bluuebunny/crossref_metadata_2025 huggingface dataset:
Why do Both Parents Incubate in the Kentish Plover?
Authors: Kosztolányi András , Székely Tamás , Cuthill Innes C.
Published: August 2003

Incubation by both parents is a common parental behaviour in many avian species. Biparental incubation is expected if the survival prospects of offspring are greatly raised by shared care, relative to the costs incurred by each parent. We investigated this proposition in the Kentish ploverCharadrius alexandrinus, in which both parents incubate the clutch, but one parent (either the male or the female) usually deserts after hatching of the eggs. We carried out a mate‐removal and food supplementation experiment to reveal both the role of the sexes and food abundance in maintaining biparental incubation by removing either the male or the female from the nest for a short period of time. In some nests we provided supplementary food for the parent that remained at the nest to reduce the costs of incubation, whereas other nests were left unsupplemented. Although males spent more time on incubation after their mate had been removed, females’ incubation did not change. Notwithstanding the increased male incubation, total nest attentiveness was lower at uniparental nests than at biparental controls. However, incubation behaviour was not influenced by food supplementation. We conclude that offspring desertion during incubation is apparently costly in the Kentish plover, and this cost cannot be ameliorated with supplementary food.
Vertical Position Reflects Increased Feeding Motivation in Growth Hormone Transgenic Coho Salmon (Oncorhynchus kisutch)
Authors: Fredrik Sundström L. , Devlin Robert H. , Johnsson Jörgen I. , Biagi Carlo A.
Published: August 2003

Growth hormone (GH) gene transgenesis has allowed the production of salmon with an inherently increased growth potential, on average two to threefold higher compared with daily specific growth rates observed in normal, non‐transgenic fish. This difference quickly results in animals of very different sizes at age, and is associated with specific morphological effects and enhanced appetites in transgenic animals. However, less is known of the feeding and antipredator behaviour of GH‐transgenic fish, information that can help with predictions of potential ecological consequences of release or escape of transgenic fish into the wild. In a series of experiments, transgenic (T) and normal (N) coho salmon of varying age and size (from 0.5 to 40 g, 3.5–21 mo) were studied singly, in pairs, and in groups during feeding and simulated predation threat. Vertical position generally did not differ between T and N fry, but at larger size (>4 g) T fish remained closer to the surface than N fish both during feeding and predatory attacks, probably as a consequence of inherent differences in feeding motivation and later reinforcement by associative learning. This difference in vertical position was not the result of competition as it remained even after either fish in the pair had been removed. In nature, where predators may attack from above (birds) or below (fish), this kind of behaviour may translate into higher risk of predation, which could increase mortality and lower the fitness of transgenic fish, unless their increased growth rate can compensate for the increased risk‐taking.
Effect of Risk on Aspects of Escape Behavior by a Lizard, Holbrookia propinqua, in Relation to Optimal Escape Theory
Authors: Cooper William E.
Published: August 2003

Prey must balance gains from activities such as foraging and social behavior with predation risk. Optimal escape theory has been successful in predicting escape behavior of prey under a range of risk and cost factors. The optimal approach distance, the distance from the predator at which prey should begin to flee, occurs when risk equals cost. Optimal escape theory predicts that for a fixed cost, the approach distance increases as risk increases. It makes no predictions about approach distance for prey in refuges that provide only partial protection or about escape variables other than approach distance, such as the likelihood of stopping before entering refuge and escape speed. By experimentally simulating a predator approaching keeled earless lizards, Holbrookia propinqua, the predictions of optimal escape theory for two risk factors, predator approach speed and directness of approach were tested. In addition, predictions that the likelihood of fleeing into refuge without stopping and the speed of escape runs increase with risk, in this case predator approach speed, and that lizards in incompletely protective refuges permit closer approach than lizards not in refuges were also tested. Approach distance increased with predator approach speed and directness of approach, confirming predictions of optimal escape theory. Lizards were more likely to enter refuge and ran faster when approached rapidly, verifying that predation risk affects escape decisions by the lizards for escape variables not included in optimal escape theory. They allowed closer approach when in incompletely protective refuges than when in the open, confirming the prediction that risk affects escape decisions while in refuge. Optimal escape theory has been highly successful, but testing it has led to relative neglect of important aspects of escape other than approach distance.
Motivational and Heritable Determinants of Dispersal Latency in Wild Male House Mice (Mus musculus musculus)
Authors: Krackow Sven
Published: August 2003

Divergence of dispersal regimens has been suggested to be the selective basis for the evolutionary differentiation of agonistic phenotypes found in natural populations of house mice. Dispersal propensity may, therefore, be expected to exhibit heritable variation in wild house mice, ultimately related to motivational differences causing observable differences in agonistic behaviour. To test for heritable components in dispersal propensity in wild house mice, father–offspring regressions of dispersal latencies from residential social groups were determined in standardized seminatural social settings. To evaluate potential motivational causes of phenotypic variation in dispersal behaviour, all test animals (fathers, sons, and daughters) were scored prior to the dispersal experiment in a standardized behavioural test, at 60 d of age. Activities were monitored in a 1 m2 square test arena during 10‐min observation periods. Test arenas exhibited four equidistant openings leading to cages containing fresh, own, sibling, or foreign bedding material. The apparatus allowed for scoring anxiety, exploratory activity, and kin preference. Subsequently, test animals were exposed to a resident population in a semi‐natural enclosure providing a dispersal opportunity. Father–son regressions of dispersal latencies were significantly positive, but no significant relationship was found for daughters. Dispersal latency decreased with increasing exploratory activity scores in males, but increased in females. Anxiety as well as kin preferences did not affect dispersal propensity. Hence sex‐linked, motivational components reflect heritable social behaviour variation in male house mice that may ultimately be caused by diverging dispersal regimens.
Abundance of boll worm, flower beetle, predators and field colonization by Rhynocoris kumarii (Het., Reduviidae) following mulching and shelter provisioning in cotton
Authors: Claver M. A. , Kalyanasundaram M. , David P. M. M. , Ambrose D. P.
Published: August 2003

Abstract:  Field colonization of the assassin bug Rhynocoris kumarii Ambrose and Livingstone and biocontrol potential of predatory arthropods after mulching with sorghum trash and coconut leaflets and with shelter provisioning with pieces of clay pots and stones was studied in a cotton field experiment at the Agricultural College Farm, Killikulam, South India. Third and fourth nymphal instars of R. kumarii were released. There were fewer Helicoverpa armigera Hübner larvae in plots with mulched cotton trash than in control and other (mulched and shelter provisioned) plots. But mulching did not affect the number of adult Mylabris pustulata Thunberg. The flower and boll damage was significantly less in trash and leaflet mulch plots than in other shelter provisioned and control plots. The percentage of good quality cotton was also greater in mulch plots than in control plots. The yield of seed‐cotton was also significantly greater in plots with trash mulches and coconut leaflet mulches than in control plots.
Antifeedant and toxic activity of Adhatoda vasica leaf extract against Spodoptera littoralis (Lep., Noctuidae)
Authors: Sadek M. M.
Published: August 2003

Abstract: The effect of crude methanolic extracts of Adhatoda vasica leaves on the feeding and performance of Spodoptera littoralis larvae was investigated in the laboratory. Feeding on fresh leaves resulted in 100% mortality of larvae after 26 days of unsubstantial growth. The extract exhibited strong antifeedant and toxic activity against the larvae when applied either on leaf discs or incorporated into artificial diet. Under choice conditions the antifeedant index calculated over 72 h for neonate larvae increased significantly (from 71.5 ± 3.2 to 92.1 ± 4.2) as the concentration of extract in the treated diet increased from 200 to 1000 ppm. Consumption by the sixth instar larvae of leaf discs dipped in 0.01, 0.1 and 0.2% extract solutions was significantly lower than consumption of control discs in both choice and no‐choice tests. The latter two concentrations deterred feeding by 63.4 and 90.4%, respectively, under choice conditions, while only the 0.2% extract solution deterred feeding by 56.8% in the no‐choice test. Toxicity of the extracts was manifested by a high mortality, reduced growth rates, and low weight gain by larvae fed on diets containing 200–2000 ppm of the extract. No larvae survived to pupation under the latter concentration. The time to pupation increased from 15.8 ± 0.4 to 37.9 ± 4.1 days as the extract concentration in diet increased from 0 to 1000 ppm. When fed to the fifth instar larvae, the crude extract significantly reduced consumption, growth, utilization of ingested and digested food, and approximate digestibility. The consumption‐dependent growth efficiency of animals fed on extract‐free diet was significantly higher than the growth efficiency of animals fed on extract‐containing diets, suggesting both antifeedant and toxic activities of the extract.
Targeting T‐cell subsets to achieve remission
Authors: Christophers E
Published: August 2003

Patients with psoriasis have an increase in pathogenic CD45RO+ memory‐effector T cells during active disease. The genetically engineered fully human fusion protein alefacept has been developed to selectively target this subset of T cells. Alefacept binds to memory‐effector CD45RO+ T cells, inhibiting their activation and inducing T‐cell apoptosis. The selectivity of alefacept for memory‐effector CD45RO+ T cells was evaluated in 229 patients with chronic psoriasis in a randomized, placebo‐controlled, double‐blind study conducted at 22 centres in the USA. Patients received alefacept intravenously at doses of 0.025 mg/kg, 0.075 mg/kg, or 0.150 mg/kg, or placebo once weekly for 12 weeks. Two weeks after completing treatment, patients receiving alefacept showed significant improvement in the Psoriasis Area and Severity Index (PASI) compared with those receiving placebo. Mean reductions in the PASI score were up to 53% lower than baseline scores in the alefacept treatment group, compared with a 21% decline from baseline in the placebo group (P < 0.001). In addition to the significant improvement in psoriasis, treatment with alefacept produced long‐term remission in some patients. Twelve weeks after completion of therapy, 28 patients became clear or almost clear. The therapy was well tolerated and nonimmunogenic. Importantly, during treatment, there was a correlation between improvement in psoriasis and a dose‐dependent reduction in peripheral blood CD45RO+ memory‐effector T cells, but not in CD45RA+ naive T cells. This correlation indicates a relationship between a specific T‐cell subset reduction (CD45RO+) and clinical outcome in psoriasis.
Radio-frequency-driven near atmospheric pressure microplasma in a hollow slot electrode configuration
Authors: Yu Zengqi , Hoshimiya Katsumi , Williams John D. , Polvinen Steven F. , Collins George J.
Published: August 2003

We report hollow electrode geometries that support near atmospheric (89 kPa) microdischarges in Ar and Ar–air mixtures when excited at 13.56 MHz with rf voltages of 50–230 V. The slot dimensions are 200 μm wide by 400–600 μm deep and 3–35 cm in length. Optical emission along the slot length is uniform in intensity at applied rf power levels up to 10 W/cm of slot length under the experimental conditions described herein. When metal electrodes are employed, we can draw 0.18 A/cm of self-bias dc current into the rf-driven plasma. Measurements of the electrode self-bias dc voltage level indicate operation in both negative as well as positive self-bias discharge modes. The latter mode, to our knowledge, has not been reported previously in rf microdischarges at near atmospheric pressures.
Magnetotransport properties of alkali metal doped La–Ca–Mn–O system under pulsed magnetic field: Decrease of small polaron coupling constant and melting of polarons in the high temperature phase
Authors: Bhattacharya Sayani , Pal S. , Banerjee Aritra , Yang H. D. , Chaudhuri B. K.
Published: August 2003

Pulsed magnetic field (0–4.4 T) was used to study the magnetic field dependent resistivity (12–350 K) and thermoelectric power (0–1.5 T) of Na and K-doped La0.7Ca0.7−yAyMnO3 (0.0⩽y⩽0.3, A=Na, K) system showing semiconducting to metallic transitions around temperature Tp. Na/K-doping increases both conductivity and Tp. In La1−xCaxMnO3, an increase of Tp and conductivity with an increase of Ca (for x⩽0.33) are small and the small polaron coupling constant (γ) and hence the electron-lattice (phonon) interaction is strong. But in the Na/K doped system, γ is small and for y⩾0.05, Motts’ condition of strong el–ph interaction breaks down in the high temperature (T>Tp) phase. Increase of conductivity in the Na/K doped system is caused by the decrease of γ, binding energy (Wp), hopping energy (WH), and effective mass (mp) of the polarons leading to the melting (we call it) of polarons in the T>Tp phase. This melting results in an increase of exchange coupling constant between spins. Field dependent thermoelectric power (TEP) of the samples (measured between 80–300 K) also supports the small polaron hopping conduction. The resistivity data are well fitted with the variable range hopping model for a limited range of temperature (Tp<T<θD/2, θD being the Debye temperature) while thermally activated small polaron hopping model is found valid for T>θD/2. With the application of a magnetic field, the density of states at the Fermi level increases. The TEP data indicate the importance of electron-magnon contribution in the low temperature (TTp.
Quantum control design via adaptive tracking
Authors: Zhu Wusheng , Rabitz Herschel
Published: August 2003

An adaptive tracking algorithm is developed to achieve quantum system control field designs. The adaptive algorithm has the advantage of operating noniteratively to efficiently find desirable controls, and has the feature of high stability by suppressing the influence of disturbances from tracking singularities. The core of the adaptive tracking control algorithm is a self-learning track switch technique which is triggered by monitoring of the evolving system trajectory. The adaptive tracking algorithm is successfully tested for population transfer.
Electronic structure of linear TiCH
Authors: Kalemos Apostolos , Dunning Thom H. , Harrison James F. , Mavridis Aristides
Published: August 2003

The linear TiCH molecule is studied by ab initio quantum mechanical calculations using quantitative basis sets and highly correlated computational methods. Potential energy curves along the Ti−CH coordinate have been computed to obtain a better understanding of molecular formation in eight low-lying states of the molecule. Total energies, dissociation energies (with respect to Ti+CH), equilibrium distances, and dipole moments are reported. Simple valence bond Lewis diagrams are used to interpret the nature of the bonding in all of the states studied.
Translational and rotational dynamics of water in mesoporous silica materials: MCM-41-S and MCM-48-S
Authors: Faraone Antonio , Liu Li , Mou Chung-Yuan , Shih Pei-Chun , Copley John R. D. , Chen Sow-Hsin
Published: August 2003

We investigated the translational and rotational dynamics of water molecules in mesoporous silica materials MCM-41-S and MCM-48-S using the incoherent quasielastic neutron scattering technique. The range of wave vector transfers Q covered in the measurements was from 0.27 to 1.93 Å−1 broad enough to detect both the translational and rotational contributions to the scattering. We used the relaxing-cage models for both translational and rotational motions which we developed earlier, to analyze the QENS spectra and investigated water dynamics in a supercooled range from 250 to 280 K. The results show a marked slowing down of both the translational and rotational relaxation times, and an increasing effect of confinement on the translational motion, as the temperature is lowered.
Correlation of the physical properties and the interface morphology of AlGaAs/GaAs heterostructures
Authors: Gottwaldt L. , Pierz K. , Ahlers F. J. , Göbel E. O. , Nau S. , Torunski T. , Stolz W.
Published: August 2003

We have investigated the influence of interface roughness in GaAs/AlGaAs heterostructures on both the optical and the electronic properties by systematically varying the two growth parameters substrate temperature and growth interruption. We prove that the optimization of samples for optics and transport, respectively, requires different growth parameters. Whereas the optical properties are exclusively determined by the roughness of the two quantum well interfaces, the transport properties are additionally influenced by the ionized impurity scattering. The number of impurities increases during growth interruption and, consequently, in contrast to the optical samples, an optimization of the growth parameters is not as straightforward since it depends on the background impurities originating from the ultrahigh vacuum system. A direct correlation with information obtained from atomic force microscopy images is therefore only possible for the optical properties. At growth temperatures higher than 620 °C in addition to the usual terrace structure, a mesoscopic island structure appears and dominates the exciton luminescence linewidth.
Enhanced low field magnetoresistive response in (La2/3Sr1/3MnO3)x/(CeO2)1−x composite thick films prepared by screen printing
Authors: Valencia S. , Castaño O. , Fontcuberta J. , Martı́nez B. , Balcells Ll.
Published: August 2003

The magnetoresistance and magnetization of (La2/3Sr1/3MnO3)x(LSMO)/(CeO2)1−x (0.64⩽x⩽1) composite thick films have been studied as a function of the manganite concentration. It is found that for high LSMO content, when the applied magnetic field is perpendicular to the film plane, the attainable low field magnetoresistance (LFMR) response is drastically reduced due to demagnetizing field effects. These effects are suppressed when the concentration of CeO2 is increased, thus an enhancement of the LFMR is observed. These results can be very important for developing magnetic sensors working in the low magnetic field regime when magnetic field needs to be applied perpendicular to the film plane.
The predissociation of highly excited states in acetylene by time-resolved photoelectron spectroscopy
Authors: Zamith S. , Blanchet V. , Girard B. , Andersson J. , Sorensen S. L. , Hjelte I. , Björneholm O. , Gauyacq D. , Norin J. , Mauritsson J. , L’Huillier A.
Published: August 2003

We study the dynamics of highly excited states in acetylene initiated by an ultrashort vacuum ultraviolet laser pulse. Electronic states lying in the 4s-3d Rydberg region are excited with one femtosecond pulse, and the dynamic development of the states is monitored by a second short pulse which ionizes the system. We show that even for femtosecond pulses where the bandwidth of the exciting pulse covers several electronic states, it is possible to extract short decay lifetimes through time-resolved photoelectron spectroscopy by using a frequency-modulated (chirped) excitation pulse. We report decay lifetimes for the F 402 and E 4-502 states in acetylene, and for the E 402 and E 502 states in d-acetylene. The time evolution measured in the electron spectra is compared to decay spectra measured using ion yield and the differences in these results are discussed.
Ammonia-chain clusters: Vibronic spectra of 7-hydroxyquinoline⋅(NH3)2
Authors: Coussan Stéphane , Manca Carine , Tanner Christian , Bach Andreas , Leutwyler Samuel
Published: August 2003

Mass- and isomer-selected S1←S0 resonant two-photon ionization and S1→S0 fluorescence spectra were measured for the 7-hydroxyquinoline⋅(NH3)2 [7HQ⋅(NH3)2] and d2-7-hydroxyquinoline⋅(ND3)2 clusters cooled in supersonic expansions. UV/UV hole burning measurements prove that a single cluster isomer is formed. Ab initio self-consistent field and density functional calculations predict that the most stable cluster form has an “ammonia wire” hydrogen bonded to the –OH and N groups of the cis-7HQ rotamer. The experimental S0 and S1 frequencies are in very good agreement with the calculated normal mode frequencies for both the normal and deuterated ammonia-wire clusters. S1←S0 excitation leads to contractions of the –O–H⋯N and NH3⋯NH3 hydrogen bonds, as well as smaller displacements for the NH3⋯N(quinoline) stretch and the in plane rotation (or bend) of the ammonia dimer relative to 7HQ. The coupling of these modes to the S1←S0 electronic excitation indicates that hydrogen bond contractions in the excited state are important and may be prerequisite for the S1 state proton transfer processes that occur in the larger 7HQ⋅(NH3)n (n⩾4) clusters. The calculated electron density differences upon S1←S0 excitation show large π-electron flows on the 7HQ moiety. However, the σ-electronic rearrangements that directly drive the hydrogen bond rearrangements are one to two orders of magnitude smaller.
Hole mobility enhancements in nanometer-scale strained-silicon heterostructures grown on Ge-rich relaxed Si1−xGex
Authors: Lee Minjoo L. , Fitzgerald Eugene A.
Published: August 2003

Although strained-silicon (ε-Si) p-type metal–oxide–semiconductor field-effect transistors (p-MOSFETs) demonstrate enhanced hole mobility compared to bulk Si devices, the enhancement has widely been observed to degrade at large vertical effective fields. We conjecture that the hole wave function in ε-Si heterostructures spreads out over distances of ∼10 nm, even at large inversion densities, due to the strain-induced reduction of the out-of-plane effective mass. Relevant experimental and theoretical studies supporting this argument are presented. We further hypothesize that by growing layers thinner than the hole wave function itself, inversion carriers can be forced to occupy and hybridize the valence bands of different materials. In this article, we show that p-MOSFETs with thin (i.e., <3 nm) ε-Si layers grown on Ge-rich Si1−xGex buffers exhibit markedly different mobility enhancements from prior ε-Si p-MOSFETs. Devices fabricated on a thin ε-Si layer grown on relaxed Si0.3Ge0.7 demonstrate hole mobility enhancements that increase with gate overdrive, peaking at a value of nearly 3 times. In other devices where the channel region consists of a periodic ε-Si/relaxed Si0.3Ge0.7 digital alloy, a nearly constant mobility enhancement of 2.0 was observed over inversion densities ranging from 3 to 14×1012/cm2.
Properties of thin film silicon nitride deposited by hot wire chemical vapor deposition using silane, ammonia, and hydrogen gas mixtures
Authors: Mahan A. H. , Dillon A. C. , Gedvilas L. M. , Williamson D. L. , Perkins J. D.
Published: August 2003

The structure of thin film SiN, deposited by the hot wire chemical vapor deposition (HWCVD) technique using SiH4 and NH3 gas mixtures, is examined as H2 dilution is added to the gas flow mixture. For NH3/SiH4 gas flow ratios greater than 1/2, all films are a-SiN:H for H2/SiH4 gas dilution ratios as high as 20/1. While H2 dilution does not change the basic film structure, it does increase the efficiency of NH3 dissociation in the gas phase, and causes a further reduction in the already small amount of N-H bonding in a-SiN:H films deposited by HWCVD. Differences in local N bonding sites are observed when the nitrogen source gas is changed from NH3 to N2. For NH3/SiH4 gas ratios less than 1/2 and with high H2 dilution, deposition of μc-SiN by HWCVD is demonstrated. X-ray diffraction measurements show that the structure of these films consists of silicon crystallites embedded in an a-SiN:H matrix. An upper limit for N incorporation with the preservation of microcrystallinity is found, beyond which the films again become amorphous. The existence of this limit is explained in terms of structural disorder in the a-SiN:H tissue brought about by N incorporation.
Generating functionals, consistency, and uniqueness in the integral equation theory of liquids
Authors: Fantoni R. , Pastore G.
Published: August 2003

We discuss and illustrate through numerical examples the relations between generating functionals, thermodynamic consistency (in particular the virial-free-energy one), and uniqueness of the solution in the integral equation theory of liquids. We propose an approach for deriving closures automatically satisfying such characteristics. Results from a first exploration of this program are presented and discussed.
Hydrophobic effect in a lattice model of aqueous solutions
Authors: Buzano C. , Pretti M.
Published: August 2003

We investigate a simple lattice fluid model of aqueous solutions in the mean-field approximation. In this model water molecules possess a tetrahedral symmetry with four bonding arms, and bond formation depends on both molecule orientations and local density. As far as water is concerned, the model is similar to the one proposed by Roberts and Debenedetti [J. Chem. Phys. 105, 658 (1996)], simplified in that no distinction between bond “donors” and “acceptors” is imposed. We first show that even the simplified model, at such a low approximation stage, is able to reproduce several anomalous properties of liquid water. Moreover, we consider the insertion of quite a generic (monomer) model solute and derive solvation thermodynamics in the dilute solution limit. For an inert solute we observe qualitative features that are typical of the hydration of apolar (hydrophobic) molecules.
Quantum chemical analysis of the bond lengths in fn and fn−1d1 states of Ce3+, Pr3+, Pa4+, and U4+ defects in chloride hosts
Authors: Barandiarán Zoila , Seijo Luis
Published: August 2003

It is widely believed that impurity–ligand bond distances in lanthanide (Ln) and actinide (An) doped crystals, are larger in the fn−1d1 energy levels than in the fn ones. This idea, which was not justified and is probably based on the fact that Ln 5d (An 6d) orbitals have a radial extent much larger than Ln 4f (An 5f ) orbitals, has been neither confirmed nor rejected experimentally in spite of the fact that a very large number of absorption/emission spectroscopic studies on f-element doped hosts exist, because the band shapes depend on the square of the bond length offsets between initial and final electronic states. Recent quantum chemical calculations on Ln and An impurities in fluoride and chloride cubic hosts, which considered host embedding, dynamic electron correlation, and relativistic spin–free and spin–orbit coupling effects, have shown that impurity–ligand bond distances are classified in three sets according to their configuration, with the following trend: Re[fn−1d(t2g)1]<Re[fn]<Re[fn−1d(eg)1], in contradiction with the assumed expectations. In this paper we give an interpretation of this, on the basis of a constrained space orbital variation analysis of the chemical bond in states of the fn, fn−1d(t2g)1, and fn−1d(eg)1 configurations of four model systems: Cs2NaYCl6:Ce3+, Cs2NaYCl6:Pr3+, Cs2ZrCl6:Pa4+, and Cs2ZrCl6:U4+. The analysis shows that the basic difference between fn and fn−1d1 configurations regarding bond effects which are responsible for the bond distance is that, in the former, all the open-shell electrons are shielded from the ligands by the 5p (6p) filled shell and the bond length is determined by closed-shell interactions between the outermost Ln 5p6 (An 6p6) shell and the ligands, whereas in the latter one electron has crossed the 5p (6p) barrier and is much more exposed to bonding interactions with the ligands, at the same time that an internal 4f (5f ) hole has been created which induces ligand to Ln (An) charge transfer, all of it resulting in the shown trends.
2-methyl furan: An experimental study of the excited electronic levels by electron energy loss spectroscopy, vacuum ultraviolet photoabsorption, and photoelectron spectroscopy
Authors: Giuliani A. , Delwiche J. , Hoffmann S. V. , Limão-Vieira P. , Mason N. J. , Hubin-Franskin M.-J.
Published: August 2003

The vacuum ultraviolet absorption spectrum of 2-methyl furan has been recorded between 5 eV (248 nm) and 9.91 eV (125 nm) and absolute photoabsorption cross sections measured. The electronic excited states of the molecule have also been probed using high resolution electron energy loss spectroscopy. Recorded under electric–dipole conditions, it has confirmed the magnitude of the photoabsorption cross section values and extended the optical oscillator strength values up to 12 eV. Measurements at several scattering angles have allowed the angular behavior of differential cross section ratios for some features in the 5–7.1 eV region to be measured, which in turn have helped in the assignments of electronic states to observed absorption bands. A high-resolution photoelectron spectrum was measured and allowed the two lowest ionization energies to be determined, these have been used in the identification of the related Rydberg states. Vibrational fine structure in the photoelectron spectrum has also been analyzed. The spectrum is dominated by intense π–π* transitions. Rydberg series associated with the first and second ionization energies have been identified. The effects of symmetry reduction induced on the furan ring by the methyl substitution are also discussed.
Photoinduced inclination of polyimide molecules containing azobenzene in the backbone structure
Authors: Sakamoto Kenji , Usami Kiyoaki , Kanayama Takashi , Kikegawa Manabu , Ushioda Sukekatsu
Published: August 2003

We have investigated the inclined alignment of polyimide molecules (containing azobenzene in the backbone structure) induced by oblique angle irradiation of ultraviolet (UV) light. The UV irradiation was performed for a polyamic acid film, which then was thermally converted into a polyimide film. The orientation of the polyimide backbone structure was determined by measuring the polarized infrared absorption spectra as a function of the angle of incidence. We confirmed that inclined alignment of the polyimide backbone structures is obtained by oblique angle UV irradiation, and that this also induces tilted homogeneous liquid crystal (LC) alignment. For the UV irradiation conditions used in the present study, the average inclination angle of the polyimide backbone structure was about 4° from the surface plane. The pretilt angle of the LC molecules was 0.9°.
Laser interaction with a pair of two-dimensional coupled quantum dots
Authors: Carvalho C. R. , Jalbert Ginette , Rocha A. B. , Brandi H. S.
Published: August 2003

We study the effects of a laser on the splitting of the lowest electronic states of a pair of two-dimensional (2D) GaAs-(Ga,Al)As coupled quantum dots, in the presence of a homogeneous external magnetic field. The interaction of light with the 2D quantum dots is treated within a dressed-band approach in which a two-band scheme is used to model the GaAs bulk semiconductor whereas the interaction with the laser field is treated through the renormalization of the semiconductor energy gap and conduction/valence effective masses. This approach is valid far from resonances and has been successfully used to treat other confined semiconductor heterostructures. We focus our attention on the splitting of the lowest singlet and triplet states and on their double occupation probability. We analyze the exchange coupling (J) in the effective Heisenberg model as a function of the laser field and its detuning, as well as of the magnetic field (B) within the Heitler-London approximation of molecular physics. We find that due to the electronic confinement the laser may play a role similar to the external magnetic field in the qualitative behavior of the exchange parameter J. Furthermore, the presence of the laser may assure both the sizable exchange coupling and the vanishingly small double occupation probability required for efficient quantum computer operations, even in the absence of an external magnetic field. Besides being of fundamental interest, these features may be used as an efficient two-qubit gate control.
Thermal activation of two-level systems in a polymer glass as studied with single-molecule spectroscopy
Authors: Bauer M. , Kador L. , Naumov A. V. , Vainer Yu. G.
Published: August 2003

Fluorescence excitation spectroscopy of single chromophores in an amorphous polymer at low temperatures allows the study of single two-level systems (TLSs) of the matrix. With increasing temperature, more TLSs are thermally activated and contribute to random flipping, splitting, and/or broadening of single-molecule lines. In this paper we report on temperature-dependent changes of the intensity ratio between different components of single-molecule lines. The system under study is tetra-tert-butyl-terrylene in poly-isobutylene. Since the temperature dependent changes are due to thermal activation of individual TLSs, we could calculate the asymmetry of several of these TLSs yielding values between 0.25 and 1.5 meV. Some of the TLSs do not follow the Boltzmann activation law.
Reaction dynamics of Al+O2→AlO+O studied by the crossed-beam laser-induced fluorescence technique
Authors: Honma Kenji
Published: August 2003

Dynamics of the reaction, Al+O2→AlO+O, was studied by using the crossed-beam technique at five collision energies from 6.9 to 25.3 kJ/mol. The Al atomic beam was generated by laser vaporization and crossed with the O2 beam at a right angle. The product AlO was detected by laser-induced fluorescence of the AlO(B 2Σ+–X 2Σ+) transition and the rotational-vibrational distributions were determined. The observed rotational and vibrational distributions displayed greater populations in lower vibrational and rotational levels than expected statistically. Rotational distributions were also determined for two spin–orbit states of Al, Al(2P1/2) and Al(2P3/2), at two collision energies. At a collision energy of 12.2 kJ/mol, the higher energy spin–orbit excited state, Al(2P3/2), showed lower reactivity, i.e., about one-third of the ground spin–orbit state, Al(2P1/2). However, the rotational distributions for the two states were almost identical. Both the reactivity and rotational distributions for Al(2P1/2) and Al(2P3/2) became similar at a higher collision energy, 18.5 kJ/mol. These results suggest that the reaction of Al with O2 proceeds via an intermediate complex. Both spin–orbit states lead to the complex, lose memory of the initial electronic state, and provide identical rotational distributions.
Square-well chain fluids: The thermodynamic properties of hexamers, octamers, and hexadecamers
Authors: Porter James A. , Fridrikh Sergey V. , Lipson J. E. G.
Published: August 2003

The thermodynamic and statistical properties of square-well hexamers, octamers, and hexadecamers have been studied using the Born–Green–Yvon method. We have obtained concentration- and temperature-dependent site–site correlation functions for each system and have used these results to predict the equation of state and the phase diagram. Where possible we have compared our results with those obtained using Monte Carlo simulations and other theoretical methods.
Contact pair correlation functions of binary mixtures of additive hard spheres from the virial expansion
Authors: Barrio C. , Solana J. R.
Published: August 2003

Density expansions of the contact pair correlation functions for binary mixtures of additive hard spheres are obtained from the virial expansion of the equation of state. The procedure is based on the use consistency conditions. The resulting expansions are exact up to first order in the density. This corresponds to the third virial coefficient which is exactly known for these mixtures. Analytical expressions for the second and third order terms are obtained on the basis of very accurate approximate analytical expressions for the fourth and fifth virial coefficients. It is found that the series converge slowly, but the convergency can be accelerated by means of a resummation procedure.
System size dependence of the free energy surface in cluster simulation of nucleation
Authors: Kusaka Isamu
Published: August 2003

We calculated the free energy of vapor phase nucleation in a truncated and shifted Lennard-Jones fluid by subjecting a small system taken inside the metastable phase to grand canonical Monte Carlo simulation and then estimating the probability distribution over the macrostates specified by global order parameters. The free energy surface determined by this method exhibits a strong dependence on the system volume. Despite this, the free energetics relevant to the prediction of steady-state nucleation rate is shown to remain unchanged over a wide range of the system size.
One photon dissociation and multiphoton dissociative ionization of bromochlorodifluoromethane (CF2BrCl) at 267 nm region
Authors: Huang Jianhua , Xu Dadong , Francisco Joseph S. , Jackson William M.
Published: August 2003

The photodissociation dynamics of CF2BrCl have been studied near 267 nm using time-of-flight mass spectrometry combined with ion velocity imaging. The bromine atoms are probed via 2+1 resonance enhanced multiphoton ionization. The one-photon dissociation channels of CF2BrCl produce bromine atoms in both ground state Br(2P3/2) and excited state Br(2P1/2). Translational energy and angular distributions for each channel are derived from the two-dimensional images of both of the bromine atoms using the back-projection method. The time of flight mass spectra indicate that the CF2Cl+ ions are also formed with the focused laser in the 259–270 nm region. Six images were taken in this wavelength region and they show the typical characteristics recently reported by several groups that are attributed to dissociative ionization arising from multiphoton absorption. The changes in the energy and angular distributions of CF2Cl+ as a function of wavelength are described in terms of a resonance enhanced multiphoton dissociative ionization mechanism involving excitation to Rydberg states above and below the ionization potential of CF2BrCl. The translational energy distributions at different wavelengths clearly indicate that there is a competition between neutral dissociation and dissociative ionization from the initial super-excited states reached by three photons. The angular distributions suggest that there exist strong coupling between Rydberg electron in p-type orbital and the ion core, which affects the spin–orbit coupling in the fragment Br atom. It is also proposed that curve crossing similar to that observed in the one photon dissociation between repulsive ionic states of CF2BrCl+ leads to the formation of both Br(2P3/2) and Br(2P1/2) as the counterparts of the observed CF2Cl+.
Ab initio calculations on the ground and low-lying excited states of InCl
Authors: Zou Wenli , Lin Meirong , Yang Xinzheng , Zhang Baozheng
Published: August 2003

All-electron relativistic calculations have been performed on the low-lying electronic states of InCl by using the internally contracted multireference singles and doubles configuration interaction with the Davidson correction method. The potential energy curves and the spectroscopic constants are obtained. The C 1Π1 state has also been studied by using other internally contracted multireference methods, and it is found that the spectroscopic constants can be well reproduced by the multireference average quadratic coupled cluster method. Moreover, the essentials that affect the spectroscopic properties of the C 1Π1 state are discussed. Besides the X 1Σ+, Π0−3, A 3Π0+, B 3Π1, Π23, and C 1Π1 states, some valence excited states with shallow minima close to each other and four Rydberg states are also obtained. With the aid of the theoretical results, some experimental weak bands are reanalyzed: it is proved that the so-called “D state” is not a single state in fact, but a set of closely spaced states with shallow potential wells, and the symmetry of the E state is predicted to be Π0+3.
High level ab initio studies of the low-lying excited states in the H2O⋅O2 complex
Authors: Robinson Timothy W. , Kjaergaard Henrik G.
Published: August 2003

The lowest energy electronic transitions in the weakly bound van der Waals complex of water and oxygen (H2O⋅O2) are studied using ab initio methods. The vertical excitation energies for the two low-lying singlet states are calculated with the complete active space self-consistent field and multireference configuration interaction (MRCI) methods, and are compared to those calculated in the oxygen molecule. The MRCI calculations predict blueshifts of about 150 and 250 cm−1 for the transition frequencies on formation of the complex. These calculated shifts can provide assistance towards the spectroscopic identification of H2O⋅O2.
Lithium ion insertion in nanoporous anatase TiO2 studied with RIXS
Authors: Augustsson A. , Henningsson A. , Butorin S. M. , Siegbahn H. , Nordgren J. , Guo J.-H.
Published: August 2003

Lithium insertion into nanoporous anatase TiO2 electrodes has been studied using resonant inelastic soft-x-ray scattering spectroscopy (RIXS). We have measured Ti 2p absorption, L2,3-emission and resonant inelastic scattering spectra of pristine anatase TiO2 and Li inserted TiO2. Inelastic scattering features in RIXS spectra of pristine TiO2 are assigned to charge-transfer excitations. Low energy-loss features for Li inserted TiO2 electrodes, appearing within t2g bands, due to d–d excitations, indicate the presence of Ti3+ states. The experimental observations suggest strong electron correlation in anatase TiO2 introduced by the Li-insertion.
Investigation of circular Bragg reflection in an azo polymer with photoinduced chirality
Authors: Hore Dennis , Wu Yiliang , Natansohn Almeria , Rochon Paul
Published: August 2003

There has been recent interest in photoinduced chirality in azo polymers upon irradiation with circularly polarized light. The mechanism of ordering is thought to involve successive twisting of the achiral photoactive azo-containing side chains in response to the handedness of the pump polarization. In this study, a thin film of a liquid-crystalline azo polymer with a room-temperature nematic phase is irradiated with circularly polarized light and a circular Bragg reflection is observed in the absorption spectrum. When probed at normal incidence, the evolution of this selective reflection is monitored with increasing exposure. Then, the probing is carried out for various angles of incidence and the change in peak shape is studied. In the last experiment, the position of the Bragg reflection is monitored as the wavelength of the pump laser is varied. We propose that while the induced chirality is due to the circularly polarized light, the associated pitch may be large; the induced periodicity corresponding to the Bragg reflection may be the result of partial erasure due to a standing wave created by back reflection in thin films.
Kinetic study of thermally induced electronic and morphological transitions of a wafer-bonded GaAs/GaAs interface
Authors: Shi Frank F. , Hsieh K. C.
Published: August 2003

Based upon temporal measurements of interface electrical conductivity from current–voltage characterization and interface micromorphologies from transmission electron microcopy, a kinetic analysis of the thermally induced interfacial transformation process of GaAs/GaAs semiconductor interfaces fabricated by wafer bonding technology is performed. The activation energy required for the overall interface transformation that involves defect and atomic diffusion was determined to be 0.75 eV. A physical model of this transformation process is proposed.
Comparison of the ablation plumes arising from ArF laser ablation of graphite, silicon, copper, and aluminum in vacuum
Authors: Claeyssens Frederik , Henley Simon J. , Ashfold Michael N. R.
Published: August 2003

The ablation plumes arising after irradiation of graphite, silicon, copper and aluminum with a pulsed nanosecond ArF (λ=193 nm) laser at fluences between 2 and 20 J cm−2 in vacuum are studied and compared. The neutral and ionic components in the ablation plume have been measured via quadrupole mass spectrometry and ion probes, respectively. Additional information about the degree of ionization and the velocities of singly and multiply charged ions in the plume have been deduced via optical emission spectrometry, and the electron velocity distributions have been measured with Langmuir probes. Probing the plasma properties with this range of techniques is shown to provide a rather detailed picture of the ablation characteristics. The velocity distributions of the neutral atoms are comparatively narrow (∼1 km s−1 full width at half maximum) and peaked at a center of mass velocity of ∼3–4 km s−1. Their general form is reminiscent of those of species expanding supersonically from a pulsed nozzle. The electron and ion velocity distributions are much broader, and centered at much higher velocities (and kinetic energies). The relative ion yield, and the overall degree of ionization, both increase with increasing fluence and scale inversely with the ionization potentials of the respective target materials. Both charged components are found to be accelerating at short distances from the target. Such effects have been rationalized by assuming that incident laser radiation ionizes (by multiphoton ionization) neutral species ablated from the target surface, and that these ions and electrons then act as “seeds” for subsequent plume heating, ionization and plasma formation by inverse bremsstrahlung. This absorption due to inverse bremsstrahlung ensures the incident laser intensity is highest at the outer edge of the expanding plume. The outer region thus receives preferential excitation and heating—traditionally pictured in terms of the so-called two electron temperature model. Some of the resulting “hot” electrons escape from this coronal region, leading to an overall charge imbalance within the plasma, which manifests itself as an acceleration (driven by Coulombic interactions) of the charged components within the plume.
Control of nitrogen incorporation in Ga(In)NAs grown by metalorganic vapor phase epitaxy
Authors: Derluyn J. , Moerman I. , Leys M. R. , Patriarche G. , Sęk G. , Kudrawiec R. , Rudno-Rudziński W. , Ryczko K. , Misiewicz J.
Published: August 2003

We report on our studies of the nitrogen incorporation behavior in GaNAs bulk layers and GaInNAs quantum wells, grown by metalorganic chemical vapor deposition. By high-resolution x-ray diffraction measurements on GaNAs, we observe that the nitrogen incorporation efficiency increases with increasing tertiary-butyl-arsine flow up to a certain threshold. Results on GaInNAs quantum wells (QWs) confirm this trend. Finally, we link the optical quality of these quantum wells to the abruptness of the QWs and the nitrogen content.