bluuebunny/crossref_metadata_2025 huggingface dataset:
Intracerebroventricular ouabain administration induces oxidative stress in the rat brain
Authors: Riegel Rafael E. , Valvassori Samira S. , Moretti Morgana , Ferreira Camila L. , Steckert Amanda V. , de Souza Bruna , Dal‐Pizzol Felipe , Quevedo João
Published: February 2010

Intracerebroventricular (ICV) injection of ouabain (a potent Na+/K+‐ATPase inhibitor) in rats resulted in manic‐like effects. There is an emerging body of data indicating that major neuropsychiatric disorders, such as bipolar disorder and schizophrenia, are associated with increased oxidative stress. In this study, we investigated the effects of ICV ouabain injection on oxidative stress parameters in total tissue of rat brain. Our findings demonstrated that ICV injection increased thiobarbituric acid reactive species levels and protein carbonyl generation in the prefrontal cortex and hippocampus of rats. Moreover, the activity of the antioxidants enzymes catalase and superoxide dismutase was altered in several areas of the rat brain and cerebrospinal fluid of ICV ouabain‐subjected rats. These results showed that Na+/K+‐ATPase inhibition can lead to oxidative stress in the brain of rats.
Anal dilation during labor
Authors: Kalis Vladimir , Karbanova Jaroslava , Bukacova Zuzana , Bednarova Barbora , Rokyta Zdenek , Kralickova Milena
Published: February 2010

Objective

To determine the incidence and range of anal dilation during the final phase of the second stage of labor and shortly after delivery; determine whether parity affects anal dilation; and obtain anthropometric data for future projects.

Methods

The anal diameter was measured on admission, when the fetal head crowned, and after suturing perineal injury in 142 women delivered between August 2008 and May 2009 at University Hospital Pilsen and District Hospital Klatovy, in the Czech Republic.

Results

The anus was dilated during the second stage of labor in all women, and differences between primiparas and multiparas were not significant. The medians for both the anteroposterior and transverse diameters were 25 mm. No measured variable was statistically associated with anal sphincter dilation.

Conclusion

Anal dilation during the second stage of labor causes anthropometric changes to the perineum. This ought to be considered when designing anthropometric studies and in studies aiming at minimizing anal sphincter trauma during delivery.
Evaluation of cervical visual inspection screening in Dar es Salaam, Tanzania
Authors: Ngoma Twalib , Muwonge Richard , Mwaiselage Julius , Kawegere Jesca , Bukori Pendo , Sankaranarayanan Rengaswamy
Published: February 2010

Objective

To evaluate the feasibility and performance of screening for cervical cancer using visual inspection with acetic acid (VIA) or with Lugol's iodine (VILI) in Dar es Salaam, Tanzania.

Methods

The accuracy of tests for detecting cervical intraepithelial neoplasia (CIN) was assessed in a cross‐sectional study of 10 378 women. All women who were screened underwent colposcopy, and biopsies were offered to those with abnormal colposcopy results.

Results

The positivity rates were 3.8% for VIA and 4.8% for VILI. The peak positivity rates for both visual tests were observed just after training or re‐training and gradually declined thereafter. CIN 1 was diagnosed in 41 women, CIN 2–3 in 33 women, and invasive cancer in 200 women, showing high detection rates of invasive cancer. The sensitivity and specificity for the detection of CIN 2–3 lesions were 60.6% (95% confidence interval [CI], 42.1–77.1) and 98.2% (95% CI, 97.9–98.4), respectively, for VIA; and 93.9% (95% CI, 79.8–99.3) and 97.3% (95% CI, 97.0–97.6), respectively, for VILI. Two‐thirds of the women detected with CIN 2–3 lesions were treated.

Conclusion

Both visual screening tests are useful and accurate, especially in low‐income settings. Standardization of assessment of the visual inspection techniques, continual training and supervision, and quality control measures are important for successful visual screening programs.
Fertility and obstetric outcome after conservative management of placenta accreta
Authors: Provansal Magali , Courbiere Blandine , Agostini Aubert , D'Ercole Claude , Boubli Léon , Bretelle Florence
Published: February 2010

Objective

To determine the fertility and obstetric outcomes after conservative management of placenta accreta.

Methods

A retrospective observational cohort study of all identified cases of placenta accreta from 1993 to 2007 in 2 tertiary university hospitals in France. For patients treated conservatively, maternal and fetal morbidity, reproductive function, fertility, and subsequent pregnancies were recorded.

Results

During the study period, 46 patients were treated by conservative management; 6 patients underwent a secondary hysterectomy. Of the remaining 40 patients, 35 were followed up for a median of 65 months (range 18–156 months). Patients resumed their menstrual cycles after a median of 130 days (range 48–176 days). Menses were irregular in 11 patients (31%), but none had amenorrhea. Twelve of the 14 patients desiring another pregnancy achieved a total of 15 pregnancies; 2 patients had recurrent placenta accreta. Five spontaneous abortions and 1 termination of pregnancy occurred during the first trimester. The median term at delivery was 37 weeks (range, 35–40 weeks). Four patients delivered prematurely.

Conclusion

Conservative management of placenta accreta can preserve fertility, although the risk of recurrent placenta accreta appears to be high.
Functional testing of a tissue‐engineered vocal fold cover replacement
Authors: Long Jennifer L. , Neubauer Juergen , Zhang Zhaoyan , Zuk Patricia , Berke Gerald S. , Chhetri Dinesh K.
Published: February 2010

Objectives

Tissue engineering may provide a treatment for severe vocal fold scars. This study quantifies mechanical properties and demonstrates vibration of a tissue‐engineered vocal fold cover replacement.

Methods

Tissue‐engineered constructs were produced from fibrin and adipose‐derived stem cells. Optimized bilayered constructs contained epithelial and mesenchymal cell phenotypes in a stratified geometry. For comparison, homogeneous constructs did not have epithelial differentiation. Elastic modulus was determined using indentation. Immunohistochemical labeling for type I collagen was performed. A bilayered construct was also tested in phonation in an excised larynx model.

Results

Bilayered vocal fold cover replacements had indentation moduli similar to human vocal fold covers (mean construct modulus 6.8 kPa). Collagen deposition occurred in the middle of the construct. Homogeneous constructs had a mean modulus of 8.3 kPa, and collagen was concentrated at the surface. An excised larynx with unilateral vocal fold cover replacement phonated and exhibited mucosal waves at physiologic airflow.

Conclusion

Bilayered tissue‐engineered constructs were produced that exhibited indentation modulus, microstructure, and vibration similar to that exhibited by human vocal fold covers.
Preoperative predictors of incudal necrosis in chronic suppurative otitis media
Authors: Ebenezer Jareen , Rupa Vedantam
Published: February 2010

Objective

To determine the predictive value of preoperative clinical, audiological, and radiological factors in diagnosing incudal necrosis in patients with tubotympanic chronic suppurative otitis media (CSOM).

Study Design

Case series with planned data collection.

Setting

Tertiary care referral center.

Subjects and Methods

Patients older than five years of age diagnosed with tubotympanic CSOM who underwent tympanomastoid surgery were recruited. Findings on otoscopy, x‐ray mastoid, pure‐tone audiometry, and intraoperative otomicroscopy were recorded.

Results

Incus necrosis occurred in 24 (16%) of a total of 150 patients. On bivariate analysis, findings of active ear discharge (P = 0.01), anterosuperior location of perforation (P = 0.03), exposure of incudostapedial joint (P = 0.05), edematous middle ear mucous membrane (P = 0.05), middle ear granulations (P = 0.004), foreshortening of the handle of malleus (P = 0.04), moderate to moderately severe hearing loss (41‐70 dB HL) (P = 0.000), and air‐bone gap > 40 dB (P = 0.001) were found to be associated with incus necrosis. Intraoperative findings of aditus block (P = 0.001) and mastoid granulations (P = 0.005) were also found to be significantly associated with incus necrosis. Mastoid pneumatization and perforation size and site were not associated with incus necrosis. On multivariate analysis, only middle ear granulations (P = 0.04; odds ratio [OR] 3.161; 95% confidence interval [95% CI] 1.087‐9.196) and a moderate to moderately severe hearing loss (41‐70 dB HL) (P = 0.03; OR 1.720; CI 1.064‐2.782) were found to be significant risk factors.

Conclusion

Incus necrosis is best predicted by the presence of middle ear granulations and moderate to moderately severe hearing loss (41‐70 dB HL). Knowledge of this information preoperatively can influence surgical decision making and preparedness regarding ossiculoplasty and patient consent.
Janus flap: Bilateral nasoseptal flaps for anterior skull base reconstruction
Authors: Nyquist Gurston G. , Anand Vijay K. , Singh Ameet , Schwartz Theodore H.
Published: February 2010

Objective

Large dural defects after extended endoscopic endonasal skull base resections require meticulous reconstruction to prevent a cerebrospinal fluid leak postoperatively. The nasoseptal flap is a vascularized tissue graft developed to aid in the multilayer reconstruction of the skull base. The purpose of this study is to describe the first experiences with bilateral nasoseptal flaps for reconstruction of very large skull base defects.

Study Design

Prospective, observational study.

Setting

Large tertiary referral center (New York Presbyterian Hospital).

Subjects and Methods

Five patients underwent a multilayer reconstruction after an extended endoscopic transsphenoidal skull base surgery that included bilateral nasoseptal flaps. Pathologies consisted of two pituitary macroadenomas, one planum sphenoidale meningioma, one craniopharyngioma, and one cavernous sinus hemangioma.

Results

All five patients underwent successful skull base reconstruction without a cerebrospinal fluid leak, complication at the reconstruction site, or anterior extension of the posterior septal perforation.

Conclusion

Bilateral nasoseptal flaps are a viable option for large dural defects of the anterior and ventral skull base when one nasoseptal flap may not completely seal the entire defect.
Portfolio Optimization with Mental Accounts
Authors: Das Sanjiv , Markowitz Harry , Scheid Jonathan , Statman Meir
Published: February 2010

We integrate appealing features of Markowitz’s mean-variance portfolio theory (MVT) and Shefrin and Statman’s behavioral portfolio theory (BPT) into a new mental accounting (MA) framework. Features of the MA framework include an MA structure of portfolios, a definition of risk as the probability of failing to reach the threshold level in each mental account, and attitudes toward risk that vary by account. We demonstrate a mathematical equivalence between MVT, MA, and risk management using value at risk (VaR). The aggregate allocation across MA subportfolios is mean-variance efficient with short selling. Short-selling constraints on mental accounts impose very minor reductions in certainty equivalents, only if binding for the aggregate portfolio, offsetting utility losses from errors in specifying risk-aversion coefficients in MVT applications. These generalizations of MVT and BPT via a unified MA framework result in a fruitful connection between investor consumption goals and portfolio production.
Measuring executive dysfunction in an acute rehabilitation setting: Using the dysexecutive questionnaire (DEX)
Authors: BENNETT PAULEEN C. , ONG BEN , PONSFORD JENNIE
Published: February 2010

It is recognized that existing neuropsychological measures of executive dysfunction lack adequate sensitivity and selectivity. While attempts have been made to develop improved measures, these have not yet been of great value to those who need to accurately identify executive deficits in a clinical setting. Several behavioral rating scales have been developed for this reason, including the 20-item Dysexecutive Questionnaire (DEX), which forms part of the Behavioral Assessment of the Dysexecutive Syndrome (BADS) test battery. To investigate the ability of the DEX to identify executive dysfunction in an acute rehabilitation setting, the BADS was administered to 64 persons who had sustained traumatic brain injury. It was found to be almost as sensitive to executive dysfunction, as measured by the total score obtained on the BADS battery, as an extended 65-item version of the scale, when completed by either the occupational therapist or clinical neuropsychologist working with each patient. Family members and the patient themselves provided, as expected, less accurate information. Our results indicate that the DEX can be used with some confidence as a screening instrument to identify executive dysfunction in an acute rehabilitation setting, provided it is completed by professional personnel, trained to be sensitive to the cognitive and behavioral concomitants of this disorder. (JINS, 2005,11, 376–385.)
Urban catalysts in theory and practice
Authors: Davis Juliet
Published: February 2010

This paper involves an analysis of the role of architectural projects which can be defined as ‘catalysts’ to urban renewal. The aims of this paper are twofold and the paper is divided accordingly into two main parts. The first aim is to discuss, with reference to the work of a number of urban and architectural thinkers, a range of ways in which the term ‘urban catalyst’ has been both conceptualised and applied. Discussion is structured in relation to the Oxford English Dictionary's definition of a ‘catalyst’ in the field of chemistry as,

[a] substance that when present in small amounts increases the rate of a chemical reaction or process but which is chemically unchanged by the reaction; a catalytic agent. (A substance which similarly slows down a reaction is occas. called a negative catalyst.)
The thickness of paint
Authors: Woolf Jonathan
Published: February 2010

A photograph by Robert Polidori, of a room within the city of Petra, shows a pristine cubic volume hewn out of the rock. The nature of the stone reveals different textural and figural qualities of the material when it becomes a floor, a wall or a ceiling. There is no need to ‘put’ the building together, to assemble it, because it is already exists. This, then, is the fantasy of the architect, to sculpt from a single substance that is both structure and surface, with the only remaining questions pertaining to shape and smoothness.
Fenofibrate Improves Cerebral Blood Flow after Middle Cerebral Artery Occlusion in Mice
Authors: Guo Qingmin , Wang Guangming , Namura Shobu
Published: February 2010

Correction to: Journal of Cerebral Blood Flow & Metabolism (2010) 30, 70–78; doi:10.1038/jcbfm.2009.185

Following the publication of this article, the authors noted an error in Figure 4. The hatched columns should indicate 100 mg/kg.
Hydrogel functionalization with DNA aptamers for sustained PDGF-BB release
Authors: Soontornworajit Boonchoy , Zhou Jing , Shaw Montgomery T. , Fan Tai-Hsi , Wang Yong
Published: February 2010

Hydrogel functionalization with DNA aptamers can be applied for developing a novel sustained-release system.
Rational design of a highly selective and sensitive fluorescent PET probe for discrimination of thiophenols and aliphatic thiols
Authors: Jiang Wei , Cao Yanting , Liu Yuan , Wang Wei
Published: February 2010

A novel highly sensitive and selective ‘off-on’ fluorescent probe for thiophenols has been developed by a PET mechanism through a rational design.
Effect of electron cyclotron resonance ion source frequency tuning on ion beam intensity and quality at Department of Physics, University of Jyväskylä
Authors: Toivanen V. , Koivisto H. , Steczkiewicz O. , Celona L. , Tarvainen O. , Ropponen T. , Gammino S. , Mascali D. , Ciavola G.
Published: February 2010

Ion beam intensity and quality have a crucial effect on the operation efficiency of the accelerator facilities. This paper presents the investigations on the ion beam intensity and quality after the mass separation performed with the Department of Physics, University of Jyväskylä 14 GHz electron cyclotron resonance ion source by sweeping the microwave in the 14.05–14.13 GHz range. In many cases a clear variation in the ion beam intensity and quality as a function of the frequency was observed. The effect of frequency tuning increased with the charge state. In addition, clear changes in the beam structure seen with the beam viewer were observed. The results confirmed that frequency tuning can have a remarkable effect on ion beam intensity and quality especially in the case of highly charged ion beams. The examples presented here represent the typical charge state behavior observed during the measurements.
The third generation superconducting 28 GHz electron cyclotron resonance ion source VENUS (invited)
Authors: Lyneis C. , Leitner D. , Leitner M. , Taylor C. , Abbott S.
Published: February 2010

VENUS is a third generation electron cyclotron resonance (ECR) ion source, which incorporates a high field superconducting NbTi magnet structure, a 28 GHz gryotron microwave source and a state of the art closed cycle cryosystem. During the decade from initial concept to regular operation, it has demonstrated both the feasibility and the performance levels of this new generation of ECR ion sources and required innovation on magnet construction, plasma chamber design, and beam transport. In this paper, the development, performance, and major innovations are described as well as a look to the potential to construct a fourth generation ECR ion source.
New development of advanced superconducting electron cyclotron resonance ion source SECRAL (invited)
Authors: Zhao H. W. , Sun L. T. , Lu W. , Zhang X. Z. , Guo X. H. , Cao Y. , Zhao H. Y. , Feng Y. C. , Li J. Y. , Ma H. Y. , Shang Y. , Ma B. H. , Wang H. , Li X. X. , Xie D. Z.
Published: February 2010

Superconducting electron cyclotron resonance ion source with advance design in Lanzhou (SECRAL) is an 18–28 GHz fully superconducting electron cyclotron resonance (ECR) ion source dedicated for highly charged heavy ion beam production. SECRAL, with an innovative superconducting magnet structure of solenoid-inside-sextupole and at lower frequency and lower rf power operation, may open a new way for developing compact and reliable high performance superconducting ECR ion source. One of the recent highlights achieved at SECRAL is that some new record beam currents for very high charge states were produced by 18 GHz or 18+14.5 GHz double frequency heating, such as 1 e μA of X129e43+, 22 e μA of B209i41+, and 1.5 e μA of B209i50+. To further enhance the performance of SECRAL, a 24 GHz/7 kW gyrotron microwave generator was installed and SECRAL was tested at 24 GHz. Some promising and exciting results at 24 GHz with new record highly charged ion beam intensities were produced, such as 455 e μA of X129e27+ and 152 e μA of X129e30+, although the commissioning time was limited within 3–4 weeks and rf power only 3–4 kW. Bremsstrahlung measurements at 24 GHz show that x-ray is much stronger with higher rf frequency, higher rf power. and higher minimum mirror magnetic field (minimum B). Preliminary emittance measurements indicate that SECRAL emittance at 24 GHz is slightly higher that at 18 GHz. SECRAL has been put into routine operation at 18 GHz for heavy ion research facility in Lanzhou (HIRFL) accelerator complex since May 2007. The total operation beam time from SECRAL for HIRFL accelerator has been more than 2000 h, and X129e27+, K78r19+, B209i31+, and N58i19+ beams were delivered. All of these new developments, the latest results, and long-term operation for the accelerator have again demonstrated that SECRAL is one of the best in the performance of ECR ion source for highly charged heavy ion beam production. Finally the future development of SECRAL will be presented.
Velocity measurements of inert porous materials driven by infrared-laser-ablated thin-film titanium
Authors: Bedeaux Brett C. , Trott Wayne M. , Castañeda Jaime N.
Published: February 2010

This article presents and interprets a series of experiments performed to measure the velocity of four inert low-density porous materials that were accelerated by an ablated thin-film titanium metal, created by vaporizing a 250-nm-thick layer of titanium with a high-energy, Q-switched, pulsed, and 1.054 μm neodymium-glass laser. Inert powder materials were chosen to match, among other characteristics, the morphology of energetic materials under consideration for use in detonator applications. The observed behavior occurs near the thin-film titanium ablation layer, through complex physical mechanisms, including laser absorption in the metal layer, ablation and formation of confined plasma that is a blackbody absorber of the remaining photon energy, and vaporization of the remaining titanium metal. One-dimensional hydrodynamic modeling provided a basis of comparison with the measured velocities. We found, as predicted in wave-propagation-code modeling, that an Asay foil can indicate total momentum of the driven material that is mechanically softer (lower in shock impedance) than the foil. The key conclusion is that the specific impulse delivered by the laser transfers a corresponding momentum to soft, organic power columns that are readily compacted. Impulse from the laser is less efficient in transferring momentum to hard inorganic particles that are less readily compacted.
Adhesion at diamond/metal interfaces: A density functional theory study
Authors: Guo Haibo , Qi Yue , Li Xiaodong
Published: February 2010

To understand the basic material properties required in selecting a metallic interlayer for enhanced adhesion of diamond coatings on the substrates, the interfaces between diamond and metals with different carbide formation enthalpies (Cu, Ti, and Al) are studied using density functional theory. It is found that the work of separation decreases, while the interface energy increases, with the carbide formation enthalpy ΔHf (Ti<Al<Cu). By comparing the work of separation at the interface with the work of decohesion of the metal, we found that the fracture is more likely to initiate in the metal phase near the interface; therefore a metal phase with a larger surface energy, γs (Ti>Cu>Al), is needed to achieve a higher overall interface strength. In addition, when the surface energy is larger than the interface energy, a wetted diamond/metal interface is formed during diamond nucleation, providing the strongest adhesion compared to other growth modes. These results indicate that a strong carbide-forming ability and a large surface energy of the interlayer promote nucleation and enhance the adhesion and interface strength of the coating/substrate system.
Exploring the mechanisms of H atom loss in simple azoles: Ultraviolet photolysis of pyrazole and triazole
Authors: King Graeme A. , Oliver Thomas A. A. , Nix Michael G. D. , Ashfold Michael N. R.
Published: February 2010

The photophysics of gas phase pyrazole (C3N2H4) and 2H-1,2,3-triazole (C2N3H3) molecules following excitation at wavelengths in the range 230 nm≥λphot≥193.3 nm has been investigated using the experimental technique of H (Rydberg) atom photofragment translational spectroscopy. The findings are compared with previous studies of pyrrole (C4N1H5) and imidazole (C3N2H4), providing a guide to H atom loss dynamics in simple N-containing heterocycles. CASPT2 theoretical methods have been employed to validate these findings. Photoexcitation of pyrazole at the longest wavelengths studied is deduced to involve π∗←π excitation, but photolysis at λphot≤214 nm is characterized by rapid N–H bond fission on a π1σ∗ potential energy surface. The eventual pyrazolyl radical products are formed in a range of vibrational levels associated with both the ground (A22) and first excited (B21) electronic states as a result of nonadiabatic coupling at large N–H bond lengths. The excitation energy of the lowest π1σ∗ state of pyrazole is found to be significantly higher in energy than that of pyrrole and imidazole. Similar studies of 2H-1,2,3-triazole reveal that the lowest π1σ∗ state is yet higher in energy and not accessible following excitation at λphot≥193.3 nm. The N–H bond strength of pyrazole is determined as 37 680±40 cm−1, significantly greater than that of the N–H bonds in pyrrole and imidazole. The correlation between the photochemistry of azoles and the number and position of nitrogen atoms within the ring framework is discussed in terms of molecular symmetry and orbital electron density. A photodissociation channel yielding H atoms with low kinetic energies is also clearly evident in both pyrazole and 2H-1,2,3-triazole. Companion studies of pyrazole-d1 suggest that these slow H atoms arise primarily from the N–H site, following π∗←π excitation, and subsequent internal conversion and/or unintended multiphoton absorption processes.
Experimental determination of band offsets at the SnS/CdS and SnS/InSxOy heterojunctions
Authors: Abdel Haleem A. M. , Ichimura M.
Published: February 2010

The semidirect x-ray photoelectron spectroscopy technique was used to measure the band alignments at the interface of heterostructures based on SnS. The layers were deposited by electrochemical deposition (ECD), chemical bath deposition (CBD), or photochemical deposition (PCD). The following four kinds of heterojunctions were characterized. (1) ECD-SnS/PCD-CdS. (2) CBD-SnS/PCD-CdS. (3) ECD-SnS/ECD-InSxOy. (4) CBD-SnS/ECD-InSxOy. The valence band offsets ΔEV of those four heterojunctions are determined to be 1.34, 1.59, 0.77, and 0.74±0.3 eV, respectively.
Low-profile embedded design of endfire scanning arrays with coordinate transformations
Authors: Kwon Do-Hoon , Emiroglu Caglar D.
Published: February 2010

Using the coordinate transformation approach, low-profile material-embedded horizontal linear arrays are designed such that the embedded arrays perform identically to a vertical array of the same length in free space. A vertical array in free space is first rotated by a right angle using a transformation-based rotator. The height of the rotated array is subsequently reduced through a reflectionless compression procedure in the vertical direction. The resulting low-profile array can scan a narrow beam at large scan angles without having a broadening main beam, unlike a linear array in free space. Two transformation material designs are presented based on circular and square annular rotators. Numerical simulation results are provided to verify the scanning performance. The effect of material loss on the radiation pattern is examined numerically.
A class of line-transformed cloaks with easily realizable constitutive parameters
Authors: Jiang Wei Xiang , Feng Ma Hui , Cheng Qiang , Cui Tie Jun
Published: February 2010

We consider a class of line-transformed cylindrical cloaks which have easily realizable constitutive parameters. The scattering properties of such cloaks have been investigated numerically for both transverse-electric and transverse-magnetic incidences of plane waves. A line-transformed invisibility cloak with a perfectly electric conducting (PEC) inner boundary is actually a reshaping of a PEC line to which the cloaked object is crushed. The numerical results of near-field distributions and far-field scattering properties have verified the above conclusions. We also investigate the relationship between the constitutive parameters of a line-transformed cloak and the length of the corresponding line. The changing range of constitutive parameters is large when the line is short, while the changing range becomes small when the line is long. The above conclusion provides an efficient way to realize the invisibility cloaks using artificial metamaterials.
Probing the structural evolution of CuN−, N=9–20, through a comparison of computed electron removal energies and experimental photoelectron spectra
Authors: Yang M. , Yang F. , Jackson K. A. , Jellinek J.
Published: February 2010

Computed electron removal energies for CuN− clusters, N=9–20, are presented for the three lowest-energy isomers obtained from extensive, unbiased searches for the minimum energy structure at each size. The density functional theory (DFT) computations make use of a scheme introduced by Jellinek and Acioli (JA) [J. Chem. Phys. 118, 7783 (2003)] that obtains electron removal energies from DFT orbital energies using corrections based on DFT total energies. The computed removal energies are compared with the measured photoelectron spectra (PES) for CuN−. The patterns of computed removal energies are shown to be isomer specific for clusters in this size range. By matching the computed removal energies to the observed PES, the isomers responsible for the PES are identified. The results of the JA scheme are compared to those obtained using other DFT-based methods.
Ti-decorated C60 as catalyst for hydrogen generation and storage
Authors: Huang Liping , Liu Ying-Chun , Gubbins Keith E. , Nardelli Marco Buongiorno
Published: February 2010

First-principles calculations were carried out to study Ti–C60 nanostructures as catalysts for water dissociation to generate hydrogen and elucidate the influence of water moisture in the air on hydrogen storage capability of such systems. Our results show that both Ti atoms and dimers on C60 can act as reaction centers for water dissociation with much lower energy barriers than that for water splitting in free space (∼5 eV). After water dissociation, Ti atoms are covered with OH groups, their interaction with hydrogen is substantially reduced, and hydrogen adsorption is changed from chemisorption to physisorption. Therefore, care needs to be taken to eliminate moisture if they were designed as efficient hydrogen storage media.
Fluctuation characteristics and transport properties of collisionless trapped electron mode turbulence
Authors: Xiao Yong , Holod Ihor , Zhang Wenlu , Klasky Scott , Lin Zhihong
Published: February 2010

The collisionless trapped electron mode turbulence is investigated by global gyrokinetic particle simulation. The zonal flow dominated by low frequency and short wavelength acts as a very important saturation mechanism. The turbulent eddies are mostly microscopic, but with a significant portion in the mesoscale. The ion heat transport is found to be diffusive and follows the local radial profile of the turbulence intensity. However, the electron heat transport demonstrates some nondiffusive features and only follows the global profile of the turbulence intensity. The nondiffusive features of the electron heat transport is further confirmed by nonlognormal statistics of the flux-surface-averaged electron heat flux. The radial and time correlation functions are calculated to obtain the radial correlation length and autocorrelation time. Characteristic time scale analysis shows that the zonal flow shearing time and eddy turnover time are very close to the effective decorrelation time, which suggests that the trapped electrons move with the fluid eddies. The fluidlike behaviors of the trapped electrons and the persistence of the mesoscale eddies contribute to the transition of the electron turbulent transport from gyro-Bohm scaling to Bohm scaling when the device size decreases.
Note: High-precision microsphere sorting using velocity sedimentation
Authors: Cheng Daniel , Halvorsen Ken , Wong Wesley P.
Published: February 2010

Monodisperse populations of microspheres are desirable for a variety of research and industrial applications, but many desirable sizes and materials can be difficult to synthesize and have limited commercial availability. In this paper, we present an effective, straightforward, and low cost method for sorting polydisperse microspheres into many separate monodisperse samples. The basic approach is to use velocity sedimentation through a density gradient in a long vertical column, followed by carefully targeted extraction. We demonstrate this technique by reducing the coefficient of variation of melamine microspheres from 13% to 1%–4% and glass microspheres from 35% to 3%–8%. This simple and inexpensive method can be used to sort microspheres of many sizes and materials, and is easily scalable, opening the possibility of cheap, monodisperse microspheres.
MoO
3
/poly(9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine) double-interlayer effect on polymer solar cells
Authors: Subbiah Jegadesan , Kim Do Young , Hartel Michael , So Franky
Published: February 2010

A double interlayer composed of MoO3 and poly(9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine) (TFB) was used as an anode contact for bulk heterojunction polymer solar cells. Using this strategy, photovoltaic cells with poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]: [6,6]-phenyl-C61 butyric acid methyl ester (MDMO-PPV:PCBM) blend as a photoactive layer were fabricated. An enhancement in power conversion efficiency of 53% was observed in cells with a double interlayer compared with cells having a PEDOT: PSS interlayer. The enhancement is attributed to the combined effects of electron blocking and enhanced charge extraction from the photoactive layer to the anode.
Quantitative prediction of gas-phase N15 and P31 nuclear magnetic shielding constants
Authors: Prochnow Eric , Auer Alexander A.
Published: February 2010

High-level ab initio benchmark calculations of the N15 and P31 NMR chemical shielding constants for a representative set of molecules are presented. The computations have been carried out at the Hartree–Fock self-consistent field (HF-SCF), density functional theory (DFT) (B-P86 and B3-LYP), second-order Møller–Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), and CCSD augmented by a perturbative treatment of triple excitations [CCSD(T)] level of theory using basis sets of triple zeta quality or better. The influence of the geometry, the treatment of electron correlation, as well as basis set and zero-point vibrational effects on the shielding constants are discussed and the results are compared to gas-phase experimental shifts. As for the first time a study using high-level post-HF methods is carried out for a second-row element, we also propose a family of basis sets suitable for the computation of P31 shielding constants. The mean deviations observed for N15 and P31 are 0.9 [CCSD(T)/13s9p4d3f] and −3.3 ppm [CCSD(T)/15s12p4d3f2g], respectively, when corrected for zero-point vibrational effects. Results obtained at the DFT level of theory are of comparable accuracy to MP2 for N15 and of comparable accuracy to HF-SCF for P31. However, they are not improved by inclusion of zero-point vibrational effects. The PN molecule is an especially interesting case with exceptionally large electron correlation effects on shielding constants beyond MP2 which, therefore, represents an excellent example for further benchmark studies.
The barrier height, unimolecular rate constant, and lifetime for the dissociation of HN2
Authors: Bozkaya Uğur , Turney Justin M. , Yamaguchi Yukio , Schaefer Henry F.
Published: February 2010

Although never spectroscopically identified in the laboratory, hydrogenated nitrogen (HN2) is thought to be an important species in combustion chemistry. The classical barrier height (10.6±0.2 kcal mol−1) and exothermicity (3.6±0.2 kcal mol−1) for the HN2→N2+H reaction are predicted by high level ab initio quantum mechanical methods [up to CCSDT(Q)]. Total energies are extrapolated to the complete basis set limit applying the focal point analysis. Zero-point vibrational energies are computed using fundamental (anharmonic) frequencies obtained from a quartic force field. Relativistic and diagonal Born–Oppenheimer corrections are also taken into account. The quantum mechanical barrier with these corrections is predicted to be 6.4±0.2 kcal mol−1 and the reaction exothermicity to be 8.8±0.2 kcal mol−1. The importance of these parameters for the thermal NOx decomposition (De-NOx) process is discussed. The unimolecular rate constant for dissociation of the HN2 molecule and its lifetime are estimated by canonical transition-state theory and Rice–Ramsperger–Kassel–Marcus theory. The lifetime of the HN2 molecule is here estimated to be 2.8×10−10 s at room temperature. Our result is in marginal agreement with the latest experimental kinetic modeling studies (τ=1.5×10−8 s), albeit consistent with the very rough experimental upper limit (τ<0.5 μs). For the dissociation reaction, kinetic isotope effects are investigated. Our analysis demonstrates that the DN2 molecule has a longer lifetime than the HN2 molecule. Thus, DN2 might be more readily identified experimentally. The ionization potential of the HN2 molecule is determined by analogous high level ab initio methods and focal point analysis. The adiabatic IP of HN2 is predicted to be 8.19±0.05 eV, in only fair agreement with the experimental upper limit of 7.92 eV deduced from sychrothon-radiation-based photoionization mass spectrometry.
Natural advection from a microcantilever heat source
Authors: Kasper Matthew J. , Natrajan Vinay K. , Privorotskaya Natalya L. , Christensen Kenneth T. , King William P.
Published: February 2010

Fluid motion induced by a microcantilever heat source immersed in water is assessed by microscopic particle image velocimetry. Large fluid velocity is observed near the heated cantilever and its magnitude increases with cantilever temperature. Neither Brownian nor thermophoretic motion of the tracer particles can account for these large velocities. Rather, this fluid motion is consistent with buoyancy-driven advection. The observation of natural advection due to a microscopic heat source is important for electronics cooling, performance of thermal sensors, and the thermal processing of small biological samples.
Sequence dependent self-assembly of β-peptides: Insights from a coarse-grained model
Authors: Mondal Jagannath , Sung Bong June , Yethiraj Arun
Published: February 2010

The sequence-directed self-assembly of amphiphilic β-peptides is studied using Monte Carlo simulations. A phenomenological model is employed where each molecule is modeled as a rigid nanorod with side groups located at positions to mimic globally amphiphilic (GA) and nonglobally amphiphilic (non-GA) isomers of β-peptides. The strength and the range of interactions between side groups are chosen based on the types of residues. The simulations show that the aggregation of β-peptides is sensitive to the sequence and the residue types. For one type of β-peptide the GA isomer has a greater tendency to aggregate while for the other the non-GA isomer has a greater tendency to aggregate. The trends observed in the simulations are consistent with recent experiments [Pomerantz et al., J. Am. Chem. Soc. 128, 8730 (2006); Pomerantz et al., Angew. Chem., Int. Ed. 47, 1 (2008)], although the molecules do not spontaneously form the hollow fibers seen in experiment. Simulations with initial configurations as hollow fibers show that the stability of the fibers follows the same trend as the tendency for aggregation. The simulations demonstrate that the details matter: the self-assembly of the molecules is sensitive to the strength of the short-ranged interactions and the size of the side groups, in addition to the global amphiphilicity of the molecules. This suggests the possibility of designing molecules for desired nanostructures.
A comparative ab initio study of neutral and charged kink solitons on conjugated carbon chains
Authors: Mayo M. L. , Gartstein Yu. N.
Published: February 2010

The ground state of odd-N polyynic oligomers CNH2 features kink solitons in carbon-carbon bond-length alternation (BLA) patterns. We perform a systematic first-principles computational study of neutral and singly charged kinks in long oligomers addressing relationships between BLA patterns, electron energy gaps, and accompanying distributions of spin and charge densities, both in vacuum and in the screening solvent environment. A quantitative comparison is made of the results derived with four different ab initio methods: from pure density-functional theory to pure Hartree–Fock (HF) and including two popular hybrid density functionals, B3LYP and BHandHLYP. A clear correlation is demonstrated between the derived spatial extent of kinks and the amount of HF exchange used in the functionals. For charged kinks, we find a substantial difference in the behavior of charge and spin densities.
External potential dynamic studies on the formation of interface in polydisperse polymer blends
Authors: Qi Shuanhu , Zhang Xinghua , Yan Dadong
Published: February 2010

The formation of interface from an initial sharp interface in polydisperse A/B blends is studied using the external potential dynamic method. The present model is a nonlocal coupling model as we take into account the correlation between segments in a single chain. The correlation is approximately expressed by Debye function and the diffusion dynamics are based on the Rouse chain model. The chain length distribution is described by the continuous Schulz distribution. Our numerical calculation indicates that for a wide range of the Flory–Huggins parameter the broadening of interface with respect to time obeys a power law at early time, and the power indices are the same for both monodisperse and polydisperse blends. The power index is larger than that in the local coupling model. However, there is no unified scaling form of the broadening of the interface width if only the interfacial width at equilibrium is taken into account as the characteristic length of the system, because the correlation makes an extra characteristic length in the system, and the polydispersity is related to this length.
Metal-catalyzed crystallization of amorphous carbon to graphene
Authors: Zheng Maxwell , Takei Kuniharu , Hsia Benjamin , Fang Hui , Zhang Xiaobo , Ferralis Nicola , Ko Hyunhyub , Chueh Yu-Lun , Zhang Yuegang , Maboudian Roya , Javey Ali
Published: February 2010

Metal-catalyzed crystallization of amorphous carbon to graphene by thermal annealing is demonstrated. In this “limited source” process scheme, the thickness of the precipitated graphene is directly controlled by the thickness of the initial amorphous carbon layer. This is in contrast to chemical vapor deposition processes, where the carbon source is virtually unlimited and controlling the number of graphene layers depends on the tight control over a number of deposition parameters. Based on the Raman analysis, the quality of graphene is comparable to other synthesis methods found in the literature, such as chemical vapor deposition. The ability to synthesize graphene sheets with tunable thickness over large areas presents an important progress toward their eventual integration for various technological applications.
Dynamics of water at the nanoscale hydrophobic confinement
Authors: Choudhury Niharendu
Published: February 2010

We investigate the effect of solute surface topology created by considering various intermolecular separations of the hydrophobic, paraffinlike plates on the dynamics of water confined between two such plates. The solute plates are made up of 5n-C18H38 molecules arranged in parallel in such a way that all the carbon atoms of the paraffin molecule are lying on the same plane. Results are obtained from extensive molecular dynamics simulations of aqueous solutions of paraffinlike plates in the isothermal-isobaric ensemble. A strong dependence of the translational as well as vibrational dynamics of the confined water molecules on surface topology (intermolecular distance within the paraffinlike plate) has been observed. Analysis of mean squared displacement reveals anomalous nonlinear behavior of the water molecules in the nanoconfined environment.
Effects of side-chain packing on the formation of secondary structures in protein folding
Authors: Yasuda Satoshi , Yoshidome Takashi , Oshima Hiraku , Kodama Ryota , Harano Yuichi , Kinoshita Masahiro
Published: February 2010

We have recently shown that protein folding is driven by the water-entropy gain. When the α-helix or β-sheet is formed, the excluded volumes generated by the backbone and side chains overlap, leading to an increase in the total volume available to the translational displacement of water molecules. Primarily by this effect, the water entropy becomes higher. At the same time, the dehydration penalty (i.e., the break of hydrogen bonds with water molecules) is compensated by the formation of intramolecular hydrogen bonds. Hence, these secondary structures are very advantageous units, which are to be formed as much as possible in protein folding. The packing of side chains, which leads to a large increase in the water entropy, is also crucially important. Here we investigate the roles of the side-chain packing in the second structural preference in protein folding. For some proteins we calculate the hydration entropies of a number of structures including the native structure with or without side chains. A hybrid of the angle-dependent integral equation theory combined with the multipolar water model and the morphometric approach is employed in the calculation. Our major findings are as follows. For the structures without side chains, there is an apparent tendency that the water entropy becomes higher as the α-helix or β-sheet content increases. For the structures with side chains, however, a higher content of α-helices or β-sheets does not necessarily lead to larger entropy of water due to the effect of the side-chain packing. The thorough, overall packing of side chains, which gives little space in the interior, is unique to the native structure. To accomplish such specific packing, the α-helix and β-sheet contents are prudently adjusted in protein folding.
Thermodynamic stability of soft-core Lennard-Jones fluids and their mixtures
Authors: Heyes D. M.
Published: February 2010

Thermodynamic stability of model single component and binary mixture fluids is considered with the Fisher–Ruelle (FR) stability criteria, which apply in the thermodynamic limit, and molecular dynamics (MD) simulation for finite periodic systems. Two soft-core potential forms are considered, ϕ6,1(r)=4[1/(a+r6)2−1/(a+r6)] and ϕ2,3(r)=4[1/(a+r2)6−1/(a+r2)3], where r is the separation between the particle centers. According to FR these are unstable in the thermodynamic limit if a>ac=1/2 and a>ac=(7/32)1/3, respectively. MD simulations with single-component particles show, however, that this transition on typical simulation times is more gradual for finite periodic systems with variation in a on either side of ac. For a<ac, asymmetric density fluctuations are stabilized by the periodic boundary conditions. Also for binary mixtures of (stable) Lennard-Jones and ϕ2,3 particles, phase separation into regions richer in one component than the other was observed for aac, with the unstable component in the mixture breaking up into many long-lived microdroplets which conferred apparent equilibrium thermodynamic behavior (i.e., negligible N-dependence of the average potential energy per particle) in this period.
Thioglycolic acid on the gold (111) surface and Raman vibrational spectra
Authors: Zhou Jian-Ge , Williams Quinton L. , Wu Ruqian
Published: February 2010

The interaction of thioglycolic acid (HSCH2COOH) with the Au(111) surface is investigated, and it is found that at the low coverage the molecule lies down on the substrate. If the mercaptan-hydrogen atom is eliminated, the resulting SCH2COOH molecule is randomly oriented on the surface. If the carboxylic acid group in the HSCH2COOH molecule is deprotonated instead, the HSCH2COO− molecule lies down on the surface. However, when the mercaptan-hydrogen atom in the HSCH2COO− molecule is removed, the resulting SCH2COO− molecule rises up to a certain level on the substrate. The calculated Raman vibrational spectra decipher which compounds and atomic displacements contribute to the corresponding frequencies. We thus propose a consistent mechanism for the deposition of thioglycolic acid on the Au(111) surface.