while large volume breakouts are stopped by the interior yield strength.
Tumour-inhibiting platinum(ii) complexes with aminoalcoholligands: biologically important transformations studied by micellar electrokinetic chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry
Authors: Schluga Petra , Hartinger Christian G. , Galanski Mathea S. , Meelich Kristof , Timerbaev Andrei R. , Keppler Bernhard K.
Published: August 2005

The influence of the measurement environment on the transformation of pH sensitive anticancer platinum complexes was studied.
Leishmania major encodes an unusual peroxidase that is a close homologue of plant ascorbate peroxidase: a novel role of the transmembrane domain
Authors: Adak Subrata , Datta Alok K.
Published: August 2005

Haem-containing enzymes (peroxidase and catalase) are widely distributed among prokaryotes and eukaryotes and play a vital role in H2O2 detoxification. But, to date, no haem-containing enzymatic defence against toxic H2O2 has been discovered in Leishmania species. We cloned, expressed and purified an unusual plant-like APX (ascorbate peroxidase) from Leishmania major (LmAPX) and characterized its catalytic parameters under steady-state conditions. Examination of its protein sequence indicated approx. 30–60% identity with other APXs. The N-terminal extension of LmAPX is characterized by a charged region followed by a stretch of 22 amino acids containing a transmembrane domain. To understand how the transmembrane domain influences the structure–function of LmAPX, we generated, purified and extensively characterized a variant that lacked the transmembrane domain. Eliminating the transmembrane domain had no impact on substrate-binding affinity but slowed down ascorbate oxidation and increased resistance to H2O2-dependent inactivation in the absence of electron donor by 480-fold. Spectral studies show that H2O2 can quickly oxidize the native enzyme to compound (II), which subsequently is reduced back to the native enzyme by an electron donor. In contrast, ascorbate-free transmembrane domain-containing enzyme did not react with H2O2, as revealed by the absence of compound (II) formation. Our findings suggest that the single copy LmAPX gene may play an important role in detoxification of H2O2 that is generated by endogenous processes and as a result of external influences such as the oxidative burst of infected host macrophages or during drug metabolism by Leishmania.
A VEGF/JAK2/STAT5 axis may partially mediate endothelial cell tolerance to hypoxia
Authors: Dudley Andrew C. , Thomas David , Best James , Jenkins Alicia
Published: August 2005

Perturbation of oxygen flow occurs in disease states such as diabetic retinopathy and cancer. To maintain oxygen homoeostasis, the mammalian microvascular endothelium undergoes a dramatic reorganization to assist in bringing oxygen and nutrients to oxygen-starved tissues. This process is termed angiogenesis and is common in certain cancers with hypoxic foci and in areas of focal ischaemia in the diabetic retina. In the present study, we report on the activation of the JAK2/STAT5 pathway (where JAK stands for Janus kinase and STAT stands for signal transduction and activator of transcription) by low oxygen in microvascular endothelial cells. This activation appears to occur downstream of VEGF (vascular endothelial growth factor), a well-known proangiogenic factor, and is related to repression of proapoptotic FAS(CD95)/FASL(CD95L). These results indicate that the JAK/STAT pathway may play a pivotal role during tumour-associated or retinal angiogenesis in which endothelial cell survival during tissue hypoxia is critical for maintaining either the growth of neoplasms or the inappropriate retinal neovascularization common in diabetic retinopathy.
Isolation, subunit composition and interaction of the NDH-1 complexes from Thermosynechococcus elongatus BP-1
Authors: Zhang Pengpeng , Battchikova Natalia , Paakkarinen Virpi , Katoh Hirokazu , Iwai Masako , Ikeuchi Masahiko , Pakrasi Himadri B. , Ogawa Teruo , Aro Eva-Mari
Published: August 2005

NDH (NADH-quinone oxidoreductase)-1 complexes in cyanobacteria have specific functions in respiration and cyclic electron flow as well as in active CO2 uptake. In order to isolate NDH-1 complexes and to study complex–complex interactions, several strains of Thermosynechococcus elongatus were constructed by adding a His-tag (histidine tag) to different subunits of NDH-1. Two strains with His-tag on CupA and NdhL were successfully used to isolate NDH-1 complexes by one-step Ni2+ column chromatography. BN (blue-native)/SDS/PAGE analysis of the proteins eluted from the Ni2+ column revealed the presence of three complexes with molecular masses of about 450, 300 and 190 kDa, which were identified by MS to be NDH-1L, NDH-1M and NDH-1S respectively, previously found in Synechocystis sp. PCC 6803. A larger complex of about 490 kDa was also isolated from the NdhL-His strain. This complex, designated ‘NDH-1MS’, was composed of NDH-1M and NDH-1S. NDH-1L complex was recovered from WT (wild-type) cells of T. elongatus by Ni2+ column chromatography. NdhF1 subunit present only in NDH-1L has a sequence of -HHDHHSHH- internally, which appears to have an affinity for the Ni2+ column. NDH-1S or NDH-1M was not recovered from WT cells by chromatography of this kind. The BN/SDS/PAGE analysis of membranes solubilized by a low concentration of detergent indicated the presence of abundant NDH-1MS, but not NDH-1M or NDH-1S. These results clearly demonstrated that NDH-1S is associated with NDH-1M in vivo.
NMR structural analysis of a peptide mimic of the bridging sheet of HIV-1 gp120 in methanol and water
Authors: Chakraborty Kausik , Shivakumar P. , Raghothama S. , Varadarajan Raghavan
Published: August 2005

gp120 is a subunit of the Env (viral envelope protein) of HIV-1. The protein consists of inner and outer domains linked by a bridging sheet. Several gp120 residues that bind the neutralizing antibody 17b as well as the cellular co-receptor CCR5 (CC chemokine receptor 5), are located in the bridging sheet. Peptides that mimic the 17b-binding regions of gp120 would be useful potential immunogens for the generation of neutralizing antibodies against HIV-1. Towards this end, a 26-residue, four-stranded β-sheet peptide was designed on the basis of the structure of the bridging sheet, and its structure was characterized in methanol by NMR. In methanol, amide and α-proton resonances were well resolved and dispersed. A number of interstrand NOEs (nuclear Overhauser effects) were observed, providing good evidence for multiple turn β-hairpin structure. NOEs also provided good evidence for all Xxx–D-Pro bonds in the trans configuration and all three turns formed by a two residue D-Pro–Gly segment to be of type II′ turn. The structure conforms well to the designed four-stranded β-sheet structure. Approx. 20% of the peptide was estimated to adopt a folded conformation in water, as evidenced by CD spectroscopy. This was consistent with smaller, but still significant, downfield shifts of CαH protons relative to random-coil values. A second peptide was designed with two disulphide bonds to further constrain the peptide backbone. While structured in methanol, this peptide, like the previous one, also exhibits only partial structure formation in water, as evidenced by CD spectroscopy.
Catalysis of potato epoxide hydrolase, StEH1
Authors: Elfström Lisa T. , Widersten Mikael
Published: August 2005

The kinetic mechanism of epoxide hydrolase (EC 3.3.2.3) from potato, StEH1 (Solanum tuberosum epoxide hydrolase 1), was studied by presteady-state and steady-state kinetics as well as by pH dependence of activity. The specific activities towards the different enantiomers of TSO (trans-stilbene oxide) as substrate were 43 and 3 μmol·min−1·mg−1 with the R,R- or S,S-isomers respectively. The enzyme was, however, enantioselective in favour of the S,S enantiomer due to a lower Km value. The pH dependences of kcat with R,R or S,S-TSO were also distinct and supposedly reflecting the pH dependences of the individual kinetic rates during substrate conversion. The rate-limiting step for TSO and cis- and trans-epoxystearate was shown by rapid kinetic measurements to be the hydrolysis of the alkylenzyme intermediate. Functional characterization of point mutants verified residues Asp105, Tyr154, Tyr235 and His300 as crucial for catalytic activity. All mutants displayed drastically decreased enzymatic activities during steady state. Presteady-state measurements revealed the base-deficient H300N (His300→Asn) mutant to possess greatly reduced efficiencies in catalysis of both chemical steps (alkylation and hydrolysis).
Modification of blood cell PrP epitope exposure during prion disease
Authors: Thackray Alana M. , Ryder Stephen J. , Bujdoso Raymond
Published: August 2005

PrPC [normal cellular PrP (prion-related protein)] is a glycosylphosphatidylinositol-linked cell-surface glycoprotein that is expressed primarily by cells of the central and peripheral nervous system and the lymphoreticular system. During prion disease, PrPC undergoes structural modification to PrPSc (abnormal disease-specific conformation of PrP). The appearance of prion infectivity and PrPSc within different peripheral lymphoid tissue sites during natural scrapie infection in sheep is suggestive of haematogenic dissemination. For this to occur, blood cells may harbour or carry disease-associated PrP and in doing so present altered conformations of PrP on their cell-surface. In the present study, we show that changes in PrP epitope expression, or accessibility, can be detected on peripheral blood mononuclear cells during the course of experimental scrapie in susceptible sheep. Peripheral blood mononuclear cells isolated from VRQ homozygous lambs inoculated orally with scrapie were probed with either N- or C-terminal-specific anti-PrP monoclonal antibodies and analysed by flow cytometry. During the progression of scrapie, significant alterations were seen in the exposure of particular cell-surface PrP epitopes. These modifications included increased accessibility to N-terminal regions of the PrP molecule, to the region between β-strand-2 and residue 171, and to the C-terminal region of helix-3. Increased accessibility in the globular C-terminal domain of PrP occurred in the vicinity of tyrosine dimers, which are believed to have increased solvent exposure in disease-associated PrP. We suggest that the alterations in anti-PrP monoclonal antibody recognition of cell-surface PrP on blood cells from scrapie-infected sheep are indicative of structural changes within this molecule that may be relevant to prion disease.
Decay of isotropic turbulence: Fixed points and solutions for nonconstant G∼Rλ palinstrophy
Authors: Ristorcelli J. R. , Livescu D.
Published: August 2005

A Rλ scaling for the palinstrophy coefficient, G, has been observed in grid turbulence by Antonia et al. [J. Turbulence3, 1 (2002)]. As a consequence it appears that there exist decay laws other than the self-preserving Taylor-microscale decay of Speziale and Bernard [J. Fluid Mech.241, 645 (1992)], for which G is constant. Analytic solutions of Ristorcelli [Phys. Fluids15, 3248 (2003)], for the self-similar Taylor microscale decay, are modified to apply to the G∼Rλ decay. The solution indicates an asymptotic k(t)∼t−1 and a Rt→Rt∞ behavior, as seen in the self-preserving Taylor microscale decay. There are two important differences between the two decays: (1) the fixed point Rt∞ and (2) its rate of approach are substantially smaller for the G∼Rλ decay. It appears that the observation of an asymptotic k(t)→t−1 decay with Rt→const is not a demonstration of Taylor microscale self-similarity, and is achieved, at a much later time, in a wider class of flows. This appears to explain the absence of observations of a k(t)∼t−1 decay in wind tunnel data. It is speculated that the distinction between the G=const self-similar Taylor microscale decay and the G∼Rλ decay may be useful large eddy simulation test cases.
Vortex shedding in high Reynolds number axisymmetric bluff-body wakes: Local linear instability and global bleed control
Authors: Sevilla A. , Martínez-Bazán C.
Published: August 2005

In the present work we study the large-scale helical vortex shedding regime in the wake of an axisymmetric body with a blunt trailing edge at high Reynolds numbers, both experimentally and by means of local, linear, and spatiotemporal stability analysis. In the instability analysis we take into account the detailed downstream evolution of the basic flow behind the body base. The study confirms the existence of a finite region of absolute instability for the first azimuthal number in the near field of the wake. Such instability is believed to trigger the large-scale helical vortex shedding downstream of the recirculating zone. Inhibition of vortex shedding is examined by blowing a given flow rate of fluid through the base of the slender body. The extent of the locally absolute region of the flow is calculated as a function of the bleed coefficient, Cb=qb/(πR2u∞), where qb is the bleed flow rate, R is the radius of the base, and u∞ is the incident free-stream velocity. It is shown that the basic flow becomes convectively unstable everywhere for a critical value of the bleed coefficient of Cb*∼0.13, such that no self-excited regime is expected for Cb>Cb*. In addition, we report experimental results of flow visualizations and hot-wire measurements for increasing values of the bleed coefficient. When a sufficient amount of base bleed is applied, flow visualizations indicate that vortex shedding is suppressed and that the mean flow becomes axisymmetric. The critical bleed coefficient predicted by linear instability analysis is shown to fall within the experimental values in the range of Reynolds numbers analyzed here.
Analysis of mean momentum flux in subgrid models of turbulence
Authors: Li Yi , Meneveau Charles
Published: August 2005

Using a recently proposed model spectrum for weakly sheared turbulence [M. Ishihara, K. Yoshida, and Y. Kaneda, Phys. Rev. Lett. 88, 154501 (2002)], the mean momentum fluxes caused by subgrid scales are evaluated analytically. Using the result to calibrate the Smagorinsky coefficient, the value obtained is remarkably close to the traditional result obtained from balancing kinetic energy dissipation. For the Gaussian filter, the same conclusion is obtained when the Smagorinsky model is supplemented with the nonlinear model. It is concluded that when in practice the Smagorinsky model does not correctly predict the mean subgrid scale (SGS) stresses in large eddy simulation (LES), it must be due to either nonuniversal effects at large scales, or due to strong shear that violates the model spectrum assumed in the present analysis. Analysis of a two-parameter mixed model shows that the nonlinear term must be weighted more strongly in high shear conditions than in weak shear.
Response to “Comment on ‘Evaluating the law of the wall in two-dimensional fully developed turbulent channel flows’  ” [Phys. Fluids 16, 3507 (2004)]
Authors: Zanoun E.-S. , Durst F. , Nagib H. M.
Published: August 2005

Comments by Buschmann and Gad-el-Hak on Zanoun, Durst, and Nagib [ Phys. Fluids 15, 3079 (2003) ] provide an opportunity to clarify some of the statements in our paper as well as to comment on their views on the subject and their approach to “a generalized log law.”
Poisson’s ratio of the fcc hard sphere crystal at high densities
Authors: Tretiakov Konstantin V. , Wojciechowski Krzysztof W.
Published: August 2005

Elastic constants and the Poisson ratio of the fcc hard-sphere crystalline phases, free of defects and with vacancies, are determined by two Monte Carlo methods: (i) the analysis of the box fluctuations in the constant pressure ensemble with variable box shape (N-P-T) and (ii) by the free-energy differentiation with respect to deformation in the fixed box ensemble (N-V-T). Very good agreement is observed for the extrapolated to the infinitely large system limit results of both the methods. The coefficients of the leading singularities of the elastic constants near close packing are estimated; they are well described by the free volume approximation. Two mechanisms influencing the Poisson ratio are studied. (i) It is shown that at high densities particle motions decrease the Poisson ratio with respect to the static case which corresponds to zero temperature. Simulations performed for systems of soft spheres, interacting through n-inverse-power potentials, r−n, show that the elastic constants of the hard spheres can be obtained in the limit n→∞. When T→0 the elastic constants of the soft spheres tend to those of the static model. (ii) It is also shown that vacancies decrease C11 and C44 and increase C12 and, hence, increase the Poisson ratio with respect to the defect-free state of the system.
Coherent epitaxial growth and superhardness effects of c-TiN∕h-TiB2 nanomultilayers
Authors: Mei Fanghua , Shao Nan , Wei Lun , Dong Yunshan , Li Geyang
Published: August 2005

TiN ∕ TiB 2 nanomultilayers with different TiB2 layer thicknesses were deposited by the multitarget magnetron sputtering method. Studies show that because of the template effects of the cubic TiN layer, the normally amorphous TiB2 layer crystallizes into a compact hexagonal structure when its thickness is less than 2.9 nm. As a result, the multilayers form a c-TiN∕h-TiB2 coherent epitaxial structure with the orientation relationship of {111}TiN∕∕{0001}TiB2,⟨110⟩TiN∕∕⟨112¯0⟩TiB2. Correspondingly, the multilayers show a significant hardness enhancement with a maximum hardness of 46.9 GPa. Further increase in TiB2 layer thickness leads to the formation of amorphous TiB2 that blocks the coherent growth of the films, and thus the hardness of the multilayers decreases gradually.
Proposal for a “spin capacitor”
Authors: Datta Supriyo
Published: August 2005

We propose a “spin capacitor” that could be implemented by modifying a commercial silicon field-effect transistor to incorporate traps in the oxide and ferromagnetic source and drain contacts in an antiparallel spin-valve configuration. A quantitative model is presented suggesting that small values of drain voltage ∼100mV can be used to spin polarize the traps (“charge the spin capacitor”), which can be subsequently detected through its effect on the drain current. Other configurations can be designed to implement the basic idea, which enables convenient manipulation and detection of individual spins through a small applied bias and which may be useful in exploring many novel spintronic phenomena.
Controlled p- and n-type doping of Fe2O3 nanobelt field effect transistors
Authors: Fan Zhiyong , Wen Xiaogang , Yang Shihe , Lu Jia G.
Published: August 2005

Pure α-Fe2O3 nanobelts are configured as field effect transistors and electrical transport studies demonstrate their n-type behavior. In order to control the electrical properties of the fabricated transistor, the nanobelt channels are doped with zinc. Depending on the doping condition, α-Fe2O3 nanobelts can be modified to either p-type or n-type with enhanced conductivity and electron mobility. Such behavior change is exhibited in the variation of the current-voltage (I-V) and I-Vg characteristics.
Theoretical investigation of nonadiabatic and internal temperature effects on the collision-induced multifragmentation dynamics of Na5+ cluster ions
Authors: Sizun Muriel , Aguillon François , Sidis Victor
Published: August 2005

In a continued effort to disentangle adiabatic, nonadiabatic, and internal temperature effects in the collision-induced multifragmentation of alkali-metal cluster ions at moderate energies, we report a theoretical study of this process for the Na5++He encounter in the 100eV (center-of-mass) collision energy range. The investigation makes use of a diatomics-in-molecules based nonadiabatic molecular-dynamics (NAMD) method. All of the ten electronic A′1 molecular states of the cluster that can be formed by assembling ground-state monomers are considered explicitly. Cross sections for the corresponding 12 possible fragmentation channels are determined. As in the Na4++He case, we find that a few-channel characteristic of adiabatic fragmentation in the electronic ground state dominates. This owes primarily to the dominance of impulsive adiabatic mechanisms. Nonetheless, two significant nonadiabatic transitions take place: electronic excitation during the collision and electronic deexcitation in the postcollision stage. A large amount of the electronic excitation subsequently relaxes into the electronic ground state during the postcollision stage. This important intramolecular vibrational relaxation (IVR)-type mechanism enhances the population of channels characteristic of adiabatic fragmentation in the electronic ground state. The populations of the fragmentation channels are quite sensitive to the internal cluster temperature. This is discussed in terms of the conditions of occurrence of the fragmentation mechanisms and their competition. Comparisons with experimental results are presented and discussed.
New Raman method for aqueous solutions: ξ-function dispersion evidence for strong F−-water H–bonds in aqueous CsF and KF solutions
Authors: Walrafen George E.
Published: August 2005

The Raman ξ-function dispersion method recently elucidated for the strong H-bond breaker, ClO4−, in water [G. E. Walrafen, J. Chem. Phys. 122, 094510 (2005)] is extended to the strongly H-bond forming ion, F−. Measuring the ξ function is analogous to measuring ΔG from the thermodynamic activity of the water, aH2O, as the stoichiometric mol fraction of the water in the solution decreases due to addition of an electrolyte or nonelectrolyte. ξ is the derivative of the OH-stretching part of the Gibbs free energy with respect to the water mol fraction; ξω≡−RT[∂ln(Iω∕IREF)∕∂X2]T,P. I is the Raman intensity at ω (ω=Raman shift in cm−1); IREF, that at an arbitrary reference ω; and, X2 is the water mol fraction (X1=CsF or KF mol fraction). ln(Iω∕IREF) was found to be linear in X2 for the complete range of OH-stretching ω’s, with correlation coefficients as large as 0.999 96. Linearity of ln(Iω∕IREF) versus X2 is an experimental fact for all ω’s throughout the spontaneous Raman OH-stretching contour; this fact cannot be negated by relative contributions of ultrafast/fast, homogeneous/inhomogeneous processes which may underlie this linearity. Linearity in ln(Iω∕IREF) versus 1∕T, or in ln(Iω∕IREF) versus P, was also observed for the Raman H-bond energy ΔE and pair volume ΔV dispersions, respectively. A low-frequency maximum (MAX) and a high-frequency minimum (MIN) were observed in the ξ function dispersion curve. Δξ=ξMIN−ξMAX values of −7000±800-cal∕mol H2O for CsF, and the experimentally equal Δξ=−6400±1000-cal∕mol H2O for KF, were obtained. These Δξ’s are opposite in sign but have nearly the same absolute magnitude as the Δξ value for NaClO4 in water; Δξ=+8050±100-cal∕mol H2O. A positive Δξ corresponds to a water-water H-bond breaker; a negative Δξ to a H-bond former; specifically, a F−-water H-bond former, in the instant case. NaClO4 breaks water-water H-bonds and also gives rise to weak, long (3.0–3.3Å), severely bent (≈140°), high-energy, ClO4−-water interactions. Fluoride ion scavenges the extremely weak or non-hydrogen-bonded OH groups, thus forming strong, short, linear, low-energy, H-bonds between F− and water. The strength of the F−-water H-bond is evident from the fact that the OH-stretching ξ-function minimum is centered ≈200–300cm−1 below that of ice. The diagnostic feature of the Raman spectrum from F− in water is an intense, long, low-frequency OH-stretching tail extending 800cm−1 or more below the 3300-cm−1 peak. A similar intense, long, low-frequency Raman tail is produced by the OH− ion, which is known to H-bond very strongly when protons from water are donated to its oxygen atom.
Use of patterned laser liftoff process and electroplating nickel layer for the fabrication of vertical-structured GaN-based light-emitting diodes
Authors: Wang Shui-Jinn , Uang Kai-Ming , Chen Shiue-Lung , Yang Yu-Cheng , Chang Shu-Cheng , Chen Tron-Min , Chen Chao-Hsuing , Liou Bor-Wen
Published: August 2005

The fabrication process and performance characteristics of a vertical-structured GaN-based light-emitting diode (VM-LED) employing nickel electroplating and patterned laser liftoff techniques are presented. As compared to regular LED, the forward voltage drop of the VM-LED at 20–80 mA is about 10%–21% lower, while the light output power (Lop) is more than twice in magnitude. Especially, the Lop exhibits no saturation or degradation at an injection current up to 520 mA which is about 4.3 times higher than that of the regular one. Substantial improvements in the VM-LEDs performances are mainly attributed to the use of metallic substrate which results in less current crowding, larger effective area, and higher thermal conductivity.
Tunable electroluminescent color for 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds
Authors: Cheng Gang , Zhang Yingfang , Zhao Yi , Liu Shiyong , Xie Zengqi , Xia Hong , Hanif Muddasir , Ma Yuguang
Published: August 2005

Exciplex emission is observed in electroluminescent (EL) spectrum of an organic light-emitting device (OLED), where 2, 5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds (trans-DPDSB), (8-hydroxyquinoline) aluminum, and N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) are used as light-emitting, electron-transporting, and hole-transporting layers, respectively. This emission can be dramatically weakened by inserting a hole-injecting layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) between the hole-transporting layer and the anode. Consequently, EL color of this OLED is tuned from white to blue. This phenomenon may result from the improvement of hole injection, which shifts the major recombination zone from the NPB/trans-DPDSB interface to the trans-DPDSB layer.
How adiabatic is activated adsorption/associative desorption?
Authors: Luntz A. C. , Persson M.
Published: August 2005

Using density-functional theory we calculate friction coefficients describing the damping of nuclear motion into electron-hole pair excitation for the two best-known examples of activated adsorption: H2 dissociation on a Cu(111) surface and N2 dissociation on a Ru(0001) surface. In both cases, the frictions increase dramatically along the reaction path towards the transition state and can be an order of magnitude larger there than typical in the molecularly adsorbed state. In addition, the frictions for N2/Ru(0001) are typically an order of magnitude larger than for H2/Cu(111). We rationalize these trends in terms of the electron structure as the systems proceed to dissociation along the reaction paths. Combining these friction coefficients with the potential-energy surface in quasiclassical dynamics allows first-principles studies of the importance of the breakdown in the Born-Oppenheimer approximation in describing the chemistry. We find that nonadiabatic effects are minimal for the H2/Cu(111) system, but are quite important for N2/Ru(0001).
Insertion of noble-gas atom (Kr and Xe) into noble-metal molecules (AuF and AuOH): Are they stable?
Authors: Ghanty Tapan K.
Published: August 2005

The structure and the stability of a new class of insertion compounds of noble-gas atoms of the type AuNgX (Ng=Kr, Xe and X=F, OH) have been investigated theoretically through ab initio molecular-orbital calculations. All the species are found to have a linear structure with a noble-gas–noble-metal bond, the distance of which is comparable to covalent bond length except the AuKrOH system, for which it lies in between the covalent and van der Waals limits. The dissociation energies corresponding to the lowest-energy fragmentation products, AuX+Ng have been computed to be −166.2, −276.0, −194.4, and −257.6 kJ/mol for AuXeF, AuKrF, AuXeOH, and AuKrOH, respectively, at the MP2 level of theory. The respective barrier heights corresponding to the bent transition states (Au–Ng–X bending mode) have been calculated to be 119.1, 74.9, 160.7, and 141.6 kJ/mol. However, three of these species are found to be metastable in their respective potential-energy surface, and the dissociation energies corresponding to the Au+Ng+X fragments have been calculated to be 112.9, 3.0, and 18.7 kJ/mol for AuXeF, AuKrF, and AuXeOH, respectively, at the same level of theory. An analysis of the nature of interactions involved in the Au–Ng–X systems has been performed using Bader’s topological theory of atoms-in-molecules (AIM). Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of Au–Ng bonds in these systems. This work might have important implications in the preparation of a new class of insertion compounds of noble-gas atoms containing noble-gas–noble-metal bond.
Why the hydration energy of Au+ is larger for the second water molecule than the first one: Skewed orbitals overlap
Authors: Lee Han Myoung , Diefenbach Martin , Suh Seung Bum , Tarakeshwar P. , Kim Kwang S.
Published: August 2005

Using molecular-orbital analysis, we have elucidated the quantum-chemical origin of the intriguing phenomena in sequential hydration energies of the gold cation, which is known to be the most conspicuous among all transition metals. The hydration energy of Au+ with the second water molecule is found to be much larger than that with the first water molecule. Owing to the large relativistic effect of gold (i.e., significant lowering of the 6s orbital energy and significant raising of the 5d orbital energy), the highest occupied molecular orbital of the hydrated gold cation has a large portion of the 6s orbital. As the electron density of the 6s orbital populates in a large outer spherical shell far off the gold nucleus, the p orbitals (or sp hybridized lone-pair orbitals) of the water molecules are able to overlap with the outer part of the 6s orbital in the dihydrated gold cation, resulting in the unusual skewed overlap of p-6s-p orbitals (not the atom-to-atom bond overlap). No previous molecular-orbital analysis has reported this peculiar skewed orbitals overlap. Since this skewed orbitals overlap is saturated with two water molecules, this property is responsible for the low coordination number of the gold ion.
Photodissociation dynamics of formyl fluoride (HFCO) at 193 nm: Branching ratios and distributions of kinetic energy
Authors: Lee Shih-Huang , Wu Chia-Yan , Yang Sheng-Kai , Lee Yuan-Pern
Published: August 2005

Following photodissociation of formyl fluoride (HFCO) at 193 nm, we detected products with fragmentation translational spectroscopy utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Among three primary dissociation channels observed in this work, the F-elimination channel HFCO→HCO+F dominates, with a branching ratio ∼0.66 and an average release of kinetic energy ∼55kJmol−1; about 17% of HCO further decomposes to H+CO. The H-elimination channel HFCO→FCO+H has a branching ratio ∼0.28 and an average release of kinetic energy ∼99kJmol−1; about 21% of FCO further decomposes to F+CO. The F-elimination channel likely proceeds via the S1 surface whereas the H-elimination channel proceeds via the T1 surface; both channels exhibit moderate barriers for dissociation. The molecular HF-elimination channel HFCO→HF+CO, correlating with the ground electronic surface, has a branching ratio of only ∼0.06; the average translational release of 93kJmol−1,∼15% of available energy, implies that the fragments are highly internally excited. Detailed mechanisms of photodissociation are discussed.
Pyroelectric study of polarization switching in Langmuir-Blodgett films of poly(vinylidene fluoride trifluoroethylene)
Authors: Sorokin A. V. , Fridkin V. M. , Ducharme Stephen
Published: August 2005

The ferroelectric switching in Langmuir-Blodgett films of poly(vinylidene fluoride trifluoroethylene) is studied. The films have a distribution of switching times several decades wide. Nearly a half of the film volume may be switched faster than 1ms, though complete switching of a whole sample may require 100s or more. The switching occurs through a domain nucleation and growth mechanism. The decay of polarization at zero bias is logarithmic in time, with a constant rate below 5% per decade at room temperatures. The coercive voltage may be as low as 5V, which makes the films promising for use in nonvolatile random-access data storage.
Maleic anhydride adsorption on silicon (001)
Authors: Miotto R. , Ferraz A. C. , Srivastava G. P.
Published: August 2005

The adsorption of maleic anhydride on the Si(001) surface has been investigated using the first-principles pseudopotential formalism. Our total-energy calculations suggest that maleic anhydride (C2H2–C2O3) adsorbs preferentially through a [2+2] cycloaddition of the CC bond ([2+2]) with an adsorption energy of around 42kcal∕mol. Besides the [2+2] configuration we have also considered other possible coverages and adsorption models, including the adsorption on inter-row and intrarow dimer sites. Based on the analysis of the relative stability of different adsorption models, we propose the formation of mixed domains, containing the [2+2] unit and an interdimer unit. The comparison of our calculated electronic band structure, vibrational modes, and scanning tunneling microscopy images for the [2+2] and the favored interdimer adsorbed structures corroborate our proposed mixed domain model.
Theoretical characterization of charge transport in chromia (α-Cr2O3)
Authors: Iordanova N. , Dupuis M. , Rosso K. M.
Published: August 2005

Transport of conduction electrons and holes through the lattice of α-Cr2O3 (chromia) is modeled as a valence alternation of chromium cations using ab initio electronic structure calculations and electron-transfer theory. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus’ theory. The calculation of the electronic coupling followed the generalized Mulliken-Hush approach using the complete active space self-consistent-field (CASSCF) method and the quasidiabatic method. Our findings indicate that hole mobility is more than three orders of magnitude larger than electron mobility in both (001) and [001] lattice directions. The difference arises mainly from the larger internal reorganization energy calculated for electron-transport relative to hole-transport processes while electronic couplings have similar magnitudes. The much larger hole mobility versus electron mobility in α-Cr2O3 is in contrast to similar hole and electron mobilities in hematite α-Fe2O3 previously calculated. Our calculations also indicate that the electronic coupling for all charge-transfer processes of interest is smaller than for the corresponding processes in hematite. This variation is attributed to the weaker interaction between the metal 3d states and the O(2p) states in chromia than in hematite, leading to a smaller overlap between the charge-transfer donor and acceptor wave functions and smaller superexchange coupling in chromia. Nevertheless, the weaker coupling in chromia is still sufficiently large to suggest that charge-transport processes in chromia are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron-spin coupling within the Cr-Cr donor-acceptor pair, while the reorganization energy is essentially independent of the electron-spin coupling.
Characteristic features of Shannon information entropy of confined atoms
Authors: Sen K. D.
Published: August 2005

The Shannon information entropy of 1-normalized electron density in position and momentum space Sr and Sp, and the sum ST, respectively, are reported for the ground-state H, He+, Li2+, H−, He, Li+, Li, and B atoms confined inside an impenetrable spherical boundary defined by radius R. We find new characteristic features in ST denoted by well-defined minimum and maximum as a function of confinement. The results are analyzed in the background of the irreducible lower bound stipulated by the entropy uncertainty principle [I. Bialynicki-Birula and J. Mycielski, Commun. Math. Phys. 44, 129 (1975)]. The spherical confinement model leads to the ST values which satisfy the lower bound up to the limits of extreme confinements with the interesting new result displaying regions over which a set of upper and lower bounds to the information entropy sum can be locally prescribed. Similar calculations on the H atom in 2s excited states are presented and their novel characteristics are discussed.
Electron transfer collisions between isolated fullerene dianions and SF6
Authors: Neumaier Marco , Hampe Oliver , Kappes Manfred M.
Published: August 2005

Electron transfer collisions of trapped doubly charged fullerene anions C762−, C782−, and C842− with SF6 are studied in a Fourier transform ion cyclotron resonance mass spectrometer at center-of-mass collisional energies ranging from thermal energy to 77 eV. Collision energy dependencies manifest threshold energies for (nominally exoergic) single electron transfer onto SF6 of 1.46±0.3eV, 1.56±0.3eV, and 1.63±0.3eV for C762−, C782−, and C842−, respectively. Kinetics studies reveal charge-transfer cross sections of up to 430±200Å2 for C842− at a collision energy of 77 eV. The mechanism and the energetics are discussed in terms of classical electrostatic model calculations. Additionally, we rationalize the collision energy dependencies of the charge-transfer cross sections using the two-state Landau-Zener formalism to describe the associated resonant electron tunneling probability.
Characterization of long-range surface-plasmon-polariton waveguides
Authors: Berini P. , Charbonneau R. , Lahoud N. , Mattiussi G.
Published: August 2005

Measurements of the attenuation and excitation efficiency of the long-range surface-plasmon-polariton mode supported by waveguides comprised of one or many thin metal films of finite width embedded in dielectric were made in the near infrared (λ0=1550nm). Au films 31, 25, and 20 nm thick, and Ag films 20 nm thick were used to implement the structures. The lowest attenuations measured among the Au and Ag waveguides are 0.42 and 0.32dB∕mm, respectively, corresponding to propagation lengths of 10 340, and 13572μm, respectively. These propagation lengths are longer than those of the single-interface surface-plasmon polariton in the corresponding semi-infinite structures by factors of 93 and 138, respectively. These factors are the largest reported to date for long-range surface-plasmon-polariton waves. The largest excitation efficiency measured among the set of Au structures is 98%. Theoretical results were obtained for all of the structures characterized experimentally using an accurate electromagnetic-field model. Theory and experiment agree to within about 5% over the 31- and 25-nm-thick Au structures, but a thickness-dependant permittivity must be assumed in order to achieve agreement to within 12% for the 20-nm Au structures.
Plasma diffusion across a magnetic field observed by collective light scattering: Experimental evidence for Lévy stable distributions
Authors: Lemoine Nicolas , Grésillon Dominique M.
Published: August 2005

On a toroidal magnetized plasma discharge, ToriX, a collective light-scattering device has been set to investigate plasma turbulence and transport. The scattering device output signal is proportional to the space Fourier transform of the plasma density. The two-dimensional static form factor, at the scale of the scattering wave number k, is measured in absolute units as a function of k. It shows that fluctuations are large and mainly situated at large scales. By adding a small vertical component to the main toroidal magnetic field, a uniform plasma has been achieved and the form factor is significantly reduced. The time autocorrelation function of the scattered signal as a function of k is shown to be the Fourier transform of the displacement probability distribution. It is investigated at different times as a function of k and found to be consistent with a Lévy walk model with a characteristic exponent α closed to 1. The displacement probability distribution is thus close to a Lorentz function instead of a Gaussian.
Modeling of imaging diagnostics for laser plasma interaction experiments with the code PARAX
Authors: Lewis K. , Riazuelo G. , Labaune C.
Published: August 2005

We have developed a diagnostic simulation tool for the code PARAX to interpret recent measurements of far-field images of the laser light transmitted through a preformed plasma. This includes the complete treatment of the propagation of the light coming from a well-defined region of plasma through the rest of the plasma and all the optics of the imaging system. We have modeled the whole light path, as well as the spatio-temporal integration of the instruments, and the limited collecting aperture for the light emerging out of the plasma. The convolution of computed magnitudes with the plasma and diagnostics transfer functions is indispensable to enable the comparison between experiments and simulations. This tool is essential in the study of the propagation of intense laser beams in plasma media.
ZnO p-n homojunctions and ohmic contacts to Al–N-co-doped p-type ZnO
Authors: Zhuge F. , Zhu L. P. , Ye Z. Z. , Ma D. W. , Lu J. G. , Huang J. Y. , Wang F. Z. , Ji Z. G. , Zhang S. B.
Published: August 2005

ZnO p-n homojunctions were fabricated on quartz substrates by depositing Al-doped n-type ZnO layer on Al–N-co-doped p-type ZnO layer through reactive magnetron sputtering. In/Zn metal contacts to as-grown ZnO show ohmic behavior, and the ohmic contacts can be improved by annealing in an Ar ambient. The optimal annealing temperatures for Al–N-co-doped ZnO and Al-doped ZnO are 550 °C and 600 °C, respectively. The p-n junction characteristic is confirmed by current-voltage measurements. The turn-on voltage is 2 V, with a low leakage current under reverse bias. Series resistances of the ZnO p-n junctions can be lowered by optimizing the annealing temperature, increasing the grain size of the ZnO, or increasing the hole concentration of the p layer.
Enhanced contrast radiography with channel-cut crystals at the LNLS
Authors: Hönnicke M. G. , Kellerman G. , Rocha H. S. , Giles C. , Tirao G. , Mazzaro I. , Lopes R. T. , Cusatis C.
Published: August 2005

An analyzer-based x-ray phase contrast imaging (PCI) setup based on channel-cut crystals at the Laboratorio Nacional de Luz Sincrotron (LNLS—Brazilian Synchrotron) is presented. The contrast, visibility, signal-to-noise ratio and spatial resolution of the acquired images were characterized. The potential of PCI for enhancing details of different features with the same x-ray attenuation coefficient is exploited together with cross section simulations of the PCIs acquired at different angular positions on the rocking curve (RC). The present results show that this setup can be used as a standard PCI setup at the LNLS.