Large Fermi surface in pristine kagome metal CsV3Sb5 and enhanced quasiparticle effective masses

The kagome metal CsV[Formula: see text]Sb[Formula: see text] is an ideal platform to study the interplay between topology and electron correlation. To understand the fermiology of CsV[Formula: see text]Sb[Formula: see text], intensive quantum oscillation (QO) studies at ambient pressure have been conducted. However, due to the Fermi surface reconstruction by the complicated charge density wave (CDW) order, the QO spectrum is exceedingly complex, hindering a complete understanding of the fermiology. Here, we directly map the Fermi surface of the pristine CsV[Formula: see text]Sb[Formula: see text] by measuring Shubnikov-de Haas QOs up to 29 T under pressure, where the CDW order is completely suppressed. The QO spectrum of the pristine CsV[Formula: see text]Sb[Formula: see text] is significantly simpler than the one in the CDW phase, and the detected oscillation frequencies agree well with our density functional theory calculations. In particular, a frequency as large as 8,200 T is detected. Pressure-dependent QO studies further reveal a weak but noticeable enhancement of the quasiparticle effective masses on approaching the critical pressure where the CDW order disappears, hinting at the presence of quantum fluctuations. Our high-pressure QO results reveal the large, unreconstructed Fermi surface of CsV[Formula: see text]Sb[Formula: see text], paving the way to understanding the parent state of this intriguing metal in which the electrons can be organized into different ordered states.

Nodeless Superconductivity in Kagome Metal CsV3Sb5 with and without Time Reversal Symmetry Breaking

The kagome metal CsV₃Sb₅ features an unusual competition between the charge-density-wave (CDW) order and superconductivity. Evidence for time reversal symmetry breaking (TRSB) inside the CDW phase has been accumulating. Hence, the superconductivity in CsV₃Sb₅ emerges from a TRSB normal state, potentially resulting in an exotic superconducting state. To reveal the pairing symmetry, we first investigate the effect of nonmagnetic impurity. Our results show that the superconducting critical temperature is insensitive to disorder, pointing to conventional s-wave superconductivity. Moreover, our measurements of the self-field critical current (I_c,sf), which is related to the London penetration depth, also confirm conventional s-wave superconductivity with strong coupling. Finally, we measure I_c,sf where the CDW order is removed by pressure and superconductivity emerges from the pristine normal state. Our results show that s-wave gap symmetry is retained, providing strong evidence for the presence of conventional s-wave superconductivity in CsV₃Sb₅ irrespective of the presence of the TRSB.

Patterned diamond anvils prepared via laser writing for electrical transport measurements of thin quantum materials under pressure

Quantum materials exhibit intriguing properties with important scientific values and huge technological potential. Electrical transport measurements under hydrostatic pressure have been influential in unraveling the underlying physics of many quantum materials in bulk form. However, such measurements have not been applied widely to samples in the form of thin flakes, in which new phenomena can emerge, due to the difficulty in attaching fine wires to a thin sample suitable for high-pressure devices. Here, we utilize a home-built direct laser writing system to functionalize a diamond anvil to directly integrate the capability of conducting electrical transport measurements of thin flakes with a pressure cell. With our methodology, the culet of a diamond anvil is equipped with a set of custom-designed conducting tracks. We demonstrate the superiority of these tracks as electrodes for the studies of thin flakes by presenting the measurement of pressure-enhanced superconductivity and quantum oscillations in a flake of MoTe₂.

Pressure-induced enhancement of the superconducting transition temperature in La2O2Bi3AgS6

Charge density wave (CDW) instability is often found in phase diagrams of superconductors such as cuprates and certain transition-metal dichalcogenides. This proximity to superconductivity triggers the question on whether CDW instability is responsible for the pairing of electrons in these superconductors. However, this issue remains unclear and new systems are desired to provide a better picture. Here, we report the temperature-pressure phase diagram of a recently discovered BiS₂superconductor La₂O₂Bi₃AgS₆, which shows a possible CDW transition atT* ∼ 155 K and a superconducting transition atT_c∼ 1.0 K at ambient pressure, via electrical resistivity measurements. Upon applying pressure,T* decreases linearly and extrapolates to 0 K at 3.9 GPa. Meanwhile,T_cis enhanced and reaches maximum value of 4.1 K at 3.1 GPa, forming a superconducting dome in the temperature-pressure phase diagram.

Fragile Pressure-Induced Magnetism in FeSe Superconductors with a Thickness Reduction

The emergence of high transition temperature (T_c) superconductivity in bulk FeSe under pressure is associated with the tuning of nematicity and magnetism. However, sorting out the relative contributions from magnetic and nematic fluctuations to the enhancement of T_c remains challenging. Here, we design and conduct a series of high-pressure experiments on FeSe thin flakes. We find that as the thickness decreases the nematic phase boundary on temperature-pressure phase diagrams remains robust while the magnetic order is significantly weakened. A local maximum of T_c is observed outside the nematic phase region, not far from the extrapolated nematic end point in all samples. However, the maximum T_c value is reduced associated with the weakening of magnetism. No high-T_c phase is observed in the thinnest sample. Our results strongly suggest that nematic fluctuations alone can only have a limited effect while magnetic fluctuations are pivotal on the enhancement of T_c in FeSe.

Detection of Hole Pockets in the Candidate Type-II Weyl Semimetal MoTe_{2} from Shubnikov-de Haas Quantum Oscillations

The bulk electronic structure of T_{d}-MoTe_{2} features large hole Fermi pockets at the Brillouin zone center (Γ) and two electron Fermi surfaces along the Γ-X direction. However, the large hole pockets, whose existence has important implications for the Weyl physics of T_{d}-MoTe_{2}, has never been conclusively detected in quantum oscillations. This raises doubt about the realizability of Majorana states in T_{d}-MoTe_{2}, because these exotic states rely on the existence of Weyl points, which originated from the same band structure predicted by density functional theory (DFT). Here, we report an unambiguous detection of these elusive hole pockets via Shubnikov-de Haas (SdH) quantum oscillations. At ambient pressure, the quantum oscillation frequencies for these pockets are 988 and 1513 T, when the magnetic field is applied along the c axis. The quasiparticle effective masses m^{*} associated with these frequencies are 1.50 and 2.77 m_{e}, respectively, indicating the importance of Coulomb interactions in this system. We further measure the SdH oscillations under pressure. At 13 kbar, we detected a peak at 1798 T with m^{*}=2.86m_{e}. Relative to the oscillation data at a lower pressure, the amplitude of this peak experienced an enhancement, which can be attributed to the reduced curvature of the hole pockets under pressure. Combining our experimental data with DFT+U calculations, where U is the Hubbard parameter, our results shed light on why these important hole pockets have not been detected until now.

Measuring magnetic field texture in correlated electron systems under extreme conditions

Pressure is a clean, continuous, and systematic tuning parameter among the competing ground states in strongly correlated electron systems such as superconductivity and magnetism. However, owing to the restricted access to samples enclosed in high-pressure devices, compatible magnetic field sensors with sufficient sensitivity are rare. We used nitrogen vacancy centers in diamond as a spatially resolved vector field sensor for material research under pressure at cryogenic temperatures. Using a single crystal of BaFe2(As0.59P0.41)2 as a benchmark, we extracted the superconducting transition temperature, the local magnetic field profile in the Meissner state, and the critical fields. The method developed in this work offers a distinct tool for probing and understanding a range of quantum many-body systems.

Maximizing T c by tuning nematicity and magnetism in FeSe1-x S x superconductors

A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature (T c). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving non-magnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature (T) against pressure (P) and isovalent S-substitution (x), for FeSe1-x S x . By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended non-magnetic tetragonal phase emerges, where T c shows a striking enhancement. The completed phase diagram uncovers that high-T c superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas T c remains low near the nematic critical point.

Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron–electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations.

The electronic structure of the helimagnet CrAs is unusual due to its nonsymmorphic crystal symmetry. Here, the authors observe quasilinear magnetoresistance close to a pressure-driven superconducting transition, which may arise from the interaction of the band structure and magnetic fluctuations.

From Kondo lattices to Kondo superlattices

The realization of new classes of ground states in strongly correlated electron systems continues to be a major issue in condensed matter physics. Heavy fermion materials, whose electronic structure is essentially three-dimensional, are one of the most suitable systems for obtaining novel electronic states because of their intriguing properties associated with many-body effects. Recently, a state-of-the-art molecular beam epitaxy technique was developed to reduce the dimensionality of heavy electron systems by fabricating artificial superlattices that include heavy fermion compounds; this approach can produce a new type of electronic state in two-dimensional (2D) heavy fermion systems. In artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3, the magnetic order is suppressed by a reduction in the thickness of the CeIn3 layers. In addition, the 2D confinement of heavy fermions leads to enhancement of the effective electron mass and deviation from the standard Fermi liquid electronic properties, which are both associated with the dimensional tuning of quantum criticality. In the superconducting superlattices of the heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, signatures of superconductivity are observed even at the thickness of one unit-cell layer of CeCoIn5. The most remarkable feature of this 2D heavy fermion superconductor is that the thickness reduction of the CeCoIn5 layers changes the temperature and angular dependencies of the upper critical field significantly. This result is attributed to a substantial suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking at the interfaces of CeCoIn5 block layers. The importance of the inversion symmetry breaking in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy, which can resolve spectroscopic information from each layer separately, even within the same CeCoIn5 block layer. In addition, recent experiments involving CeCoIn5/YbCoIn5 superlattices have shown that the degree of the inversion symmetry breaking and, in turn, the Rashba splitting are controllable, offering the prospect of achieving even more fascinating superconducting states. Thus, these Kondo superlattices pave the way for the exploration of unconventional metallic and superconducting states.

Robust two-dimensional superconductivity and vortex system in Bi2Te3/FeTe heterostructures

The discovery of two-dimensional superconductivity in Bi2Te3/FeTe heterostructures provides a new platform for the search of Majorana fermions in condensed matter systems. Since Majorana fermions are expected to reside at the core of the vortices, a close examination of the vortex dynamics in superconducting interface is of paramount importance. Here, we report the robustness of the interfacial superconductivity and 2D vortex dynamics in four as-grown and aged Bi2Te3/FeTe heterostructure with different Bi2Te3 epilayer thickness (3, 5, 7, 14 nm). After two years' air exposure, superconductivity remains robust even when the thickness of Bi2Te3 epilayer is down to 3 nm. Meanwhile, a new feature at ~13 K is induced in the aged samples, and the high field studies reveal its relevance to superconductivity. The resistance of all as-grown and aged heterostructures, just below the superconducting transition temperature follows the Arrhenius relation, indicating the thermally activated flux flow behavior at the interface of Bi2Te3 and FeTe. Moreover, the activation energy exhibits a logarithmic dependence on the magnetic field, providing a compelling evidence for the 2D vortex dynamics in this novel system. The weak disorder associated with aging-induced Te vacancies is possibly responsible for these observed phenomena.

Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (Ca(x)Sr(1-x))₃Rh₄Sn₁₃

The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.

Ambient pressure structural quantum critical point in the phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13)

The quasiskutterudite superconductor Sr_{3}Rh_{4}Sn_{13} features a pronounced anomaly in electrical resistivity at T^{*}∼138  K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T^{*} as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., x_{c}=0.9). This establishes the (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures.

Controllable Rashba spin-orbit interaction in artificially engineered superlattices involving the heavy-fermion superconductor CeCoIn5

By using a molecular beam epitaxy technique, we fabricate a new type of superconducting superlattices with controlled atomic layer thicknesses of alternating blocks between the heavy-fermion superconductor CeCoIn5, which exhibits a strong Pauli pair-breaking effect, and nonmagnetic metal YbCoIn5. The introduction of the thickness modulation of YbCoIn5 block layers breaks the inversion symmetry centered at the superconducting block of CeCoIn5. This configuration leads to dramatic changes in the temperature and angular dependence of the upper critical field, which can be understood by considering the effect of the Rashba spin-orbit interaction arising from the inversion symmetry breaking and the associated weakening of the Pauli pair-breaking effect. Since the degree of thickness modulation is a design feature of this type of superlattices, the Rashba interaction and the nature of pair breaking are largely tunable in these modulated superlattices with strong spin-orbit coupling.

Nuclear magnetic resonance at up to 10.1 GPa pressure detects an electronic topological transition in aluminum metal

High-sensitivity (27)Al nuclear magnetic resonance (NMR) measurements of aluminum metal under hydrostatic pressure of up to 10.1 GPa reveal an unexpected negative curvature in the pressure dependence of the electronic density of states measured through shift and relaxation, which violates free electron behavior. A careful analysis of the Fermiology of aluminum shows that pressure induces an electronic topological transition (Lifshitz transition) that is responsible for the measured change in the density of states. The experiments also reveal a sudden increase in the NMR linewidth above 4.2 GPa from quadrupole interaction, which is not in agreement with the metal's cubic symmetry.

Pressure- and composition-induced structural quantum phase transition in the cubic superconductor (Sr, Ca)3Ir4Sn13

We show that the quasi-skutterudite superconductor Sr(3)Ir(4)Sn(13) undergoes a structural transition from a simple cubic parent structure, the I phase, to a superlattice variant, the I' phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T(*) can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.

Anomalous upper critical field in CeCoIn5/YbCoIn5 superlattices with a Rashba-type heavy Fermion interface

We report a highly unusual angular variation of the upper critical field (H(c2)) in epitaxial superlattices CeCoIn(5)(n)/YbCoIn(5)(5), formed by alternating layers of n and a 5 unit-cell thick heavy-fermion superconductor CeCoIn(5) with a strong Pauli effect and normal metal YbCoIn(5), respectively. For the n=3 superlattice, H(c2)(θ) changes smoothly as a function of the field angle θ. However, close to the superconducting transition temperature, H(c2)(θ) exhibits a cusp near the parallel field (θ=0°). This cusp behavior disappears for n=4 and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the n=3 superlattice, which may be due to the suppression of the Pauli effect in a system with local inversion symmetry breaking. Taking into account the temperature dependence of H(c2)(θ) as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields.

Distribution of atypical fractures and cortical stress lesions in the femur: implications on pathophysiology

INTRODUCTION

Some authors have hypothesised that atypical femur fractures occur due to tensile mechanism of failure. We studied the distribution of such lesions along the femur shaft to determine if they concentrate in regions that are subject to tensile loading.

METHODS

From May 2004 to March 2010, radiological reviews of 48 patients aged 69 +/- 10.4 (range 47-92) years with atypical femoral fractures and lesions were performed. The absolute distance of each lesion from the greater trochanter and the ratio of the distance of each lesion from the greater trochanter expressed as a percentage of the entire femur length were measured.

RESULTS

All periosteal reactions and cortical stress lesions occurred in the lateral cortex. There were 35 right femoral lesions (28 complete fractures and seven cortical stress reactions), with a median distance of 108.3 +/- 54.0 (range 67.0-270.4) mm from the greater trochanter and a median ratio of 23.9 +/- 11.7 (range 15.7-58.6) percent of the entire femoral length. There were 38 left femoral lesions (27 complete fractures and 11 cortical stress reactions), with a median distance of 109.9 +/- 43.1 (range 73.6-246.2) mm from the greater trochanter and a median ratio of 24.4 +/- 9.1(range 16.3-51.1) percent of the entire femoral length.

CONCLUSION

Based on previously established femoral shaft loading characteristics, atypical lesions were clustered at the region of maximal tensile loading. No lesion occurred in regions that were subject to compressive loading. This unique distribution supports a tensile mechanism of failure in such lesions.

Quantum oscillations in the anomalous phase in Sr3Ru2O7

We report measurements of quantum oscillations detected in the putative nematic phase of Sr3Ru2O7. Improvements in sample purity enabled the resolution of small amplitude de Haas-van Alphen (dHvA) oscillations between two first order metamagnetic transitions delimiting the phase. Two distinct frequencies were observed, whose amplitudes follow the normal Lifshitz-Kosevich profile. Variations of the dHvA frequencies are explained in terms of a chemical potential shift produced by reaching a peak in the density of states, and an anomalous field dependence of the oscillatory amplitude provides information on domains.

High sensitivity nuclear magnetic resonance probe for anvil cell pressure experiments

While the highest pressures can be achieved with diamond anvil cells, limited sample size and anvil geometry have hampered their application in nuclear magnetic resonance (NMR) experiments due to weak signal-to-noise. Here we report a new probe design that is based on having the resonant radio frequency coil that encloses the sample within the anvil cell inside the gasket hole. This increases the filling factor tremendously and results in greatly enhanced NMR sensitivity. The setup is described together with room temperature Na and Al NMR experiments.

Microarray analysis of multiple candidate genes and associated plasma proteins for nephropathy secondary to type 2 diabetes among Chinese individuals

AIMS/HYPOTHESIS

Evolving research suggests that common and rare alleles jointly constitute the genetic landscape of complex disease. We studied the association between 43 pathway-related candidate genes with 'intermediate phenotype' (i.e. corresponding plasma protein) and diabetic nephropathy in a customised microarray of 1,536 SNPs.

METHODS

In this case-control study of type 2 diabetic Chinese individuals with and without diabetic nephropathy, cases (n = 545) were defined on the basis of a spot urinary albumin/creatinine ratio (ACR) > 113 mg/mmol; the value for controls (n = 503) was ACR < 3.3 mg/mmol. Genotyping was performed using Illumina GoldenGate assay.

RESULTS

No single nucleotide polymorphism (SNP) remained significant in single locus analysis after correction for multiple testing. Therefore, we explored the best approximately 1% SNPs. Of these 13 SNPs, four clustered to a 5' end NADPH oxidase homologue 4 (NOX4) haplotype (GGCC frequency = 0.776) with estimated OR for diabetic nephropathy of 2.05 (95% CI 1.04-4.06) (heterozygous) and 2.48 (1.27-4.83) (homozygous) (p = 0.0055). The haplotype was correlated with plasma Cu/Zn superoxide dismutase (SOD) concentration, suggesting increased oxidative burden. Endothelin-1 SNP (rs1476046G>A, frequency = 0.252) was correlated with plasma C-terminal pro-endothelin-1 concentrations with an estimated OR for diabetic nephropathy of (heterozygous) 1.26 (0.96-1.66) and (homozygous) 1.87 (1.13-3.12) (p = 0.0072). Nitric oxide synthase 1 (NOS1) 5' haplotype (TGTC frequency = 0.38) also revealed a suggestive association with diabetic nephropathy: heterozygous 1.26 (0.95-1.67), homozygous 1.57 (1.04-2.35) (p = 0.0073). A rare NADPH oxidase homologue 1 (NOX1)-coding non-synonymous SNP (Arg315His, frequency = 0.006) was found exclusively among cases.

CONCLUSIONS/INTERPRETATION

Our preliminary observations suggest that common haplotypes from NOX4 and endothelin-1 SNP correlated with plasma Cu/Zn SOD and C-terminal pro-endothelin-1 concentrations, respectively, and might have conferred diabetic nephropathy susceptibility. Common NOS1 and rare NOX1 variants also revealed a suggestive association with diabetic nephropathy. Future studies to validate our observation are needed.

Exclusion of acute pulmonary embolism: computed tomography pulmonary angiogram or D-dimer?

INTRODUCTION

The aim of our study was to determine the accuracy of the D-dimer test in the exclusion of pulmonary embolism.

METHODS

In 2006, 446 patients at our hospital underwent computed tomography pulmonary angiogram (CTPA) for the exclusion of pulmonary embolism. We selected patients with a clinical suspicion of pulmonary embolism, and who underwent both a CTPA examination and a D-dimer test performed within a period of five days. Pregnant women, patients with an allergy to intravenous contrast and those who were on anticoagulant therapy were excluded. Based on our criteria, 219 cases were selected. D-dimer test was performed using an immunoturbidimetric assay. A cut-off value of 500 ng/ml was selected as the upper limit to exclude thrombosis.

RESULTS

There were 42 patients positive for pulmonary embolism on CTPA and all had elevated D-dimer values. There were 177 patients negative for pulmonary embolism on CTPA and 49 of them had normal D-dimer values. The sensitivity and specificity of the D-dimer test was 100.0 percent (95 percent confidence interval [CI] 91.6-100.0) and 27.7 percent (95 percent CI 21.2-34.9), respectively. The likelihood ratio for a positive test and negative test was 1.38 and 0, respectively.

CONCLUSION

The D-dimer test is suitable for screening patients with a clinical suspicion of pulmonary embolism. The indiscriminate use of CTPA results in unnecessary testing and elevates healthcare costs. Clinicians are urged to give due consideration to a D-dimer test result prior to requesting a CTPA examination.

Fermi-surface reconstruction in CeRh1-xCoxIn5

The evolution of the Fermi surface of CeRh(1-x)CoxIn5 was studied as a function of Co concentration x via measurements of the de Haas-van Alphen effect. By measuring the angular dependence of quantum oscillation frequencies, we identify a Fermi-surface sheet with f-electron character which undergoes an abrupt change in topology as x is varied. Surprisingly, this reconstruction does not occur at the quantum critical concentration x(c), where antiferromagnetism is suppressed to T=0. Instead we establish that this sudden change occurs well below x(c), at the concentration x approximately 0.4, where long-range magnetic order alters its character and superconductivity appears. Across all concentrations, the cyclotron effective mass of this sheet does not diverge, suggesting that critical behavior is not exhibited equally on all parts of the Fermi surface.

Knee locking secondary to osteochondral fracture of the patella: an unusual presentation

Acute locking is a sign of internal derangement of the knee and is an orthopaedic surgical emergency. Differential diagnoses of this condition are torn meniscus, intra-articular loose bodies and torn anterior cruciate ligament. We present a 15-year-old schoolboy who developed acute locking of the knee during dancing. Arthroscopy revealed that he had sustained an osteochondral fracture of the patella and the loose fragment from it caused locking of the knee. That this was not pseudo-locking was confirmed by examination of the knee under anaesthesia. Locking of the knee by a loose osteochondral fragment following acute dislocation of the patella, though rare, should be considered as a possible cause of true locking.

Angiotensin receptor antagonist vs. angiotensin-converting enzyme inhibitor in Asian subjects with type 2 diabetes and albuminuria - a randomized crossover study

BACKGROUND

Subjects with type 2 diabetes mellitus (T2DM) and albuminuria are at risk for progressive diabetic nephropathy. The relative blood pressure lowering and antialbuminuric efficacy of angiotensin receptor antagonist (ARB) vs. angiotensin-converting enzyme (ACE) inhibitor has not been well studied.

METHODS

Forty-one ARB- and ACE inhibitor-naive T2DM subjects with albuminuria (>30 mg/g creatinine) were given either 50 mg of losartan (ARB) or 20 mg of quinapril (ACE inhibitor) (50% maximum dose) for 4 weeks, with a 4-week wash-out period in-between interventions in a crossover fashion. The order of intervention was randomized. The primary endpoint was the reduction of blood pressure and albuminuria. Secondary endpoint was changes in plasma transforming growth factor beta (TGF-beta).

RESULTS

Among the 41 subjects, 66% were male. The mean age (s.d.) was 52 (10) years, and duration of diabetes was 8 (14) years. Blood pressure reduction (though not statistically significant) was similar on both interventions [systolic: losartan 3 (15) vs. quinapril 2 (13) mmHg, p = 0.52; diastolic: losartan 1 (9) vs. quinapril 2 (8) mmHg, p = 0.55]. However, amelioration of albuminuria [mean (s.e.)] was significantly greater with losartan [losartan vs. quinapril: -93 (82) vs. -49 (65) mg/g, p = 0.02]. There was no change in plasma TGF-beta levels [mean (s.d.)] on either treatment, losartan [before 12.1 (8.9) vs. after 11.9 (9.6) ng/ml, p = 0.68] and quinapril [11.1 (7.9) vs. 11.1 (7.8) ng/ml, p = 0.87).

CONCLUSION

In Asian subjects with T2DM and albuminuria, 4 weeks of losartan therapy at 50 mg daily appeared to have greater antialbuminuric effect than 20 mg of quinapril.

Oxidative burden in prediabetic and diabetic individuals: evidence from plasma coenzyme Q(10)

AIM

Individuals with diabetes and prediabetes are at risk of vascular injury. However, the exact mechanisms are unclear. The mitochondria mobile electron carrier coenzyme Q(10) (CoQ(10)) is a potent lipophilic antioxidant. We hypothesize that oxidative stress, detectable as changes in plasma CoQ(10) concentrations and composition, plays an important role in vascular disease in diabetes.

METHODS

We measured plasma CoQ(10) concentrations (including reduced ubiquinol and oxidized ubiquinone subfractions) in 60 subjects with normal glucose tolerance [NGT; fasting plasma glucose (FPG) < 5.5 mmol/l], 63 with impaired fasting glucose (IFG; FPG 5.6-6.9 mmol/l) and 69 with Type 2 diabetes (DM; FPG > 6.9 mmol/l).

RESULTS

In men and women, the total CoQ(10)/total cholesterol ratio was reduced in DM (mean +/-sd) [male (M) 0.09 +/- 0.04; female (F) 0.07 +/- 0.04] compared with NGT (0.29 +/- 0.08; 0.21 +/- 0.07) and IFG (0.27 +/- 0.07; 0.23 +/- 0.07) (DM vs. NGT and IFG P = 0.001). A stepwise reduction in the plasma ubiquinol fraction (ubiquinol/total CoQ10) was observed from NGT (M 0.93 +/- 0.06; F 0.95 +/- 0.06) compared with IFG (0.43 +/- 0.25; 0.41 +/- 0.15) and DM (0.24 +/- 0.11; F 0.29 +/- 0.16) (DM vs. IFG vs. NGT P = 0.001). In contrast, the plasma ubiquinone/ubiquinol ratio increased from NGT (M 0.08 +/- 0.07, F 0.06 +/- 0.08) to IFG (2.14 +/- 1.84, 1.75 +/- 1.04) to DM (4.77 +/- 4.88, 3.81 +/- 3.71) (DM vs. IFG vs. NGT P = 0.001). These differences remained after adjusting for age, body mass index and FPG.

CONCLUSIONS

The change in CoQ(10) with increasing FPG concentration suggests an increase in oxidative burden, already evident in the prediabetic IFG individuals. This increase in oxidative stress might contribute to the increased risk of vascular disease.

Relationship between common functional polymorphisms of the p22phox gene (-930A > G and +242C > T) and nephropathy as a result of Type 2 diabetes in a Chinese population

OBJECTIVE

Genetic determinants are important in diabetic nephropathy (DN). Oxidative stress has also emerged as an important pathogenic factor in DN and vascular NADH oxidase is a major source of reactive oxygen species (ROS). Previous small studies reported a strong but contradictory association between functional genetic variation of p22(phox), an important subcomponent of NADH oxidase, and DN. We investigated the association between two common functional single nucleotide polymorphisms (SNPs) (-930 A > G and +242 C > T) and DN in a much larger group of Chinese patients with Type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

Case-control study of Chinese subjects with long-standing T2DM (> 10 years). Cases (n = 306) were subjects with a spot urinary albumin : creatinine ratio (ACR) of > 113 mg/mmol or elevated serum creatinine. Control subjects (n = 306) had ACR < 3.3 mg/mmol and normal serum creatinine. Genotyping was carried out by standard PCR and restriction fragment length polymorphism analysis.

RESULTS

Gender distribution, age, duration of diabetes and HbA(1c) were similar in cases and control subjects. Distribution of genotypes in the control subjects for both SNPs was consistent with the Hardy-Weinberg equilibrium. Distribution of genotypes did not differ significantly between cases and control subjects for both polymorphisms-+2424C > T: cases CC 84.6%, CT 15.0%, TT 0.4% and control subjects CC 87.6%, CT 11.8%, TT 0.6% (P = 0.45); -930 A > G: cases AA 40.5%, AG 41.8%, GG 17.7% and control subjects AA 38.2%, AG 49.0%, GG 12.8% (P = 0.12). Distribution of alleles was also similar-+2424 C > T: cases C 92.2%, T 7.8% and control subjects C 93.5%, T 6.5% (P = 0.66); -930 A > G cases A 61.4%, G 38.6% and control subjects A 62.7%, G 37.3% (P = 0.38). We estimated that our study has approximately 80% power to detect a relative risk of 1.65 (for +242 C > T) and 1.35 (for -930 A > G) conferred by the minor allele, respectively.

CONCLUSIONS

In contrast with previous small studies, our data suggest that these SNPs do not confer significantly increased susceptibility to DN secondary to T2DM in Chinese subjects.

Childhood acute pancreatitis in a children's hospital

OBJECTIVE

To analyse the cases of acute pancreatitis presented to a children's hospital in Singapore.

METHODS

Clinical charts of all children, aged under 18 years, who presented to our hospital for the first time with pancreatitis (ICD search criteria = 577.x) between the period of 1998 and mid-2002 were reviewed. Parameters analysed included presenting features, aetiology of the acute pancreatitis, length of hospital stay, complications, treatment and outcome.

RESULTS

There were 12 cases in the review period, and the attributable causes in these cases were, in descending order, trauma, drug-induced, anatomical anomalies, poisoning and idiopathic. Of interest were two patients whose pancreatitis were results of child abuse. The most common symptoms were abdominal pain (n=11) and vomiting (n=7), though only five patients localised the pain to the epigastrium. Abdominal tenderness could be elicited in all the patients. Eleven had evidence of acute pancreatitis from computerised tomography (CT) whilst the twelfth was diagnosed with ultrasonography. The peak amylase levels amongst these patients were not high, with a median of 512.5 U/L. In the acute stage, only one patient required operative intervention whilst the remainder were managed conservatively. The mean length of hospital stay was 12.41 +/- 4.54 days. The complications encountered included pseudocyst formation, ascites, hypocalcaemia, pleural effusion and coagulopathy.

CONCLUSIONS

The diagnosis of acute pancreatitis in children can be difficult. This is often due to ambiguous symptoms, signs and laboratory results. CT and ultrasound are essential investigations in the diagnosis and subsequent follow-up.

Impact of an asthma carepath on the management of acute asthma exacerbations

INTRODUCTION

Clinical pathways are being developed to standardise the management of acute asthma with the aim of improving asthma care. We evaluated the impact of an asthma carepath (CP), developed and instituted at a large community-based teaching hospital.

MATERIALS AND METHODS

Case records of consecutive asthma cases were reviewed after the implementation of a new asthma CP (November 1999 to March 2000). Data from July to October 1998 were used as historical control data [pre-carepath (pre-CP)]. Data collected included patient demographics, investigations performed, treatment prescribed, use of peak expiratory flow rate (PEFR) monitoring, length of stay (LOS) and asthma relapse rates.

RESULTS

One hundred and eighteen consecutive cases treated according to CP were compared with 67 pre-CP controls. There was no significant difference between the two groups with regard to LOS, use of PEFR monitoring, use of systemic steroids in hospital or asthma relapse after discharge (P > 0.05). A significant decrease in sputum tests (34.3% pre-CP versus 18.6% CP, P = 0.017) and use of antibiotics (62.7% pre-CP versus 30.4% CP, P < 0.001) was observed for patients on CP. The proportion of patients who had their salbutamol reviewed (49.3% pre-CP versus 73.7% CP, P = 0.001) and oxygen reviewed (25.8% pre-CP versus 73.8% CP, P = 0.004) was also significantly higher for cases on CP.

CONCLUSION

Although the asthma CP did not significantly reduce LOS or early relapse, it was associated with a significant reduction of the use of sputum tests and antibiotics. Review of salbutamol and oxygen as treatment was also more likely.

An audit of patients with rheumatic disease requiring medical intensive care

INTRODUCTION

Medical intensive care for patients with rheumatic disease is usually complicated by significant morbidity and mortality. The aims of this study were to examine the reasons for admission, the outcomes of these patients and the possible prognostic factors in an Asian cohort.

MATERIALS AND METHODS

This was a retrospective study of the case records of 29 admissions to the medical intensive care unit (MICU) of Tan Tock Seng Hospital (TTSH) from August 1999 to August 2000.

RESULTS

There were 28 patients admitted, of whom 1 had a repeat admission. The majority of these patients were young (mean age 38.9 +/- 16.3 years) and 71.4% were females. Twenty patients (71.4%) had systemic lupus erythematosus (SLE). The main reasons for admission were infection/sepsis syndrome (n = 18), hypotension (n = 16) and acute respiratory failure (n = 14). The observed in-hospital mortality was 64.3%, which was higher than the predicted risk of hospital death of 47.3%. Infection contributed to 55.6% of deaths. The patients who died had a longer mean duration of the rheumatic disease, higher APACHE II scores, higher rates of hypertension and hyperlipidaemia, higher doses of steroid and immunosuppressive therapy and more organ failures. Renal failure and acute respiratory distress syndrome were the two most common organ failures in patients who died.

CONCLUSION

Many of our critically-ill patients with rheumatic disease were young females with good functional status. Despite the high mortality, they should be aggressively treated because infection and acute respiratory failure are potentially reversible.

Copper and silver complexes containing organic azide ligands: syntheses, structures, and theoretical investigation of [HB(3,5-(CF3)2Pz)3]CuNNN(1-Ad) and [HB(3,5-(CF3)2Pz)3]AgN(1-Ad)NN (where Pz = pyrazolyl and 1-Ad = 1-adamantyl)

Treatment of [HB(3,5-(CF3)2Pz)3]Na(THF) with CF3SO3Cu followed by 1-azidoadamantane affords [HB(3,5-(CF3)2Pz)3]CuNNN(1-Ad) in 65% yield. The solid state structure shows that the copper atom is coordinated to the terminal nitrogen atom (NT) of the azidoadamantane ligand. The related silver(I) adduct can be prepared in 80% yield by the treatment of [HB(3,5-(CF3)2Pz)3]Ag(THF) with 1-azidoadamantane. However, [HB(3,5-(CF3)2Pz)3]AgN(1-Ad)NN shows a different bonding mode where the silver atom coordinates to the alkylated nitrogen atom (NA) of the azidoadamantane ligand. Asymmetric stretching bands of the azido group for copper and silver adducts appear at 2143 and 2120 cm-1, respectively. Theoretical investigation shows that steric effects do not play a dominant role in determining the bonding mode of the azide ligand in these two metal complexes. Although the copper(I) ion affinity for the two coordinating sites NT and NA is nearly identical, copper-azide back-bonding interactions favor the copper-NT mode of bonding over the copper-NA mode. Silver (a very poor back-bonding metal) prefers the NA site for coordination. The NA site has a significantly higher proton affinity and slightly higher sodium ion affinity. Important structural parameters for [HB(3,5-(CF3)2Pz)3]CuNNN(1-Ad) and [HB(3,5-(CF3)2Pz)3]AgN(1-Ad)NN are as follows: Cu-NT 1.861(3) A, NT-N 1.136(4) A, N-NA 1.219(4) A, NT-N-NA 173.1(3) degrees; Ag-NA 2.220(5) A, NT-N 1.143(12) A, N-NA 1.227(10) A, NT-N-NA 176.8(12) degrees. Overall, the azidoadamantane ligand does not undergo any significant changes upon coordination to Cu(I) or Ag(I) ions.

A case report of Aspergillus hypersensitivity syndrome with obstructing bronchial aspergillosis

INTRODUCTION

A 62-year-old Indian male with diabetes mellitus presented with atypical, overlap features of Aspergillus hypersensitivity syndrome and obstructing bronchial aspergillosis.

CLINICAL PICTURE

He was febrile and tachypnoeic with diffuse crepitations and wheezing. Chest X-ray was normal but eosinophil count was 2900/mm3 and Ig E > 10,000 IU/ml.

TREATMENT AND OUTCOME

He responded initially to high dose steroid therapy but deteriorated subsequently from extensive mucus plugging of the bronchial tree which resulted in respiratory failure and death. He was HIV-negative.

CONCLUSION

Culture and histologic examination of bronchoscopically identified tracheobronchial mucus plugs should be performed as early treatment may be life-saving.

Morbidity after a bite from a 'non-venomous' pet snake

We report the first recorded case of morbidity from the bite of a red-neck keelback snake (Rhabdophis subminiatus) from South East Asia. This is a species of the Colubrid family which originated from South East Asia. Severe envenomation from this snake was reported as poisonous in the West as far back as 1978 but it is still being classified as non-venomous. This classification led our patient to keep this 'harmless' snake as a pet. We recommend that this snake be reclassified as 'venomous' or at least warnings be issued to the public not to keep it as a pet.

A prospective study of infections with atypical pneumonia organisms in acute exacerbations of chronic bronchitis

The objective of this paper was to study the incidence of 6 atypical pneumonia pathogens or atypical organisms in local patients admitted for acute exacerbation of chronic bronchitis. This is a prospective observational study. Over a period of 3 years (1995 to 1997), 90 patients admitted to a large general hospital in Singapore for acute exacerbation of chronic bronchitis were tested for the following infections: Legionella, Mycoplasma, Chlamydia, influenza A, influenza B and parainfluenza viruses, using paired serological examination. The antibiotic prescribing pattern by the attending physicians in these cases were also examined. Positive serologies were found in 31 patients (34%), of whom 26 patients (28%) had viral infections. The most common organism was influenza A with 18 positive serologies (20%). Five patients were tested positive for Legionella. There was no evidence of acute infections by Mycoplasma pneumoniae or chlamydia using serological tests.

Impact on quality of patient care and procedure use in the medical intensive care unit (MICU) following reorganisation

We conducted this retrospective, cohort study to evaluate the quality of patient care and procedure use in the medical care unit (MICU) following reorganisation and staffing by an intensivist. Consecutive admissions to an adult MICU in a university affiliated hospital during two 3-month periods, August to October 1993 (Period 1, n = 112) and January to March 1994 (Period 2, n = 127) were analysed. In Period 1, the MICU was run under the open system in which patient care was provided by the individual attending physicians. In Period 2, a resident MICU team led by a trained intensivist took over the medical care from the primary physicians when the patients were admitted to the MICU. The intensivist also vetted MICU admission and decided on MICU discharge. In addition, there was a resident respiratory therapist to attend to ventilatory care during office hours. After office hours, the care of the MICU was delegated to the on-call team on a rotational basis among the medical departments. This was the semi-closed ICU model. The patients in the two periods were similar with respect to age, sex, race, source of admission and APACHE II scores. There was improvement in the median ICU length of stay for survivors from 3 days in Period 1, to 2 days in Period 2 (P = 0.0114). The relative risk of ICU death in Period 1 compared to Period 2 was 1.23 (P = 0.286). There was no significant difference in the use of peritoneal dialysis (5.4% versus 6.3%) and mechanical ventilation (55.4% versus 49.6%). However, utilisation of intra-arterial lines and pulmonary artery catheters increased from 0% in both Periods 1 and 2 to 23.6% and 5.5%, respectively. Reorganisation of the MICU in Period 2 resulted in reduced length of MICU stay for survivors. Hence, we believe that coverage by a dedicated ICU team and active respiratory care by a respiratory therapist during office hours were beneficial for the care of the critically ill. There was also a noticeable increase in the use of invasive monitoring.

Incorporating the effect of display formats in cognitive modelling

Cognitive modelling provides a method for identifying strategies used by people to acquire and process information. Previous research has shown that the way in which problem information is represented can have a profound effect on performance. The purpose of this study is to integrate the effects of display formats into cognitive modelling by determining the locus of that effect in information processing strategies. The research accomplished that goal by constructing cognitive models of information processing strategies using verbal protocols, and then relating those models to performance. In the process of constructing models, the study establishes a link between previous research in display formats and cognitive modelling techniques by determining how the models must be adjusted to account for the differences in performance related to a specific type of display format. The ability of cognitive modelling techniques to predict performance is discussed, and issues for further research to improve the utility of such models are presented.