bluuebunny/crossref_metadata_2025 huggingface dataset:
Colon Interposition Graft for Corrosive Esophageal Stricture: Midterm Functional Outcome
Authors: Ezemba Ndubueze , Eze John C. , Nwafor Ikechukwu A. , Etukokwu Kenneth C. , Orakwe Obinna I.
Published: April 2014

Background

Corrosive esophageal stricture is a major cause of morbidity among Nigerians. In most cases, this follows accidental or parasuicidal ingestion of caustic sodium hydroxide solution (NaOH) often used in the local production of soaps. Various treatment modalities have been advocated for the treatment of esophageal stricture. In this study, we review the results of our adopted technique in the past 10 years for pedicled colonic interposition.

Methods

This is a retrospective study of 21 patients who underwent substernal isoperistaltic pedicled colonic interposition graft for management of corrosive esophageal stricture. The right colon was pulled up into the neck in all the patients without resecting the strictured esophagus.

Results

Long segment strictures and multiple strictures were the main indications for the procedure. The mean duration of the procedure was 339.6 ± 71.1 min. The average intraoperative blood loss was 673.1 ± 398.1 mL. There were two (9.5 %) hospital mortalities. Graft infarction (9.5 %), cervical fistulae (19.0 %), and reflux neo‐esophagitis (14.3 %) were the main non‐fatal complications. In the mid‐term, dysphagia was completely relieved in a little over 84 % (16/19) of patients, while one patient (4.8 %) still experienced reflux neo‐esophagitis requiring treatment. There was no case of gross regurgitation or nocturnal aspiration in the mid‐term.

Conclusions

Although the use of pedicled colonic interposition graft offers a good mid‐term functional outcome with relief of dysphagia, early postoperative morbidity is high. Graft infarction is the single most important factor for poor functional outcome and every effort must be made to prevent its occurrence.
Audit on Preoperative Fasting of Elective Surgical Patients in an African Academic Medical Center
Authors: Gebremedhn Endale Gebreegziabher , Nagaratnam Vidhya Bates
Published: April 2014

Background

Preoperative fasting is a requisite before anesthesia. The main reason for preoperative fasting is to reduce gastric volume and acidity and thus decrease the risk of pulmonary aspiration. However, preoperative fasting is usually prolonged beyond the recommended time for various reasons. Despite the many adverse effects of prolonged fasting, patients sometimes fasted for a prolonged time when surgery was delayed for different reasons at the University of Gondar Hospital. The aim of this study was to assess the duration of preoperative fasting for elective surgery.

Methods

A cross‐sectional study was conducted from March 10 to April 10, 2013. Patients were interviewed 24 h after surgery. All 43 patients who were under anesthesia while operated on during the study period were included.

Result

Of the 43 patients included in the study, 35 were adults and 8 were children. The minimum, maximum, and mean fasting hours for food were 5, 96, and 19.60, respectively, and more than 50 % of the patients fasted from food twice as long as recommended. The minimum, maximum, and mean fasting hours for fluid were 5, 19, and 12.72, respectively. More than 95 % of the patients fasted from fluid longer than recommended.

Conclusion

Most patients fasted from both food (92 %) and fluid (95 %) longer than the fasting time recommended by the AAGBI, ASA, RCOA, and RCN fasting guidelines. Anesthetists, surgeons, and nurses need to revise operation lists every day in the operating theatres and resuscitate the patients when surgery is delayed for various reasons. A preoperative fasting guideline should be developed and implemented in the University of Gondar Hospital.
The Relative Proportions of Different Lipid Classes and their Fatty Acid Compositions Change with Culture Age in the Cariogenic Dental Pathogen Streptococcus mutans UA159
Authors: Custer Jenny E. , Goddard Bryan D. , Matter Stephen F. , Kaneshiro Edna S.
Published: April 2014

The oral cariogenic bacterial pathogen Streptococcus mutans strain UA159 has become an important research organism strain since its genome was sequenced. However, there is a paucity of information on its lipidome using direct analytical biochemical approaches. We here report on comprehensive analyses of the major lipid classes and their fatty acids in cells grown in batch standing cultures. Using 2‐D high‐performance thin‐layer chromatography lipid class composition changes were detected with culture age. More lipid components were detected in the stationary‐phase compared to log‐phase cells. The major lipids identified included 1,3‐bis(sn‐3′‐phosphatidyl)‐sn‐glycerol (phosphatidylglycerol), 1,3‐diphosphatidylglycerol (cardiolipin), aminoacyl‐phosphatidylglycerol, monoglucosyldiacylglycerol, diglucosyldiacylglycerol, diglucosylmonoacylglycerol and, glycerophosphoryldiglucosyldiacylglycerol. Culture age also affected the fatty acid composition of the total polar lipid fraction. Thus, the major lipid classes detected in log‐phase and stationary‐phase cells were isolated and their fatty acids were analyzed by gas–liquid chromatography to determine the basis for the fatty acid compositional changes in the total polar lipid fraction. The analyses showed that the relative proportions of these acids changed with culture age within individual lipid classes. Hence fatty acid changes in the total polar lipid fraction reflected changes in both lipid class composition and fatty acid compositions within individual lipid classes.
Rumen Metabolism of 22:6n‐3 In Vitro is Dependent on its Concentration and Inoculum Size, but Less Dependent on Substrate Carbohydrate Composition
Authors: Vlaeminck B. , Braeckman T. , Fievez V.
Published: April 2014

Ruminal disappearance of linoleic and linolenic acid has been studied extensively. Less is known of the metabolism of docosahexaenoic acid (22:6n‐3). The aim of this study was to identify factors which affect the disappearance of 22:6n‐3 during in vitro batch incubations using rumen fluid from sheep. In experiment 1, the effect of the rumen fluid/buffer ratio (0.2 or 0.4), substrate (cellulose or cellulose/glucose), time of 22:6n‐3 addition (0.08 mg/mL after 0 or 6 h of incubation) and incubation time (24 or 48 h) was evaluated. A mixture design was used in experiment 2 to evaluate the effect of carbohydrate type (cellulose, glucose, cellobiose and starch) on 22:6n‐3 disappearance (0.08 mg/mL). In experiment 3, several concentrations of 22:6n‐3 (0.05–0.30 mg/mL) were evaluated with different substrate mixtures (combinations of cellobiose, starch and cellulose). In a final experiment, the effect of the rumen fluid/buffer ratio (0.20, 0.35 and 0.50) and substrate (glucose, cellobiose and starch) was evaluated. In this experiment, 22:6n‐3 was added as a proportion of rumen fluid ranging from 0.1 to 0.4 mg/mL rumen fluid, contrary to former experiments where concentrations were relative to culture medium. Low levels of 22:6n‐3 (0.05 mg/mL) allowed extensive metabolism whereas increasing amounts of 22:6n‐3 hampered its disappearance. A greater proportion of rumen fluid resulted in increased disappearance of 22:6n‐3. The effect of carbohydrate type was small compared with the former two factors. These results suggest that in vitro metabolism of 22:6n‐3 is mostly dictated by the conditions at the start of the incubation, i.e., inoculum, probably reflecting the density of bacteria able to metabolize 22:6n‐3.
Safety and usefulness of the Sweet Tip™ type screw‐in lead for pacemakers
Authors: Nakazato Yuji
Published: April 2014

In the current cardiac device implantation practice, screw‐in leads are important for stability of atrial and ventricular pacing. There are two screw‐in leads, the Sweet Tip™ and the retractable screw‐in lead; both are widely used. The difference between them is the exposure of the helix during placement. The Sweet Tip lead has an exposed screw covered with mannitol to prevent undesirable entrapment or perforations before fixation. The mannitol melts within several minutes, after which direct fixation is feasible. The Sweet Tip™ has a simple mechanical structure, which facilitates fixation. This review emphasizes the usefulness of the Sweet Tip™ screw‐in lead and suggests how to apply it safely.
The cutoff level of free/total prostate specific antigen (f/t PSA) ratios in the diagnosis of prostate cancer: A validation study on a Turkish patient population in different age categories
Authors: Erol Bulent , Gulpinar Murat Tolga , Bozdogan Gurdal , Ozkanli Seyma , Onem Kadir , Mungan Görkem , Bektas Sibel , Tokgoz Husnu , Akduman Bulent , Mungan Aydin
Published: April 2014

We investigated an optimal cutoff level of free/total PSA ratios (f/t PSA) in predicting prostate cancer in different age groups, focusing on the avoidance of unnecessary prostate biopsies. A total of 4955 men were enrolled into the study. Serum tPSA, fPSA, and f/t PSA ratios were determined for the study population. All males who had suspicious digital rectal examination and tPSA > 4 ng/mL underwent transrectal ultrasonography‐guided prostate biopsy. Receiver operating characteristic (ROC) curves for each group were generated by plotting the sensitivity versus 1‐specificity for the f/t PSA ratio. The sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were obtained using various f/t PSA ratio cutoffs for different age groups. There were 657 patients with a PSA level of 4–10 ng/mL. According to sensitivity and specificity f/t% PSA cutoff points were determined to be 10%, 15%, 15%, and 10% in 50–59 years, 60–69 years, >70 years, and all ages categories, respectively, in patients with initial PSA level of 4–10 ng/mL. f/t PSA ratio had an area under the curve (AUC) value of 0.81 (95% confidence level: 0.80–0.82) for all age groups in detecting prostate cancer. f/t PSA ratio has an AUC value of 0.669 (0.632–0.705) in detecting prostate cancer among patients with a PSA level of 4–10 ng/mL. Ten percent of f/t PSA ratio had the highest specificity with PLR and 30% f/t PSA ratio had the highest sensitivity with lower NLR in the all‐age categories. The current study shows that the use of f/t PSA ratio in patients with PSA levels of 4–10 ng/mL should enhance the specificity of PSA screening and decrease the number of unnecessary biopsies. The age‐related changes warrant further investigation in a large, multicentric, and multinational population to improve the clinical use of f/t PSA cutoffs.
Trainee Involvement in Transforaminal Epidural Steroid Injections Associated With Increased Incidence of Vasovagal Reactions
Authors: Schneider Byron , Kennedy David J. , Casey Ellen , Smuck Matthew , Conrad Bryan , Plastaras Christopher
Published: April 2014

Objectives

To evaluate whether trainee involvement (resident and fellow) during transforaminal epidural steroid injections (TFESI) results in greater rates of vasovagal reactions.

Design

Retrospective study on consecutive patients.

Setting

Single academic medical center with multiple attending physicians and trainees.

Participants

A total of 2642 consecutive subjects undergoing 4482 TFESI were analyzed from March 8, 2004, to January 30, 2009.

Main Outcome Measures

The Pearson χ2 test was used to determine the relationship between vasovagal reactions and level of trainee involvement.

Results

A total of 4482 TFESIs were performed, with 157 (3.5%) of procedures complicated by a vasovagal reaction. An attending physician performed 2884 (64.3%) procedures without trainee involvement, with only 79 (2.7%) vasovagal reaction noted. A fellow was involved in 723 (16.1%) procedures, with 30 (4.1%) noted to have a vasovagal reaction. A resident was involved in 875 (19.5%) procedures, with 48 (5.5%) having a vasovagal reaction. Overall, trainees were involved in 1598 (35.7%) cases, of which 78 (4.9%) were complicated by vasovagal reaction. When a trainee was involved in the case, there was a greater incidence of vasovagal episodes (P < .001, χ2 = 16.047). Although there was a trend towards greater vasovagal rates with residents over fellows, this did not reach statistical difference.

Conclusions

Vasovagal reactions can occur with spine injection procedures and may result in premature procedure termination or other adverse events. Although this retrospective study has significant potential for bias, it appears that trainee involvement in a TFESI is associated with a greater incidence of vasovagal reaction (P < .001, χ2 = 16.047).
On the importance of image formation optics in the design of infrared spectroscopic imaging systems
Authors: Mayerich David , van Dijk Thomas , Walsh Michael J. , Schulmerich Matthew V. , Carney P. Scott , Bhargava Rohit
Published: April 2014

Theory explains the influence of optical configuration on recorded data in infrared spectroscopic imaging.
Size-tunable synthesis and luminescent properties of Gd(OH)3:Eu3+and Gd2O3:Eu3+hexagonal nano-/microprisms
Authors: Li Guogang , Liang Yujun , Zhang Mengfei , Yu Dongyan
Published: April 2014

Size-tunable Gd(OH)3:Eu3+and Gd2O3:Eu3+hexagonal nano-/microprisms were synthesized by a facile and large scale homogenous precipitation method, and their photoluminescent and cathodoluminescent properties were investigated.
DNA and aptamer stabilized gold nanoparticles for targeted delivery of anticancer therapeutics
Authors: Latorre Alfonso , Posch Christian , Garcimartín Yolanda , Celli Anna , Sanlorenzo Martina , Vujic Igor , Ma Jeffrey , Zekhtser Mitchell , Rappersberger Klemens , Ortiz-Urda Susana , Somoza Álvaro
Published: April 2014

Aptamer modified gold nanoparticles target malignant cells. Anti-cancer therapeutics are released after cleavage of a self-immolative linker by intracellular triggers.
Porous Ni–Mn oxide nanosheets in situ formed on nickel foam as 3D hierarchical monolith de-NOx catalysts
Authors: Cai Sixiang , Zhang Dengsong , Shi Liyi , Xu Jing , Zhang Lei , Huang Lei , Li Hongrui , Zhang Jianping
Published: April 2014

The nickel foam decorated with porous Ni–Mn oxide nanosheets as 3D hierarchical monolith catalysts shows excellent de-NOx performance.
Macroporous antibacterial hydrogels with tunable pore structures fabricated by using Pickering high internal phase emulsions as templates
Authors: Zou Shengwen , Wei Zengjiang , Hu Yang , Deng Yonghong , Tong Zhen , Wang Chaoyang
Published: April 2014

Pickering-based antibacterial hydrogels with tunable pore structures were fabricated by using high internal phase emulsion templates.
Aqueous solubilization of hydrophobic supramolecular metal–organic nanocapsules
Authors: Kumari H. , Kline S. R. , Atwood J. L.
Published: April 2014

Micelles of surfactant solubilized metal-seamed pyrogallol[4]arene based organic nanocapsules are synthesized and characterized using in situ neutron scattering and dynamic light scattering techniques, which show trends in sizes as a function of alkyl tails of pyrogallols and surfactants.
Enantiomeric differentiation of aromatic amino acids using traveling wave ion mobility-mass spectrometry
Authors: Domalain Virginie , Hubert-Roux Marie , Tognetti Vincent , Joubert Laurent , Lange Catherine M. , Rouden Jacques , Afonso Carlos
Published: April 2014

The present work describes the first differentiation of amino acids enantiomers using the coupling of traveling wave ion mobility and mass spectrometry.
The alloying element dependence of the local lattice deformation and the elastic properties of Ni3Al: A molecular dynamics simulation
Authors: Yang Xiyuan , Hu Wangyu
Published: April 2014

Molecular dynamics (MD) together with the modified analytical embedded atom method (MAEAM) is employed to study the alloying elements (Re, Ru, Co, and Ta) dependence of the elastic properties of L12-Ni3Al. The investigations indicate that the calculated elastic properties of Ni3Al are in reasonable agreement with the previous results. The substituting formation energies of the alloying elements in Ni3Al are calculated to determine the site preference. It is found out that Re, Ru, and Ta atoms prefer to occupy the Al sites, and the Co atom prefers to occupy the Ni site. Based on Re, Ru, and Ta substituting the 1st, 2nd, 3rd, and 4th nearest-neighbor atoms, we ascertain that the substituting manners of these alloying elements have a decisive effect on the bulk modulus and the local crystal lattice of Ni3Al. Moreover, for Re, the bonding interaction plays a predominant role in the improvement in the bulk modulus of Ni3Al, whereas the size effect of Ru and Ta on the improvement in the bulk modulus is more obvious. Finally, the potential reasons of which the alloying elements enhance the bulk modulus are discussed in details.
Simulation study of the effects of surface chemistry and temperature on the conformations of ssDNA oligomers near hydrophilic and hydrophobic surfaces
Authors: Elder Robert M. , Jayaraman Arthi
Published: April 2014

We study the effects of the presence of a hydrophilic and a hydrophobic surface on the conformations and interactions of a single-stranded DNA (ssDNA) oligomer using atomistic molecular dynamics, umbrella sampling, and temperature-replica exchange. Our simulations capture the expected interactions between the ssDNA and the two surfaces (e.g., hydrogen bonds, hydrophobic interactions), but we find that the surface chemistry does not strongly affect the exposure of the relatively hydrophobic nucleobases or the hydrophilic phosphate backbone in a 16-base ssDNA. Likewise, the surfaces do not strongly affect the preferred size of the ssDNA compared to bulk solution, although the hydrophilic surface does favor slightly more compact ssDNA conformations than the hydrophobic surface. In more compact conformations, the negative charge of the ssDNA is more concentrated, and the energetic interactions of the DNA and DNA-bound counterions with the hydrophilic surface are more favorable, which consequently favors smaller ssDNA sizes. Increasing temperature, regardless of the presence or chemistry of a surface, makes it less unfavorable for the ssDNA to assume both compact and extended conformations. With increasing temperature the free energy cost of assuming a compact conformation is reduced to a greater extent than the cost of assuming an extended conformation. The reason for this difference is the entropically favorable release of DNA-bound water molecules upon assuming a compact conformation. Increasing temperature decreases water-DNA interactions while surprisingly increasing counterion-DNA interactions, changes which are attributed to the relative balance of entropic and energetic contributions for water molecules and counterions bound to the ssDNA.
Magnetic degradation of thin film multilayers during ion milling
Authors: Read J. C. , Braganca P. M. , Robertson N. , Childress J. R.
Published: April 2014

We present a study of Ar ion milling-induced damage in exchange biased IrMn/CoFe/Ag-based magnetic multilayer thin films. While process variations determine the change in CoFe magnetic properties, the distance from the ion milling front to the IrMn/CoFe interface dominates the extent of exchange bias damage. Remarkably, the interfacial coupling energy Jk can be reduced by 50% before any removal of the CoFe pinned layer. We attribute the losses to microstructural changes and damage effects where cap material is driven into the CoFe layer below. Disturbance depth estimates from ion impact simulations agree reasonably with the observed length scales of damage.
Anisotropic orbital occupation and Jahn-Teller distortion of orthorhombic YMnO3 epitaxial films: A combined experimental and theoretical study on polarization-dependent x-ray absorption spectroscopy
Authors: Haw Shu-Chih , Lee Jenn-Min , Chen Shin-Ann , Lu Kueih-Tzu , Lin Pao-An , Lee Chih-Hao , Lee Ming-Tao , Pi Tun-Wen , Hu Zhiwei , Chen Jin-Ming
Published: April 2014

The b-axis oriented orthorhombic YMnO3 (o-YMnO3) epitaxial films on a YAlO3 (010) substrate were fabricated with pulsed-laser deposition. The anisotropic orbital occupation and Jahn-Teller (JT) distortion of an o-YMnO3 film were investigated with polarization-dependent x-ray absorption spectra and configuration-interaction multiplet-cluster calculations. A significant energy difference, ∼3.8 eV, for the main white line along E//b and E//a in polarization-dependent Mn K-edge spectra of o-YMnO3 indicates an extraordinary JT distortion and significant anisotropic Mn–O bonding within the ab plane in the o-YMnO3 film. Most importantly, although the orbital occupation of 3d electrons in o-YMnO3 films is almost the same as that in single crystalline o-DyMnO3, the JT distortion of o-YMnO3 films is larger than that of single crystalline o-DyMnO3, deduced from the multiplet calculations. We speculate that this JT distortion predominantly contributes to the origin of the cycloidal spin deformation in bulk o-YMnO3, because of a suppressed nearest-neighbor superexchange interaction and an enhanced next-nearest-neighbor superexchange interaction. These complementary results provide insight into the origin of the E-type magnetic configuration of o-YMnO3.
Exploration of zeroth-order wavefunctions and energies as a first step toward intramolecular symmetry-adapted perturbation theory
Authors: Gonthier Jérôme F. , Corminboeuf Clémence
Published: April 2014

Non-covalent interactions occur between and within all molecules and have a profound impact on structural and electronic phenomena in chemistry, biology, and material science. Understanding the nature of inter- and intramolecular interactions is essential not only for establishing the relation between structure and properties, but also for facilitating the rational design of molecules with targeted properties. These objectives have motivated the development of theoretical schemes decomposing intermolecular interactions into physically meaningful terms. Among the various existing energy decomposition schemes, Symmetry-Adapted Perturbation Theory (SAPT) is one of the most successful as it naturally decomposes the interaction energy into physical and intuitive terms. Unfortunately, analogous approaches for intramolecular energies are theoretically highly challenging and virtually nonexistent. Here, we introduce a zeroth-order wavefunction and energy, which represent the first step toward the development of an intramolecular variant of the SAPT formalism. The proposed energy expression is based on the Chemical Hamiltonian Approach (CHA), which relies upon an asymmetric interpretation of the electronic integrals. The orbitals are optimized with a non-hermitian Fock matrix based on two variants: one using orbitals strictly localized on individual fragments and the other using canonical (delocalized) orbitals. The zeroth-order wavefunction and energy expression are validated on a series of prototypical systems. The computed intramolecular interaction energies demonstrate that our approach combining the CHA with strictly localized orbitals achieves reasonable interaction energies and basis set dependence in addition to producing intuitive energy trends. Our zeroth-order wavefunction is the primary step fundamental to the derivation of any perturbation theory correction, which has the potential to truly transform our understanding and quantification of non-bonded intramolecular interactions.
Structural and elastic properties of a hypothetical high density sp2-rich amorphous carbon phase
Authors: Wang L. L. , Zhao M.
Published: April 2014

We report a hypothetical sp2-rich high-density amorphous carbon (sp2-HDAC) phase that is achieved from glassy carbon at high pressure and temperature (151 GPa and nearly 4100 K) based on molecular dynamics calculations. The systemically theoretical investigation demonstrates that the sp2-HDAC phase exhibits a high incompressibility with a bulk modulus of B = 478 GPa and elastic constants of c11 = 932, c22 = 730, and c33 = 921 GPa, which are comparable with these of diamond. Moreover, the high shear modulus of G = 301 GPa enlists this sp2-HDAC phase to exhibit good shear resistance in comparison with other sp2-bonded carbon phases such as graphene and crystalline H-6 carbon phase.
Rationalizing the role of structural motif and underlying electronic structure in the finite temperature behavior of atomic clusters
Authors: Susan Anju , Joshi Kavita
Published: April 2014

Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al36 which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature.
Curvature and geometric modules of noncommutative spheres and tori
Authors: Arnlind Joakim
Published: April 2014

When considered as submanifolds of Euclidean space, the Riemannian geometry of the round sphere and the Clifford torus may be formulated in terms of Poisson algebraic expressions involving the embedding coordinates, and a central object is the projection operator, projecting tangent vectors in the ambient space onto the tangent space of the submanifold. In this note, we point out that there exist noncommutative analogues of these projection operators, which implies a very natural definition of noncommutative tangent spaces as particular projective modules. These modules carry an induced connection from Euclidean space, and we compute its scalar curvature.
Quantum conductance of zigzag graphene oxide nanoribbons
Authors: Kan Zhe , Nelson Christopher , Khatun Mahfuza
Published: April 2014

The electronic properties of zigzag graphene oxide nanoribbons (ZGOR) are presented. The results show interesting behaviors which are considerably different from the properties of the perfect graphene nanoribbons (GNRs). The theoretical methods include a Huckel-tight binding approach, a Green's function methodology, and the Landauer formalism. The presence of oxygen on the edge results in band bending, a noticeable change in density of states and thus the conductance. Consequently, the occupation in the valence bands increase for the next neighboring carbon atom in the unit cell. Conductance drops in both the conduction and valence band regions are due to the reduction of allowed k modes resulting from band bending. The asymmetry of the energy band structure of the ZGOR is due to the energy differences of the atoms. The inclusion of a foreign atom's orbital energies changes the dispersion relation of the eigenvalues in energy space. These novel characteristics are important and valuable in the study of quantum transport of GNRs.
A center frequency adjustable narrow band filter for the detection of weak single frequency signal
Authors: Xin Yunhong , Xiang ZhenMing , Dong LeMing , Zhu Bing , Cao Hui , Fang Yu
Published: April 2014

We describe and implement a center frequency adjustable narrow band filter based on the crystal filter for the detection of weak single frequency signal. It is formed by a multiplier, a direct digital frequency synthesizer, a multi-stage crystal bandpass filter, and a micro control unit which is used to set the center frequency of the filter. A theoretical study is proposed and experimentally validated. The test results show that the 3 db and 20 db bandwidths are 0.84 Hz and 2.73 Hz, respectively, and the filter system can effectively detect the signal with amplitude below 1 μV and a frequency which ranges from 10 Hz to the frequency that is mainly limited by the components applied.
Anomalous properties of water predicted by the BK3 model
Authors: Kiss Péter T. , Baranyai András
Published: April 2014

Recently, we proposed a new model for water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. We presented a detailed description of the development of this classical, polarizable model, and a large number of calculated properties. The model provided excellent estimates for ambient liquid properties and reasonably good results from high-pressure solids to gas-phase clusters. In this paper we present results of extensive calculations for temperature-dependent water anomalies in terms of the pressure. The calculated isobars of the temperature-density and the self-diffusion diagrams provide excellent estimates of the experimental values. The estimated compressibility isobars perfectly match the experimental ones if we shift our numbers by ∼10 K upwards. The calculated pressure-dependent viscosity values are excellent at higher temperatures and qualitatively correct at lower temperatures.
Structural effects of field emission from GaN nanofilms on SiC substrates
Authors: Chen Cheng-Cheng , Wang Ru-Zhi , Liu Peng , Zhu Man-Kang , Wang Bi-Ben , Yan Hui
Published: April 2014

GaN nanofilms (NFs) with different structures are grown on SiC substrates by pulsed laser deposition under different conditions. The synthesized GaN NFs are studied by X-ray diffraction, field-emission (FE) scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GaN NFs are composed of diversified GaN nanoparticles with a diameter of 9–38 nm, thickness of 10–50 nm, and roughness of 0.22–13.03 nm. FE from the GaN NFs is structure dependent, which is explained by stress changing the band gap of the NFs. By structure modulation, the turn-on field of GaN NFs can be as low as 0.66 V/μm at a current density of 1 μA/cm2, with a current density of up to 1.1 mA/cm2 at a field of 4.18 V/μm. Fowler-Nordheim curves of some samples contain multiple straight lines, which originate from the structural change and diversification of GaN nanoparticles under an applied field. Overall, our results suggest that GaN NFs with excellent FE properties can be prepared on SiC substrates, which provides a new route to fabricate high-efficiency FE nanodevices.
Enhanced spin figure of merit in an Aharonov-Bohm ring with a double quantum dot
Authors: Zhou Xingfei , Qi Fenghua , Jin Guojun
Published: April 2014

We theoretically investigate the thermoelectric effects in an Aharonov-Bohm ring with a serially coupled double quantum dot embedded in one arm. An external magnetic field is perpendicularly applied to the two dots. Using the nonequilibrium Green's function method in the linear-response regime, we calculate the charge and spin figures of merit. When the energy levels of the two quantum dots are equal and the system is connected to two normal leads, a large spin figure of merit (ZsT ≈ 4.5) accompanying with a small charge figure of merit (ZcT ≈ 0) can be generated due to the remarkable bipolar effect. Further, when the system is connected to two ferromagnetic leads, the spin figure of merit can reach even a higher value about 9. Afterwards, we find that ZsT is enhanced while ZcT is reduced in the coaction of the Aharonov-Bohm flux and Rashba spin-orbit coupling. It is argued that the bipolar effect is positive (negative) to spin (charge) figure of merit in the presence of level detuning of the two quantum dots and intradot Coulomb interactions, respectively. Also, we propose a possible experiment to verify our results.
Hydride vapor phase epitaxy and characterization of high-quality ScN epilayers
Authors: Oshima Yuichi , Víllora Encarnación G. , Shimamura Kiyoshi
Published: April 2014

The heteroepitaxial growth of ScN films was investigated on various substrates by hydride vapor phase epitaxy (HVPE). Single crystalline mirror-like ScN(100) and ScN(110) layers were successfully deposited on r- and m-plane sapphire substrates, respectively. Homogeneous stoichiometric films (N/Sc ratio 1.01 ± 0.10) up to 40 μm in thickness were deposited. Their mosaicity drastically improved with increasing the film thickness. The band gap was determined by optical methods to be 2.06 eV. Impurity concentrations including H, C, O, Si, and Cl were investigated through energy dispersive X-ray spectrometry and secondary ion mass spectrometry. As a result, it was found that the presence of impurities was efficiently suppressed in comparison with that of HVPE-grown ScN films reported in the past, which was possible thanks to the home-designed corrosion-free HVPE reactor. Room-temperature Hall measurements indicated that the residual free electron concentrations ranged between 1018–1020 cm−3, which was markedly lower than the reported values. The carrier mobility increased monotonically with the decreasing in carrier concentration, achieving the largest value ever reported, 284 cm2 V−1 s−1 at n = 3.7 × 1018 cm−3.
A morphological and structural approach to evaluate the electromagnetic performances of composites based on random networks of carbon nanotubes
Authors: De Vivo B. , Lamberti P. , Spinelli G. , Tucci V.
Published: April 2014

Small quantities of carbon nanotubes (CNTs) in polymer resins allow to obtain new lightweight nanocomposites suitable for microwave applications, such as efficient electromagnetic shielding or radar absorbing materials. The availability of appropriate simulation models taking into account the morphological and physical features of such very interesting composites is very important for design and performance optimization of devices and systems. In this study, a 3-dimensional (3D) numerical structure modeling the morphology of a CNT-based composite is considered in order to carry out a computational analysis of their electromagnetic performances. The main innovative features of the proposed model consists in the identification of a resistance and capacitance network whose values depend on the filler geometry and loading and whose complexity is associated with the percolation paths. Tunneling effect and capacitive interactions between the individual conductive particles are properly taken into account. The obtained network allows an easy calculation in a wide frequency range of the complex permittivity and others electromagnetic parameters. Moreover, a reliable sensitivity analysis concerning the impact of some crucial parameters, such as the CNTs properties and the dielectric permittivity of the neat resin, on the electromagnetic features of the resulting composites can be carried out. The model predictions are in good agreement with existing experimental data, suggesting that the proposed model can be a useful tool for their design and performance optimization in the microwave range.
Circular dichroism of graphene-based absorber in static magnetic field
Authors: Wang Min , Wang Yanqin , Pu Mingbo , Hu Chenggang , Wu Xiaoyu , Zhao Zeyu , Luo Xiangang
Published: April 2014

Recently, the graphene-based absorber captures much attention due to its bright potential. In this paper, a modeling study of graphene-based absorber is made for variable magnetostatic bias, i.e., the magnetic circular dichroism (MCD). A strong MCD signal about ΔA = 0.94 is obtained in 7 T for a uniform graphene-based absorber. By periodically patterning subwavelength holes on the graphene, the structured absorber exhibits two obvious peaks induced by cavity resonance and localized resonance of meta-surface in 0 T, respectively. As the magnetic field increases, the absorption peaks show quite different electromagnetic response for the two kinds of circularly polarized lights. Two distinct MCDs signals of 0.711 at 2.02 THz and 0.91 at 2.49 THz in 7 T are observed. The results are well explained by a modified equivalent circuit model.
Inelastic tunneling conductance and magnetoresistance investigations in dual ion-beam sputtered CoFeB(110)/MgO/CoFeB (110) magnetic tunnel junctions
Authors: Bhusan Singh Braj , Chaudhary Sujeet
Published: April 2014

Magnetic tunnel junctions (MTJs) comprising Ta(5)/NiFe(5)/IrMn(15)/CoFeB(5)/Mg(1)/MgO(3.5)/ CoFeB(5)/Ta(5)/Ag(20) (thickness in nm) with (110) oriented CoFeB layers are grown using dual ion beam sputtering. The tunnel magnetoresistance (TMR) of MTJs is found to be significantly bias dependent and exhibits zero bias anomaly (ZBA) which is attributed to the presence of magnetic impurities or diffusion of Mn from antiferromagnetic IrMn in the barrier. Adjacent to the ZBA, two peaks at 24 ± 3 mV and 34 ± 3 mV are also observed, which differ both in intensity as well as their position in the antiparallel and parallel magnetic states, suggesting that they are due to magnon excitations. In addition to this, a phonon peak at 65 ± 3 mV is also observed. The effect of temperature on the inelastic and elastic tunneling contributions is studied in detail in 25–300 K range using the Glazman and Matveev model. Ten series of localized states are found to be involved in hopping conduction in the forbidden gap of MgO barrier. The effect of presence of such inelastic channels is found to be insignificant at low temperatures yielding sizeable enhancement in TMR.
Oxygen transport in the internal xenon plasma of a dispenser hollow cathode
Authors: Capece Angela M. , Polk James E. , Mikellides Ioannis G. , Shepherd Joseph E.
Published: April 2014

Reactive gases such as oxygen and water vapor modify the surface morphology of BaO dispenser cathodes and degrade the electron emission properties. For vacuum cathodes operating at fixed temperature, the emission current drops rapidly when oxygen adsorbs on top of the low work function surface. Previous experiments have shown that plasma cathodes are more resistant to oxygen poisoning and can operate with O2 partial pressures one to two orders of magnitude higher than vacuum cathodes before the onset of poisoning occurs. Plasma cathodes used for electric thrusters are typically operated with xenon; however, gas phase barium, oxygen, and tungsten species may be found in small concentrations. The densities of these minor species are small compared with the plasma density, and thus, their presence in the discharge does not significantly alter the xenon plasma parameters. It is important, however, to consider the transport of these minor species as they may deposit on the emitter surface and affect the electron emission properties. In this work, we present the results of a material transport model used to predict oxygen fluxes to the cathode surface by solving the species conservation equations in a cathode with a 2.25 mm diameter orifice operated at a discharge current of 15 A, a Xe flow rate of 3.7 sccm, and 100 ppm of O2. The dominant ionization process for O2 is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O2 are not. The model shows that the oxygen flux to the surface is not diffusion-limited; therefore, the high resistance to oxygen poisoning observed in plasma cathodes likely results from surface processes not considered here.
Recent advances in the use of metal oxide-based photocathodes for solar fuel production
Authors: Awad Nasser K. , Ashour Elsayed A. , Allam Nageh K.
Published: April 2014

Harvesting solar energy for the production of clean fuel by a photoelectrochemical system is a very attractive, yet a challenging task. This review focuses on the recent efforts done to tailor metal oxide-based photocathode materials for the solar-driven hydrogen production. The materials are classified into three categories: simple oxides, complex oxides, and photocathodes used in p-n self-biased heterojunction cells. Generally, three strategies have been recommended to tailor p-type metal oxide semiconductors to meet the requirements for efficient solar-driven water splitting, namely (1) coating the p-type metal oxide either with a protective layer or a dye, (2) using co-catalyst, and (3) merging the p-type material with an n-type photoanode with the proper optical and electrical properties. In the light of those strategies, the optical, structural, and photoelectrochemical characteristics of such assemblies are discussed.
Growth mechanism of graphene on platinum: Surface catalysis and carbon segregation
Authors: Sun Jie , Nam Youngwoo , Lindvall Niclas , Cole Matthew T. , Teo Kenneth B. K. , Woo Park Yung , Yurgens August
Published: April 2014

A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently “grow from below.” By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000 °C growth temperature.
Grain size effect on the giant dielectric constant of CaCu3Ti4O12 nanoceramics prepared by mechanosynthesis and spark plasma sintering
Authors: Ahmad Mohamad M. , Yamada Koji
Published: April 2014

In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.
Tuning thermal conductance in the twisted graphene and gamma graphyne nanoribbons
Authors: Wei Xiaolin , Guo Gencai , Ouyang Tao , Xiao Huaping
Published: April 2014

Taking graphene nanoribbons (GNRs) and gamma-graphyne nanoribbons (GYNRs) as examples, we demonstrate that the twisted deformation is an efficient method to modulate the thermal transport properties of materials. The nonequilibrium Green's function results show that the thermal conductance of this two carbon nanoribbons can be modulated controllably and reversibly over a wide range (more than 55% at room temperature) by controlling the twisted angle, while the tuning range of the twisted angle depends on the width and length of the system. The further analysis reveals that the reduction of thermal conductance mainly originates from the phonon scattering due to the inhomogeneous force constant in the twisted nanoribbons. These interesting findings indicate that twisted GNRs and GYNRs can be utilized as thermal conductance modulators and provide useful guidance for designing materials with desired thermal conductance.
Microscopic analysis of non-equilibrium dynamics in the semiconductor-laser gain medium
Authors: Hader J. , Moloney J. V. , Koch S. W.
Published: April 2014

Fully microscopic many-body calculations are used to analyze the carrier dynamics in situations where a strong sub-picosecond pulse interacts with an inverted semiconductor quantum well. Electron-electron and electron-phonon scatterings are calculated on a second Born-Markov level. Intra-subband scatterings on a scale of tens of femtoseconds are shown to quickly re-fill the kinetic holes created in the carrier distributions during the pulse amplification. Even for sub-100 fs pulses, this significantly influences the pulse amplification as well as its spectral dependence. Interband scatterings on a few picosecond timescale limit the possibly achievable repetition rate in pulsed semiconductor lasers.
Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures
Authors: Douglas Peter M. J. , Affek Hagit P. , Ivany Linda C. , Houben Alexander J. P. , Sijp Willem P. , Sluijs Appy , Schouten Stefan , Pagani Mark
Published: April 2014

Significance

Reconstructions of ancient high-latitude climates can help to constrain the amplification of global warming in polar environments. Climate models cannot reproduce the elevated high-latitude temperature estimates in the Eocene epoch, possibly indicating problems in simulating polar climate change. Widely divergent near-Antarctic Eocene sea surface temperature (SST) estimates, however, question the evidence for extreme warmth. Our analysis of multiple temperature proxies near the Antarctic Peninsula improves intersite comparisons and indicates a substantial zonal SST gradient between the southwest Pacific and South Atlantic. Simulations of Eocene ocean temperatures imply that the formation of deep water in the southwest Pacific partly accounts for this SST gradient, suggesting that climate models underestimate Eocene SSTs in regions where the thermohaline circulation leads to relatively high temperatures.
The evolution of self-control
Authors: MacLean Evan L. , Hare Brian , Nunn Charles L. , Addessi Elsa , Amici Federica , Anderson Rindy C. , Aureli Filippo , Baker Joseph M. , Bania Amanda E. , Barnard Allison M. , Boogert Neeltje J. , Brannon Elizabeth M. , Bray Emily E. , Bray Joel , Brent Lauren J. N. , Burkart Judith M. , Call Josep , Cantlon Jessica F. , Cheke Lucy G. , Clayton Nicola S. , Delgado Mikel M. , DiVincenti Louis J. , Fujita Kazuo , Herrmann Esther , Hiramatsu Chihiro , Jacobs Lucia F. , Jordan Kerry E. , Laude Jennifer R. , Leimgruber Kristin L. , Messer Emily J. E. , de A. Moura Antonio C. , Ostojić Ljerka , Picard Alejandra , Platt Michael L. , Plotnik Joshua M. , Range Friederike , Reader Simon M. , Reddy Rachna B. , Sandel Aaron A. , Santos Laurie R. , Schumann Katrin , Seed Amanda M. , Sewall Kendra B. , Shaw Rachael C. , Slocombe Katie E. , Su Yanjie , Takimoto Ayaka , Tan Jingzhi , Tao Ruoting , van Schaik Carel P. , Virányi Zsófia , Visalberghi Elisabetta , Wade Jordan C. , Watanabe Arii , Widness Jane , Young Julie K. , Zentall Thomas R. , Zhao Yini
Published: April 2014

Significance

Although scientists have identified surprising cognitive flexibility in animals and potentially unique features of human psychology, we know less about the selective forces that favor cognitive evolution, or the proximate biological mechanisms underlying this process. We tested 36 species in two problem-solving tasks measuring self-control and evaluated the leading hypotheses regarding how and why cognition evolves. Across species, differences in absolute (not relative) brain volume best predicted performance on these tasks. Within primates, dietary breadth also predicted cognitive performance, whereas social group size did not. These results suggest that increases in absolute brain size provided the biological foundation for evolutionary increases in self-control, and implicate species differences in feeding ecology as a potential selective pressure favoring these skills.