bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermo‐ and pH‐responsive gradient and block copolymers based on 2‐(2‐methoxyethoxy)ethyl methacrylate synthesized via atom transfer radical polymerization and the formation of thermoresponsive surfaces
Authors: Medel Sandra , Manuel García José , Garrido Leoncio , Quijada‐Garrido Isabel , París Rodrigo
Published: December 2010

A series of gradient and block copolymers, based on 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO2MA) and tert‐butyl acrylate (tBA), were synthesized by atom transfer radical polymerization (ATRP) in a first step. The MEO2MA monomer leads to the production of thermosensitive polymers, exhibiting lower critical solution temperature (LCST) at around room temperature, which could be adjusted by changing the proportion of tBA in the copolymer. In a second step, the tert‐butyl groups of tBA were hydrolyzed with trifluoroacetic acid to form the corresponding block and gradient copolymers of MEO2MA and acrylic acid (AA), which exhibited both temperature and pH‐responsive behavior. These copolymers showed LCST values strongly dependent on the pH. At acid pH, a slightly decrease of LCST with an increase of AA in the copolymer was observed. However, at neutral or basic conditions, ionization of acid groups increases the hydrophilic balance considerably raising the LCST values, which even become not observable over the temperature range under study. In the last step, these carboxylic functionalized copolymers were covalently bound to biocompatible and biodegradable films of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(HB‐co‐HHx)] obtained by casting and, previously treated with ethylenediamine (ED) to render their surfaces with amino groups. Thereby, thermosensitive surfaces of modified P(HB‐co‐HHx) could be obtained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Block copolymers via macromercaptan initiated ring opening polymerization
Authors: Lefay Catherine , Glé David , Rollet Marion , Mazzolini Jérôme , Bertin Denis , Viel Stéphane , Schmid Christina , Boisson Christophe , D'Agosto Franck , Gigmes Didier , Barner‐Kowollik Christopher
Published: December 2010

Poly(styrene) macromercaptanes (Mn = 1900, 3600, and 6100 g mol−1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D,L‐lactide under conditions of organo‐catalyis employing 4,4‐dimethylaminopyridine. Poly(styrene)‐block‐poly(lactide) polymers of number average molecular weights up to 25,000 g mol−1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D,L‐lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Rapid synthesis of block and cyclic copolymers via click chemistry in the presence of copper nanoparticles
Authors: Pressly Eric D. , Amir Roey J. , Hawker Craig J.
Published: December 2010

A new method for the rapid and efficient coupling of homopolymers to yield diblock and triblock copolymers as well as cyclic polymers using the 3 + 2 π Huisgen copper catalyzed cycloaddition reaction has been developed. This facile method utilizes commercially available Cu nanoparticles that are tolerant to O2, easily removable and recyclable. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Exciton behaviours in doped tris (8‐hydroxyquinoline) aluminum (Alq3) films
Authors: Uddin A. , Lee C. B.
Published: December 2010

The doping effect on exciton behaviours in amorphous tris (8‐hydroxyquinolinato) aluminum (Alq3) were studied for the first time by transient photoluminescence (PL) measurements at room temperature. The dopants 4‐(diacynomethylene)‐2‐methyl‐6‐(p‐dimethylaminostyryl)‐4H‐pyan (DCM) and 5,6,11,12‐tetraphenylnaphthacene (rubrene) were used into Alq3 films at various concentration from 0.5 to 24 wt.% for this study. The exciton recombination rate was found sharply increased with doping concentration in Alq3 films. The exciton lifetime in pure Alq3 was found as ∼ 20 ns and it was reduced up to ∼8 ns with doping concentration. The exciton diffusion coefficient and diffusion length in doped films was found as 0.5 – 1.4 × 10–6 cm2 s–1 and 18–35 Å, respectively (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Amplified spontaneous edge‐ emissions from π‐conjugated polymer ultrathin films: Discrete or continuous energy detuning
Authors: Tomioka Akihiro , Kamiyama Yasushi , Iwamoto Kazuhisa , Anzai Takahiro , Takeuchi Takaya
Published: December 2010

π‐conjugated polymer film waveguides, with sufficient thickness to accept multiple waveguided modes, showed amplified spontaneous emissions (ASE's) detuned by as much as 240 meV, showing that the detuning was made on the basis of evanescent field leak into the substrate, consistent with our previous report on the detuning using a photonic crystal substrate, that should be strongest at the critical reflection angle of guided ASE field within the polymer waveguide. Still the ASE energy was selected as one of the discrete series of accompanying molecular vibrational transitions of the constituent polymer, indicating that the coupling is stronger between the vibrational transition and the photoexcited molecular polarization oscillating at the optical frequency than the coupling between this polarization and the waveguide mode. It is the extended π‐conjugation along the polymer backbone that connects the molecular vibrations with the molecular polarization. With higher photoexcitation, continuous detuning was also observed due to filling of the excited state. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An adaptive seamless phase II/III design for oncology trials with subpopulation selection using correlated survival endpoints†
Authors: Jenkins Martin , Stone Andrew , Jennison Christopher
Published: December 2010

Although the statistical methods enabling efficient adaptive seamless designs are increasingly well established, it is important to continue to use the endpoints and specifications that best suit the therapy area and stage of development concerned when conducting such a trial. Approaches exist that allow adaptive designs to continue seamlessly either in a subpopulation of patients or in the whole population on the basis of data obtained from the first stage of a phase II/III design: our proposed design adds extra flexibility by also allowing the trial to continue in all patients but with both the subgroup and the full population as co‐primary populations. Further, methodology is presented which controls the Type‐I error rate at less than 2.5% when the phase II and III endpoints are different but correlated time‐to‐event endpoints. The operating characteristics of the design are described along with a discussion of the practical aspects in an oncology setting. Copyright © 2010 John Wiley & Sons, Ltd.
Nonlinear data assimilation in geosciences: an extremely efficient particle filter
Authors: van Leeuwen P. J.
Published: December 2010

Almost all research fields in geosciences use numerical models and observations and combine these using data‐assimilation techniques. With ever‐increasing resolution and complexity, the numerical models tend to be highly nonlinear and also observations become more complicated and their relation to the models more nonlinear. Standard data‐assimilation techniques like (ensemble) Kalman filters and variational methods like 4D‐Var rely on linearizations and are likely to fail in one way or another. Nonlinear data‐assimilation techniques are available, but are only efficient for small‐dimensional problems, hampered by the so‐called ‘curse of dimensionality’. Here we present a fully nonlinear particle filter that can be applied to higher dimensional problems by exploiting the freedom of the proposal density inherent in particle filtering. The method is illustrated for the three‐dimensional Lorenz model using three particles and the much more complex 40‐dimensional Lorenz model using 20 particles. By also applying the method to the 1000‐dimensional Lorenz model, again using only 20 particles, we demonstrate the strong scale‐invariance of the method, leading to the optimistic conjecture that the method is applicable to realistic geophysical problems. Copyright © 2010 Royal Meteorological Society
Thermodynamic control of tropical cyclogenesis in environments of radiative‐convective equilibrium with shear
Authors: Rappin Eric D. , Nolan David S. , Emanuel Kerry A.
Published: December 2010

The potential for tropical cyclone formation from a pre‐existing disturbance is further explored with high‐resolution simulations of cyclogenesis in idealized, tropical environments. These idealized environments are generated from simulations of radiative‐convective equilibrium with fixed sea‐surface temperatures (SSTs), imposed mean surface winds, and an imposed profile of vertical wind shear. The propensity for tropical cyclogenesis in these environments is measured in two ways: first, in the period of time required for a weak, mid‐level circulation to transition to a developing tropical cyclone; and second, from the value of an incubation parameter that incorporates environmental measures of mid‐level saturation deficit and thermodynamic disequilibrium between the atmosphere and ocean. Conditions of tropospheric warming can be produced from increased SSTs or from increased mean surface winds; in either case, the time to genesis increases with atmospheric warming. As these parameters are varied, the incubation parameter is found to be highly correlated with changes in the time to genesis.

The high resolution (3 km) of these simulations permits analysis of changes in tropical cyclogenesis under warming conditions at the vortex scale. For increasing SST, increased mid‐level saturation deficits (dryness) are the primary reason for slowing or preventing genesis. For environments with increased surface wind, it is the decreased thermodynamic disequilibrium between the atmosphere and ocean that delays or prevents development. An additional effect in both cases is a decoupling of the low‐level and mid‐level vortices, primarily as a result of increased advecting flow at the altitude of the mid‐level vortex, which is linked to the height of the freezing level. Copyright © 2010 Royal Meteorological Society
Antioxidant enzyme activities and lipid peroxidation in earthworm Eisenia fetida exposed to 1,3,4,6,7,8‐hexahydro‐4,6,6,7,8,8‐hexamethyl‐cyclopenta‐γ‐2‐benzopyran
Authors: Liu Shuo , Zhou Qixing , Chen Chun
Published: December 2010

Polycyclic musks have been indicated to cause lethal and sublethal effects on exposed biota. However, knowledge about the effect of polycyclic musks on the antioxidant defense system in earthworms is vague. In this work, the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) exposed to 1,3,4,6,7,8‐hexahydro‐4,6,6,7,8,8‐hexamethyl‐cyclopenta‐γ‐2‐benzopyran (HHCB) were systematically investigated. The investigation shows that their activities are closely related to the exposed dose and time of HHCB. For SOD and CAT, the activities increased monotonically with increased exposed dose of HHCB, which indicates a dose‐dependent change pattern. POD exhibited its peak activity in 0.0157 μg cm−2 HHCB treatment and decreased at higher concentrations. These two changing patterns were complementary, which reveals the cooperation of enzymes in response to oxidative stress. MDA content in earthworms was basically unaffected with a 1‐day exposure and significantly increased after 2‐day and 3‐day exposures, correlating with changes in the activities of SOD and CAT when the concentration of HHCB was high. It was also found that the sensitivity of Eisenia fetida to HHCB increased over time. These results may support the theoretical hypothesis that oxidative stress is an important component for the response of earthworms to the toxicity of HHCB in environment. Among the studied enzymes, SOD and CAT appeared to be the most responsive biomarkers of oxidative stress caused by HHCB. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.
GC Separation of cis‐Eicosenoic Acid Positional Isomers on an Ionic Liquid SLB‐IL100 Stationary Phase
Authors: Ando Yasuhiro , Sasaki Tsubasa
Published: December 2010

Gas chromatography (GC) of cis‐eicosenoic acid (20:1) positional isomers has been investigated on a capillary column of ionic liquid 1,9‐di(3‐vinyl‐imidazolium)nonane bis(trifluoromethyl)sulfonylimidate stationary phase (SLB‐IL100). A test mixture of isomeric 20:1 methyl esters was prepared from flathead flounder flesh lipids. On a 60‐m column operated at 150–180 °C, six peaks appeared in the elution order of 20:ln‐15 → 20:ln‐13 → 20:ln‐11 → 20:ln‐9 → 20:ln‐7 → 20:ln‐5. These peaks were baseline resolved within 20 min at 180 °C. The 20:ln‐13 and 20:ln‐11 isomers, poorly resolved on conventional polar polysiloxane stationary phases, were completely separated from each other with separation factor α = 1.02 and peak resolution (Rs) ≥ 1.57. When equivalent chain length (ECL) values were compared between the SLB‐IL100 and CP‐Sil 88 (biscyanopropyl polysiloxane), those of 20:ln‐15 and 20:ln‐13 exceptionally tended to be lower on the SLB‐IL100. The excellent separation of 20:1 isomers seems due to less retention of 20:ln‐15 and 20:ln‐13 on SLB‐IL100 rather than simply due to its high polarity. Analysis of herring oil 20:1 revealed the occurrence of 20:ln‐13 in the Pacific herring but not in the Atlantic herring. The ionic liquid stationary phase, SLB‐IL100, is effective for analyzing 20:1 isomers occurring in fish and other natural oils.
Long-term outcome of slipped capital femoral epiphysis: A 38-year follow-up of 66 patients
Authors: Wensaas Anders , Svenningsen Svein , Terjesen Terje
Published: December 2010

Purpose

The purpose of this retrospective study was to evaluate the long-term outcome of different methods of treatment in slipped capital femoral epiphysis (SCFE), to find risk factors for poor outcome, and to assess whether prophylactic fixation is indicated.

Methods

Sixty-six patients (76 hips) treated for SCFE with a mean follow-up of 38 years (range 21–57 years) were evaluated. All except seven patients had chronic SCFE. Ten patients (15%) had bilateral affection. Three methods of treatment had been used: screw fixation (35 hips), bone-peg epiphysiodesis (30 hips), and bone-peg epiphysiodesis combined with corrective femoral osteotomy (11 hips). The long-term clinical outcome was classified as good when the patient had not undergone total hip replacement (THR), when the Harris hip score (HHS) was 85 points or above, or the patient had no pain. Good radiographic outcome was defined as no THR or osteoarthritis (OA).

Results

In 51 patients with chronic slip (mean slip angle 32°) treated with in situ fixation, the clinical outcome was good in 35 patients (69%) and there was no significant difference between screw fixation and bone-peg epiphysiodesis. Eight patients with large chronic slip (mean slip angle 53°) were treated with bone-peg epiphysiodesis and corrective femoral osteotomy, and the clinical outcome was poor in six patients. Seven patients with acute slip had larger mean slip angle (57°) and more complications than those with chronic slip, and the long-term outcome was poor in all. Two hips out of 42 (5%) had OA in the contralateral hip at follow-up.

Conclusion

In situ fixation of chronic SCFE gave satisfactory long-term outcome irrespective of the treatment method. Corrective femoral osteotomy did not improve the outcome in hips with large slip angles. Acute SCFE had poor outcome. Prophylactic fixation of the contralateral hip is barely necessary.
Conduct disorder symptoms and subsequent pregnancy, child‐birth and abortion: A population‐based longitudinal study of adolescents
Authors: Pedersen Willy , Mastekaasa Arne
Published: December 2010

Research on teenage pregnancy and abortion has primarily focused on socio‐economic disadvantage. However, a few studies suggest that risk of unwanted pregnancy is related to conduct disorder symptoms. We examined the relationship between level of conduct disorder symptoms at age 15 and subsequent pregnancy, child‐birth and abortion. A population‐based, representative sample of Norwegian adolescent girls (N = 769) was followed from early adolescence until their mid‐20s. Even with control for socio‐demographic and family variables, conduct disorder symptoms at age 15 were strongly associated with pregnancy in the 15–19 age group, and a weaker association persisted in the 20–28 age group. Similar results were obtained for abortions, but here a strong relationship with conduct disorder symptoms was found even after age 20. After adjustment, no significant association between conduct disorder symptoms and subsequent child‐birth was observed. More targeted preventive programmes aimed at girls with conduct disorder symptoms may be warranted.
A ‘sup + C inf’ inequality for the equation –Δu = V eu|x|2α
Authors: Bartolucci Daniele
Published: December 2010

We generalize the ‘sup+C inf’ inequality obtained by Shafrir to the solutions of

with Ω ⊂ ℝ2 open and bounded, α ∈ (0,1) and V any measurable function which satisfies 0 < a ≤ V ≤ b < + ∞.
Strong-Verb Paradigm Leveling in Four Germanic Languages: A Category Frequency Approach
Authors: Dammel Antje , Nowak Jessica , Schmuck Mirjam
Published: December 2010

We investigated strong-verb paradigm leveling in German, Dutch, English, and Swedish, and found significant differences in ablaut leveling and class change towards the weak conjugation. Swedish favors ablaut patterns retaining a difference between the preterite and the past participle, while German, Dutch, and English favor a common vowel for both forms. In change from the strong to the weak conjugation in Swedish, the preterite is more resistant than the past participle, while in the other languages it is the reverse. We provide a unified explanation for these facts based on differences in category frequency due to the prominence or lack of an aspectual distinction between preterite and perfect.*
SLS/BIALL Academic Law Library Survey 2008/2009
Authors: Clinch Peter
Published: December 2010

This is the latest report analysing the results of the Society of Legal Scholars and BIALL Survey. It has been written by Peter Clinch, Senior Subject Librarian for Law, Cardiff University.
Extra Costs for Urban Older People with Disabilities in Northern China
Authors: Wang Xiaolin , Xu Liping , Shang Xiaoyuan , Guo Ping
Published: December 2010

This paper uses the living standards method to estimate the extra costs for older people with functional disabilities in urban areas in Northern China. The research finds that the cost for older people who live alone is higher than those who live with other family members, and their living standard is lower. The costs increase with the age, especially for the oldest old people who live alone. The cost for older women is higher than their male counterparts. The extra costs of support for people with functional disabilities decrease the overall living standard of the household.
Value Performance
Authors: Schönborn Gregor
Published: December 2010

In spite of a considerable body of literature, the relations between aspects of corporate culture and corporate success are not clear. This is due to the complexity and inconsistency concerning corporate culture and success. Most studies tend to focus on codified norms but less on implicit assumptions and values according to Schein (1990 , 2009 ), and on positive but not negative cultural impacts. The research situation implies that managers do not pay enough attention to cultural issues. The success relation was investigated in an explorative study using a weighted sample of 2,873 persons from 46 German companies who participated in an online questionnaire designed to cover all levels of corporate culture. The impact of explorative analyzed corporate culture’s construct to success was assessed by correlations and regressions. Results indicate that corporate responsibility with respect to external stakeholders as well as to employees, accompanied by participative leadership, are crucial cultural conditions for corporate success.
Dopamine Transporter in vitro Binding and in vivo Imaging in the Brain
Authors: Bergström Kim A. , Tupala Erkki , Tiihonen Jari
Published: December 2010

Abstract: Much research interest has lately been focused on the dopamine transporter function in brain. Recent findings indicate that dopamine reuptake is more like a highly regulated than a constitutive determinant of dopamine clearance. Positron emission tomography (PET) and single‐photon emission tomography (SPET) offer unique methods to study dopamine transporter function. Results from in vivo PET and SPET studies correspond well with in vitro studies performed on post mortem human brain tissue. Considering some of the variances between in vitro and in vivo receptor binding phenomena it may be that the role of a compound to alter binding to monoamine uptake sites in vitro does not indicate its potential to affect monoamine transporters after administration in vivo. This discrepancy may be better understood taking into account recent studies indicating the possibility of a rapid regulation of transporter function and surface expression. Furthermore, the dopamine transporter is a fruitful target for CNS drug discovery. Fundamental nature of drug actions in vivo may be studied using demonstrated in vitro and in vivo imaging methods.
Inhibition of MAO‐A Activity Enhances Behavioural Activity of Rats Assessed Using Water Maze and Open Arena Tasks
Authors: Barbelivien Alexandra , Nyman Leena , Haapalinna Antti , Sirviö Jouni
Published: December 2010

Abstract: To determine if the inhibition of MAO‐A and/or MAO‐B activities can influence cognitive processes in adult rats, we analysed whether chronic treatment with clorgyline, l‐deprenyl and pargyline could modify the performance of adult rats in a modified version of the water maze task. The effects of these treatments on locomotor activity and enzyme activities were also assessed. Rats were treated for 24 days with clorgyline (0.2 mg/kg), l‐deprenyl (0.25 mg/kg) and pargyline (1 or 10 mg/kg). The treatments were started two weeks before the water maze experiment and continued until the end of testing. The rats were trained to find a submerged platform (6 days:1 trial/day; 7 th day: probe trial). Over the next three days, locomotor activity was assessed in an open arena. Treatments with clorgyline (MAO‐A inhibitor), l‐deprenyl (MAO‐B inhibitor) and pargyline (non‐selective MAO inhibitor) did not improve the finding of the hidden platform, when compared to treatment with saline, but significantly increased the swimming speed of the rats. The different treatments, when compared to saline, failed to modify the distance covered and the number of groomings performed in the open arena. However, clorgyline and pargyline, 10 mg/kg, increased the number of faecal boli and clorgyline enhanced the number of rearings made when compared to saline, l‐deprenyl and pargyline, 10 mg/kg. These results indicate that near total inhibition of MAO‐A by clorgyline and pargyline as assessed by MAO activity measurement induces an increase in locomotor activity but that inhibition of MAO‐A or MAO‐B, either alone or combined, does not facilitate spatial learning in adult rats.
in vivo 3D Morphology of Astrocyte—Vasculature Interactions in the Somatosensory Cortex: Implications for Neurovascular Coupling
Authors: McCaslin Addason F H , Chen Brenda R , Radosevich Andrew J , Cauli Bruno , Hillman Elizabeth M C
Published: December 2010

Astrocytes are increasingly believed to play an important role in neurovascular coupling. Recent in vivo studies have shown that intracellular calcium levels in astrocytes correlate with reactivity in adjacent diving arterioles. However, the hemodynamic response to stimulation involves a complex orchestration of vessel dilations and constrictions that spread rapidly over wide distances. In this work, we study the three-dimensional cytoarchitecture of astrocytes and their interrelations with blood vessels down through layer IV of the mouse somatosensory cortex using in vivo two-photon microscopy. Vessels and astrocytes were visualized through intravenous dextran-conjugated fluorescein and cortically applied sulforhodamine 101 (SR101), respectively. In addition to exploring astrocyte density, vascular proximity, and microvascular density, we found that sheathing of subpial vessels by astrocyte processes was continuous along all capillaries, arterioles, and veins, comprising a highly interconnected pathway through which signals could feasibly be relayed over long distances via gap junctions. An inner SR101-positive sheath noted along pial and diving arterioles was determined to be nonastrocytic, and appears to represent selective SR101 staining of arterial endothelial cells. Our findings underscore the intimate relationship between astrocytes and all cortical blood vessels, and suggest that astrocytes could influence neurovascular regulation at a range of sites, including the capillary bed and pial arterioles.
The effect of laser wavelength on emission and particle dynamics of Sn plasma
Authors: Campos D. , Harilal S. S. , Hassanein A.
Published: December 2010

We investigated the effects of laser wavelength on the atomic, ionic, and radiative emission from laser-produced tin plasmas. For generating plasmas, planar tin targets were excited using either high intensity neodymium-doped yttrium aluminum garnet (Nd:YAG, 1.06 μm) or carbon dioxide (CO2, 10.6 μm) laser pulses; both are considered to be potential excitation lasers for an extreme ultraviolet (EUV) lithography laser-produced plasma light source. Various diagnostic tools were utilized for investigating ionic, neutral, and radiative emission from Sn plasmas including Faraday cup, witness plate in conjunction with x-ray photoelectron spectroscopy (XPS), EUV, and visible emission spectroscopy and photography. Atomic and ionic analysis showed that the amount of debris emitted by the Nd:YAG generated plasmas was considerably higher than the CO2 laser-produced plasmas. The angular distributions of both atomic and ionic debris were found to be more forward-centric for the 1.06 μm generated plasma while being much more uniform for the 10.6 μm heated plasma. EUV and visible emission images of the plasma also showed a forward-centric appearance for 1.06 μm heated plasmas. The strength of excited neutral emission was considerably lower for the case of the 10.6 μm plasma while the kinetic energies of ions debris were found to be much higher for CO2 generated plasmas. Surface analysis of the craters created by the lasers showed that the mass ablation rate is 3.6 times higher for Nd:YAG laser generated plasmas compared to CO2 generated plasmas at maximum EUV emission.
Focus on the electrical field-induced strain of electroactive polymers and the observed saturation
Authors: Guyomar D. , Yuse K. , Cottinet P.-J. , Kanda M. , Lebrun L.
Published: December 2010

Thanks to their large electrical field-induced strains, electroactive polymers can be used in various applications; as electroactive materials for artificial muscles or as active materials of membranes, due to their flexibility. One drawback concerning their use involves the saturation of the electrical field-induced strain which occurs at around 20% for a polymer film with a thickness of 80 μm. Few studies have been devoted to the understanding of this saturation. To this end, the present paper describes mechanical measurements of the extensive strain versus stress and the determination of the current flowing through an electroactive polymer driven by an electrical field. These experiments have clearly demonstrated that the observed saturation of the electrical induced strain was not due to a mechanical saturation within the sample but to the saturation of the electrically induced polarization. By carrying out a suitable modeling of the polarization versus electrical field, it was possible to calculate the strain and current versus electrical field. These values were then compared to experimental data, and were found to show a very good agreement.
Phase-field simulation for crystallization of a highly supercooled forsterite-chondrule melt droplet
Authors: Miura Hitoshi , Yokoyama Etsuro , Nagashima Ken , Tsukamoto Katsuo , Srivastava Atul
Published: December 2010

Chondrules are submillimeter-sized and spherical-shaped crystalline grains consisting mainly of silicate material observed in chondritic meteorites. We numerically simulated pattern formation of a forsterite (Mg2SiO4)-chondrule in the melt droplet using a phase-field method. Because of the large surface-to-volume ratio, the surface cooling term was introduced in the framework of this method. We reproduced an unique crystal growth pattern inside the droplet composed of two distinguishable parts; the rim that covers whole droplet surface, and dendrite inside the droplet. It was found that the rim was formed when there is a large temperature difference of ∼100 K between the center and surface of the droplet due to the large cooling flux at the surface. In order to obtain the temperature difference, we derived temperature distribution of the droplet analytically, and concluded that the rim was formed only when the droplet cools rapidly at a rate of Rcool∼103 K s−1. However, when the surface cooling was so large as the temperature at the droplet center still remains above the melting point, no dendrite was obtained, though the rim was formed. The double structure captures the distinctive features of barred-olivine textures observed in natural chondrules.
Numerical simulation of free evolution in solid-state nuclear magnetic resonance using low-order correlations in Liouville space
Authors: Dumez Jean-Nicolas , Butler Mark C. , Emsley Lyndon
Published: December 2010

The design of simulations of free evolution in dipolar-coupled nuclear-spin systems using low-order correlations in Liouville space (LCL) is discussed, and a computational scheme relying on the Suzuki–Trotter algorithm and involving minimal memory requirements is described. The unusual nature of the approximation introduced by Liouville-space reduction in a spinning solid is highlighted by considering the accuracy of LCL simulations at different spinning frequencies, the quasiequilibria achieved by spin systems in LCL simulations, and the growth of high-order coherences in the exact dynamics. In particular, it is shown that accurate LCL simulations of proton spin diffusion occur in a regime where the reduced space excludes the coherences that make the dominant contribution to \documentclass[12pt]{minimal}\begin{document}$\Vert \sigma \Vert ^2$\end{document}∥σ∥2, the norm-squared of the density matrix.
Liquid crystal device with 50 nm nanogroove structure fabricated by nanoimprint lithography
Authors: Takahashi Hayato , Sakamoto Takumi , Okada Hiroyuki
Published: December 2010

We have investigated the alignment of nematic liquid crystals (NLCs) using 50 nm ultrafine nanogrooves fabricated by electron-beam (EB) lithography and nanoimprint lithography. To improve the wettability of NLCs, silicon dioxide was sputtered onto the NLCs after nanogroove fabrication. The azimuthal and polar anchoring energies obtained were 9.4×10−5 J/m2 and 3.6×10−4 J/m2, respectively. From the electro-optical characteristic of a twisted nematic (TN) liquid crystal (LC) cell, the contrast ratio of the TN cell was found to be 44:1, which is a relatively low value because of the misalignment of the EB exposure. However, a steeper and common threshold voltage was obtained for the TN LC cell.
Effect of annealing and Nd concentration on the photoluminescence of Nd3+ ions coupled with silicon nanoparticles
Authors: Debieu O. , Bréard D. , Podhorodecki A. , Zatryb G. , Misiewicz J. , Labbé C. , Cardin J. , Gourbilleau F.
Published: December 2010

We report on the microstructure and photoluminescence (PL) properties of Nd-doped SiO2 thin films containing silicon nanoparticles (Si-np) as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing due to the agglomeration of the Si excess resulting in the formation of Si-np. Besides, after annealing, the films exhibit PL from excitonic states confined in Si-np. We showed that the intensity of the PL of Nd3+ ions that occurs at ∼0.92, 1.06, and 1.4 μm is maximal at low Nd concentration and while well-passivated Si-np are formed. FTIR and x-ray measurements showed that the increase in the Nd incorporation has detrimental effects on the PL of Nd3+ because of the formation of Nd2O3 nanocrystals and inherent disorder in the SiO2 host matrix. PL excitation measurements demonstrate that the PL of Nd3+ ions is nonresonant and follows the excitation of Si-np giving new evidence of the energy transfer from Si-np toward the rare earth ions.
Phase behavior of polydisperse spheres: Simulation strategies and an application to the freezing transition
Authors: Wilding Nigel B. , Sollich Peter
Published: December 2010

The statistical mechanics of phase transitions in dense systems of polydisperse particles presents distinctive challenges to computer simulation and analytical theory alike. The core difficulty, namely, dealing correctly with particle size fractionation between coexisting phases, is set out in the context of a critique of previous simulation work on such systems. Specialized Monte Carlo simulation techniques and moment free energy method calculations, capable of treating fractionation exactly, are then described and deployed to study the fluid–solid transition of an assembly of repulsive spherical particles described by a top-hat “parent” distribution of particle sizes. The cloud curve delineating the solid–fluid coexistence region is mapped as a function of the degree of polydispersity δ, and the properties of the incipient “shadow” phases are presented. The coexistence region is found to shift to higher densities as δ increases, but does not exhibit the sharp narrowing predicted by many theories and some simulations.
Translational diffusion of cumene and 3-methylpentane on free surfaces and pore walls studied by time-of-flight secondary ion mass spectrometry
Authors: Souda Ryutaro
Published: December 2010

Mobility of molecules in confined geometry has been studied extensively, but the origins of finite size effects on reduction of the glass transition temperature, Tg, are controversial especially for supported thin films. We investigate uptake of probe molecules in vapor-deposited thin films of cumene, 3-methylpentane, and heavy water using secondary ion mass spectrometry and discuss roles of individual molecular motion during structural relaxation and glass–liquid transition. The surface mobility is found to be enhanced for low-density glasses in the sub-Tg region because of the diffusion of molecules on pore walls, resulting in densification of a film via pore collapse. Even for high-density glasses without pores, self-diffusion commences prior to the film morphology change at Tg, which is thought to be related to decoupling between translational diffusivity and viscosity. The diffusivity of deeply supercooled liquid tends to be enhanced when it is confined in pores of amorphous solid water. The diffusivity of molecules is further enhanced at temperatures higher than 1.2–1.3 Tg irrespective of the confinement.
Chiral symmetry breaking in a microscopic model with asymmetric autocatalysis and inhibition
Authors: Hatch Harold W. , Stillinger Frank H. , Debenedetti Pablo G.
Published: December 2010

Asymmetric autocatalysis and inhibition have been proposed as key processes in the spontaneous emergence of chiral symmetry breaking in a prebiotic world. An elementary lattice model is formulated to simulate the kinetics of chiral symmetry breaking via autocatalysis and inhibition in a mixture of prochiral reactants, chiral products, and inert solvent. Starting from a chirally unbiased initial state, spontaneous symmetry breaking occurs in spite of equal a priori probability for creating either product enantiomer, and the coupled reaction–diffusion processes subsequently amplify the random early-stage symmetry breaking. The processes of reaction and diffusion are kinetically intertwined in a way leading to competition in the appearance of enantiomeric excess. An effective transition temperature can be identified below which spontaneous symmetry breaking appears. In the absence of inhibition, reactions are predominantly autocatalytic under both reaction control (fast diffusion, slow reaction) or diffusion control (fast reaction, slow diffusion) conditions. In the presence of inhibition, simulations with different system sizes converge to the same transition temperature under reaction control conditions, and in this limit the reactions are predominantly nonautocatalytic.
Low O2 dissociation barrier on Pt(111) due to adsorbate–adsorbate interactions
Authors: Miller D. J. , Öberg H. , Näslund L.-Å. , Anniyev T. , Ogasawara H. , Pettersson L. G. M. , Nilsson A.
Published: December 2010

O2 dissociation on Pt(111) has been followed at low and saturation coverage using temperature-programmed x-ray photoelectron spectroscopy and simulated with mean-field kinetic modeling, yielding dissociation (Ea) and desorption (Ed) barriers of 0.32 and 0.36 eV, respectively. Density functional theory calculations show that Ea is strongly influenced by the O–O interatomic potential in the atomic final state: of the supercells considered, that which maximizes attractive third-nearest-neighbor interactions in the atomic final state yields both the lowest computed dissociation barrier (0.24 eV) and the best agreement with experiment. It is proposed that the effect of adsorbate–adsorbate interactions must be considered when modeling catalytic processes involving dissociative steps.
Adsorption configuration effects on the surface diffusion of large organic molecules: The case of Violet Lander
Authors: Sato F. , Legoas S. B. , Otero R. , Hümmelink F. , Thostrup P. , Lægsgaard E. , Stensgaard I. , Besenbacher F. , Galvão D. S.
Published: December 2010

Violet Lander (C \documentclass[12pt]{minimal}\begin{document}$_{108}$\end{document}108H \documentclass[12pt]{minimal}\begin{document}$_{104}$\end{document}104) is a large organic molecule that when deposited on Cu(110) surface exhibits lock-and-key like behavior [Otero et al., Nature Mater. 3, 779 (2004)]. In this work, we report a detailed fully atomistic molecular mechanics and molecular dynamics study of this phenomenon. Our results show that it has its physical basis on the interplay of the molecular hydrogens and the Cu(110) atomic spacing, which is a direct consequence of the matching between molecule and surface dimensions. This information could be used to find new molecules capable of displaying lock-and-key behavior with new potential applications in nanotechnology.
Crystal structure prediction using the minima hopping method
Authors: Amsler Maximilian , Goedecker Stefan
Published: December 2010

A structure prediction method is presented based on the minima hopping method. To escape local minima, moves on the configurational enthalpy surface are performed by variable cell shape molecular dynamics. To optimize the escape steps the initial atomic and cell velocities are aligned to low curvature directions of the current local minimum. The method is applied to both silicon crystals and well-studied binary Lennard-Jones mixtures. For the latter new putative ground state structures are presented. It is shown that a high success rate is achieved and a reliable prediction of unknown ground state structures is possible.
Enhanced room temperature oxidation in silicon and porous silicon under 10 keV x-ray irradiation
Authors: Ryckman Judson D. , Reed Robert A. , Weller Robert A. , Fleetwood D. M. , Weiss S. M.
Published: December 2010

We report the observation of enhanced oxidation on silicon and porous silicon samples exposed in air ambient to high-dose-rate 10 keV x-ray radiation at room temperature. The evolution of the radiation-induced oxide growth is monitored by ellipsometry and interferometric reflectance spectroscopy. Fourier transform infrared (FTIR) spectroscopy shows the emergence of Si–O–Si stretching modes and corresponding suppression of SiHx and Si–Si modes in the porous silicon samples. The radiation response depends strongly on initial native oxide thickness and Si–H surface species. The enhanced oxidation mechanism is attributed to photoinduced oxidation processes wherein energetic photons are used to dissociate molecular oxygen and promote the formation of more reactive oxygen species.
Energy dissipation in microfluidic beam resonators: Dependence on mode number
Authors: Sader John E. , Lee Jungchul , Manalis Scott R.
Published: December 2010

Energy dissipation experienced by vibrating microcantilever beams immersed in fluid is strongly dependent on the mode of vibration, with quality factors typically increasing with mode number. Recently, we examined energy dissipation in a new class of cantilever device that embeds a microfluidic channel in its interior—the fundamental mode of vibration only was considered. Due to its importance in practice, we examine the effect of mode number on energy dissipation in these microfluidic beam resonators. Interestingly, and in contrast to other cantilever devices, we find that the quality factor typically decreases with increasing mode number. We explore the underlying physical mechanisms leading to this counterintuitive behavior, and provide a detailed comparison to experimental measurements for which good agreement is found.
A probabilistic approach to some results by Nieto and Truax
Authors: Vignat C.
Published: December 2010

It is shown that the usual operational methods applied to characterize the properties of Gould and Hopper polynomials, as well as the properties of quantum higher-order and squeezed states, can be replaced by a probabilistic approach using stable distributions.
Equilibrium strain and dislocation density in exponentially graded Si1−xGex/Si (001)
Authors: Bertoli B. , Sidoti D. , Xhurxhi S. , Kujofsa T. , Cheruku S. , Correa J. P. , Rago P. B. , Suarez E. N. , Jain F. C. , Ayers J. E.
Published: December 2010

We have calculated the equilibrium strain and misfit dislocation density profiles for heteroepitaxial Si1−xGex/Si (001) with convex exponential grading of composition. A graded layer of this type exhibits two regions free from misfit dislocations, one near the interface of thickness y1 and another near the free surface of thickness h−yd, where h is the layer thickness. The intermediate region contains an exponentially tapered density of misfit dislocations. We report approximate analytical models for the strain and dislocation density profile in exponentially graded Si1−xGex/Si (001) which may be used to calculate the effective stress and rate of lattice relaxation. The results of this work are readily extended to other semiconductor material systems and may be applied to the design of exponentially graded buffer layers for metamorphic device structures including transistors and light emitting diodes.
Parametric analysis of a coupled photovoltaic/thermal concentrating solar collector for electricity generation
Authors: Otanicar Todd , Chowdhury Ihtesham , Phelan Patrick E. , Prasher Ravi
Published: December 2010

The analysis of the combined efficiencies in a coupled photovoltaic (PV)/thermal concentrating solar collector are presented based on a coupled electrical/thermal model. The calculations take into account the drop in efficiency that accompanies the operation of PV cells at elevated temperatures along with a detailed analysis of the thermal system including losses. An iterative numerical scheme is described that involves a coupled electrothermal simulation of the solar energy conversion process. In the proposed configuration losses in the PV cell due to reduced efficiencies at elevated temperatures and the incident solar energy below the PV bandgap are both harnessed as heat. This thermal energy is then used to drive a thermodynamic power cycle. The simulations show that it is possible to optimize the overall efficiency of the system by variation in key factors such as the solar concentration factor, the band gap of the PV material, and the system thermal design configuration, leading to a maximum combined efficiency of ∼32.3% for solar concentrations between 10–50 and a band-gap around 1.5–2.0 eV.
Why quantum engineering?
Authors: Zagoskin A. M.
Published: December 2010

Progress in experimental techniques and theoretical modeling has made it possible to fabricate and test macroscopic structures which use quantum coherent solid state qubits as building blocks. The results of this quantum engineering are likely to go far beyond the limited goals of quantum computing and quantum communication and may provide a direct way to explore the quantum-classical boundary. Some recent developments are discussed.
Nonadiabatic Josephson dynamics in junctions with in-gap quasiparticles
Authors: Michelsen J. , Shumeiko V. S.
Published: December 2010

Conventional models of Josephson junction dynamics rely on the absence of low-energy quasiparticle states owing to a large superconducting gap. With this assumption the quasiparticle degrees of freedom are ⟪frozen out⟫ and the phase difference becomes the only free variable, acting as a fictitious particle in a temporally localized Josephson potential related to the adiabatic and nondissipative supercurrent across the junction. In this article we develop a general framework to incorporate the effects of low-energy quasiparticles interacting nonadiabatically with the phase degree of freedom. These quasiparticle states typically exist in constriction type junctions with high transparency channels or resonant states, as well as in junctions of unconventional superconductors. Recent experiments have also revealed the existence of spurious low-energy in-gap states in tunnel junctions of conventional superconductors—a system for which the adiabatic assumption is typically assumed to be valid. We show that a resonant interaction with these low-energy states, rather than the Josephson potential, determines the nonlinear Josephson dynamics at small amplitudes.
Highly efficient white organic light-emitting diodes based on fluorescent blue emitters
Authors: Rosenow Thomas C. , Furno Mauro , Reineke Sebastian , Olthof Selina , Lüssem Björn , Leo Karl
Published: December 2010

Beside inorganic LEDs and fluorescent lamps, organic light-emitting diodes (OLEDs) are evolving into a serious alternative to incandescent lamps. Up to now, it was assumed that all-phosphorescent OLEDs are required for reaching sufficiently high efficiencies. However, the stability of phosphorescent blue emitters is a major challenge. We present a novel approach to achieve highly efficient (up to 90 lm/W at 1000 cd/m2 using a macroextractor) white light emission from OLEDs. The here presented combination of a fluorescent blue and a phosphorescent red emitter simultaneously allows for a strong blue emission and efficient triplet transfer to the phosphor. The spectrum is extended in the green and yellow region by a full phosphorescent unit stacked on top of the triplet harvesting device. This superposition of four different emitters results in color coordinates close to illuminant A and a color rendering index of 80. Furthermore, color stability is given with respect to varying driving conditions and estimations of the electrical and optical efficiencies are provided.