Magnetism in lithium-oxygen discharge product

Nonaqueous lithium-oxygen batteries have a much superior theoretical gravimetric energy density compared to conventional lithium-ion batteries, and thus could render long-range electric vehicles a reality. A molecular-level understanding of the reversible formation of lithium peroxide in these batteries, the properties of major/minor discharge products, and the stability of the nonaqueous electrolytes is required to achieve successful lithium-oxygen batteries. We demonstrate that the major discharge product formed in the lithium-oxygen cell, lithium peroxide, exhibits a magnetic moment. These results are based on dc-magnetization measurements and a lithium-oxygen cell containing an ether-based electrolyte. The results are unexpected because bulk lithium peroxide has a significant band gap. Density functional calculations predict that superoxide-type surface oxygen groups with unpaired electrons exist on stoichiometric lithium peroxide crystalline surfaces and on nanoparticle surfaces; these computational results are consistent with the magnetic measurement of the discharged lithium peroxide product as well as EPR measurements on commercial lithium peroxide. The presence of superoxide-type surface oxygen groups with spin can play a role in the reversible formation and decomposition of lithium peroxide as well as the reversible formation and decomposition of electrolyte molecules.

Molecular dynamics simulation of yttria-stabilized zirconia (YSZ) crystalline and amorphous solids

An empirically fitted atomic potential allows a classical molecular dynamics study of the static and dynamic properties of both crystalline and amorphous yttria-stabilized zirconia (YSZ) with typical dilute Y(2)O(3) concentrations (i.e. 3.0-12.0 mol% Y(2)O(3)) in the temperature range 300-1400 K. Based on the rigid ion model approximation, we find, regardless of the distinctly different geometries, that the oxygen ionic conductivity shows a maximum at ∼ 8.0 mol% Y(2)O(3), close to the experimental maximum. A lower absolute ionic conductivity is found for the high density YSZ amorphous solid, relative to crystalline YSZ, consistent with the trends observed in crystalline and stabilized amorphous thin films of YSZ reported in experiments. Different from YSZ crystals, intriguing features of mutual diffusion among the heavy cations and mobile anions are found in the amorphous phase.

Lattice dielectric and thermodynamic properties of yttria stabilized zirconia solids

A study of lattice dielectric and thermodynamic properties of yttria stabilized zirconia (YSZ) crystals as a function of yttria concentration is reported. This study is based on density functional perturbation theory, using ABINIT. Within the local density approximation and the harmonic approximation, we find excellent agreement between calculated and low temperature experimental specific heat and dielectric constants. From the variation of the specific heat of YSZ with the yttria composition, we propose a simple additivity rule that estimates the dependence of the specific heat of YSZ on the yttria concentration, whereas for the dielectric constants of YSZ, the values are bounded by the dielectric constants of cubic and amorphous zirconia.

Structure and stability of Mg-intercalated boron nanotubes and crystalline bundles

First principles calculations based on density functional theory predict a highly selective adsorption site for Mg atoms and negligible preference for the growth of Mg islands on the tubular surface of Mg-intercalated (small diameter) boron nanotubes, thereby establishing the criterion for understanding the growth mechanism of single-walled boron nanotubes (SWBNTs) supported by magnesium. On the other hand, the Mg-SWBNT bundles can be considered as an 'electrostatic' bound system consisting of partially ionized Mg and partially ionized tubules. The metallic character of the tubular Mg-B bundles is then attributed to boron atoms forming a metallic wire, while the role of Mg atoms is limited in enhancing the stability of the crystalline bundles.

Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl

The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH2BrCl) in the region of 85,320-88,200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0-1400 cm-1 above the adiabatic ionization energy (IE) of CH2BrCl, the Br-C-Cl bending vibration progression (nu1+=0-8) of CH2BrCl+ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400-2600 cm-1 above the IE(CH2BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH2BrCl+(A 2A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH2BrCl)=85,612.4+/-2.0 cm-1 (10.6146+/-0.0003 eV) and the bending frequencies nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->CH2Cl++Br+e-, in the energy range of 11.36-11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH2Cl+)=11.509+/-0.002 eV. Combining the 0 K AE(CH2Cl+) and IE(CH2BrCl) values obtained in this study, together with the known IE(CH2Cl), we have determined the 0 K bond dissociation energies (D0) for CH2Cl+-Br (0.894+/-0.002 eV) and CH2Cl-Br (2.76+/-0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH2BrCl), AE(CH2Cl+), IE(CH2Cl), D0(CH2Cl+-Br), and D0(CH2Cl-Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.

The 2D-3D structural transition and chemical bonding in elemental boron nanoclusters

The rich chemistry of boron compounds are often found dominated by its structural dimensionality and chemical bonding from which some of the qualitative features of boron clusters can easily be extracted. In this article, we review such features to discuss structural properties of Bn clusters. In both small-cluster regime of n ≤ 20 and largecluster regime of n ≥ 20, the preferred topological structures are the result of the interplay between bonding factors related to the delocalized π bonds and the inter-icosahedral and intra-icosahedral bonds. The bulk fragments of boron are also expected to become a competitive isomeric configuration with the increase in the cluster-size, in contrast to 3D spherical cages observed in the large carbon clusters

A high-resolution pulsed field ionization-photoelectron-photoion coincidence study of vinyl bromide

By employing the high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence method, we have examined the unimolecular dissociation reaction of energy-selected C(2)H(3)Br(+) to form C(2)H(3) (+)+Br near its threshold. The analysis of the breakdown curves for C(2)H(3)Br(+) and C(2)H(3) (+) yields a value of 11.9010+/-0.0015 eV for the 0 K dissociative photoionization threshold or appearance energy (AE) for C(2)H(3) (+) from C(2)H(3)Br. This AE(C(2)H(3) (+)) value, together with the ionization energy (IE) for C(2)H(3)Br (9.8200+/-0.0015 eV) obtained by PFI-PE and threshold photoelectron (TPE) measurements, has allowed the determination of the 0 K dissociation energy (D(0)) for the C(2)H(3) (+)-Br bond to be 2.081+/-0.002 eV. The 0 K AE(C(2)H(3) (+)) from C(2)H(3)Br obtained in this study corresponds to DeltaH(f0) ( composite function )(C(2)H(3) (+))=1123.7+/-1.9 kJ/mol. Combining the latter value and the known DeltaH(f0) ( composite function )(C(2)H(3))=306.7+/-2.1 kJ/mol, we calculated a value of 8.468+/-0.029 eV for the IE(C(2)H(3)), which is in accord with the result obtained in the previous photoionization efficiency study. We have also carried out high-level ab initio calculations for the IE(C(2)H(3)) at the Gaussian-3 and the CCSD(T,full)/CBS level of theory. The CCSD(T,full)/CBS prediction of 8.487 eV for the IE(C(2)H(3)-->bridged-C(2)H(3) (+)) is in good agreement with the IE(C(2)H(3)) value derived in the present experiment. Combining the 0 K AE(C(2)H(3) (+))=11.9010+/-0.0015 eV and the IE(C(2)H(3))=8.468+/-0.029 eV yields the value of 3.433+/-0.029 eV for D(0)(C(2)H(3)-Br). We have also recorded the TPE spectrum of C(2)H(3)Br in the energy range of 9.80-12.20 eV. Members (n=5-14) of four autoionizing Rydberg series converging to the C(2)H(3)Br(+)(A (2)A(')) state are observed in the TPE spectrum. The analysis of the converging limit of these Rydberg series and the vibrational TPE bands for C(2)H(3)Br(+)(A (2)A(')) has provided more precise values for the nu(6) (+) (1217+/-10 cm(-1)) and nu(8) (+) (478+/-8 cm(-1)) modes and the IE (10.9156+/-0.0010 eV) for the formation of C(2)H(3)Br(+)(A (2)A(')) from C(2)H(3)Br.

Rovibrational-state-selected photoionization of acetylene by the two-color IR+VUV scheme: observation of rotationally resolved Rydberg transitions

We have demonstrated a rovibrational-state-selected photoionization experiment using an IR laser and high-resolution VUV-synchrotron radiation. The VUV photoionization of acetylene [C2H2(Xtilde; (1)Sigma(+)(g);nu(3)=1,J(')=8 or 10)] prepared by IR excitation reveals three strong autoionizing Rydberg series converging to C2H+2(Xtilde; (2)Pi(u);nu(+)(3)=1) with little ion background interference. Rotational transitions resolved for the Rydberg states provide an estimate of approximately 1.8 ps for their lifetimes. This experiment opens the way for state-selective photoionization studies of polyatomic molecules using VUV-synchrotron radiation.

Preliminary evaluation of "interpreter" role plays in teaching communication skills to medical undergraduates

RATIONALE AND OBJECTIVES

Multiculturalism presents linguistic obstacles to health care provision. We explored the early introduction of "interpreter" role-play exercises in teaching medical undergraduates communication skills. The interpreter role creates a natural barrier in communication providing an active prompt for recognizing learning needs in this area.

METHODS

Bilingual Cantonese first-year medical students (n=160) were randomly allocated to either "Observer" or "Interpreter" role plays at a small-group introductory communication skills workshop using a quasi experimental design, counterbalanced across tutors. Students assessed their own skill competence before and, together with their perceptions of the different role plays' effectiveness, again after the workshop, using an anonymous 16 item Likert-type scale, analysed using ANOVA and MANOVA.

RESULTS

Students' assessments of their skills improved significantly following the workshop (F=73.19 [1,156], P=0.0009). Students in the observer group reported greater changes in their scores following the workshop than did students in the interpreter group (F=4.84 [1,156], P=0.029), largely due to improvement in perceived skill (F=4.38 [1,156], P=0.038) rather than perceived programme effectiveness (F=3.13 [1,156], P > 0.05). Subsequent MANOVA indicated no main effect of observer/interpreter conditions, indicating these differences could be attributed to chance alone (F=1.41 [16 141], P > 0.05).

CONCLUSION

The workshop positively influenced students' perceived communication skills, but the "Interpreter" role was less effective than the "Observer" role in achieving this. Future studies should examine whether interpreter role plays introduced later in the medical programme are beneficial.

Successful radiofrequency ablation in an infant with drug-resistant permanent junctional reciprocating tachycardia

Over the past decade, the technique of radiofrequency ablation has evolved substantially. Currently, most forms of cardiac arrhythmias seen in children can be treated with good long-term results and low risk of adverse outcome. Curative arrhythmia treatment with this technique, however, is still uncommon in neonates and infants. Reported here is our experience in the management of an 8-week-old with drug-resistant permanent junctional reciprocating tachycardia.

Simplified single patch technique for the repair of atrioventricular septal defect

OBJECTIVE

Because of the complexity of traditional 1- and 2-patch techniques for the repair of complete atrioventricular septal defect, we modified our repair technique to avoid the use of any ventricular septal patch material. We report our prospective experience with this simplified 1-patch technique.

METHOD

Forty-seven consecutive patients between May 1995 and August 1998 underwent repair with the use of this technique without modification. Repair was done in all patients by direct suturing of the common atrioventricular valve leaflets to the crest of the ventricular septum. No division of valve leaflets was necessary. A single pericardial patch was used to close the defect in the atrial septal component. Follow-up included electrocardiography and echocardiographic assessment of ventricular function, atrioventricular valve function, and adequacy of the left ventricular outflow tract.

RESULTS

There were 2 deaths (4%), only 1 cardiac related, in the series. There were 17 male patients and 30 female patients. Mean age at repair was 5.6 months (median, 3.4 months). Associated lesions were repaired in 19 patients (40%). Mean follow-up was 1.85 years (median, 1.9 years). There was no heart block. There were no significant residual ventricular septal defects detected and no left ventricular outflow tract obstruction seen on echocardiography in any patient to date. Mitral valve status after operation was assessed as no incompetence in 13 patients (28%), minimal in 19 patients (40%), mild in 12 patients (26%), and moderate in 3 patients (6%).

CONCLUSION

The repair of complete atrioventricular septal defect by direct suturing of the atrioventricular valve leaflets to the crest of the ventricular septum with a single-patch technique greatly simplifies the repair and does not lead to left ventricular outflow tract obstruction nor interfere with valve function.

Supraventricular electrical interaction in conjoined twins with common coronary sinus

Conjoined twins with echocardiographic evidence of continuity of the coronary sinuses had identical heart rates on ECG. Both had broad, polyphasic QRS complexes, and various imaging modalities were unable to determine whether there was ventricular myocardial continuity. Administration of adenosine demonstrated that the broad polyphasic complexes were a "fusion" of the twins' individual QRS complexes, which could be clearly distinguished after administration of the drug. Ventricular pacing resulted in dissociation of the individual QRS complexes, thus demonstrating an absence of ventricular myocardial continuity. This was confirmed when the twins were successfully separated at the age of 10 months.

Radiofrequency catheter ablation in a haemodynamically compromised premature neonate with hydrops fetalis

A preterm infant was born at 35 weeks gestation after failed antenatal antiarrhythmic therapy. The infant had an incessant supraventricular tachycardia, impaired ventricular function and hypotension and failed to respond to adenosine, cardioversion and intravenous amiodarone. After resuscitation from cardiovascular collapse, a successful radiofrequency catheter ablation (RFA) of a left free wall atrioventricular pathway was performed at 24 h of age without extracorporeal support. The infant is normal on follow up at 12 months of age. Whilst most fetal and neonatal supraventricular tachyarrhythmias respond to antiarrhythmic medications and RFA is not required, this is the earliest RFA to be performed on a premature infant when antiarrhythmics have failed.

Radiofrequency catheter ablation of right ventricular outflow tract tachycardia in a preschooler

A 3-year-old girl presented with a febrile illness complicated by right ventricular outflow tract tachycardia, which persisted after resolution of the presumed viral infection. The tachycardia was intermittent, but was significantly exacerbated by exercise. Radiofrequency ablation (RFA) of the ectopic focus was successfully performed and the child remains free of tachycardia 12 months later. A review of the literature suggests that RFA in children is increasingly seen as a safe and convenient option for the treatment of supraventricular tachycardia, whereas the management of ectopic ventricular tachycardia in pediatric practice has not been well defined.

Adenosine in the management of supraventricular tachycardia in children

OBJECTIVE

To assess the efficacy and safety of adenosine in the management of supraventricular tachycardia in children.

METHODOLOGY

A review of 43 children with supraventricular tachycardia who received intravenous adenosine between June 1992 and July 1995.

RESULTS

Thirty-five patients had re-entrant supraventricular tachycardia and eight patients had atrial tachydysrhythmias. Reversion to sinus rhythm occurred in 75% of episodes in all patients treated for supraventricular tachycardia, and in 96% of episodes in patients with re-entrant supraventricular tachycardia. Early re-initiation of supraventricular tachycardia after reversion to sinus rhythm occurred in 25% of episodes. Sixteen percent of patients reverted with the recommended 0.05 mg/kg starting dose, and 35% reverted with a dose of 0.1 mg/kg. Four patients were given adenosine as a diagnostic procedure to elicit occult pre-excitation. The most common side effects were brief feelings of discomfort. No serious side effects occurred.

CONCLUSION

Adenosine is safe and effective in the management of supraventricular tachycardia in children. A commencing dose of 0.1 mg/kg is appropriate.