[The association between Helicobacter pylori virulence factor genotypes and gastroduodenal diseases in children]

Objective: To investigate the association between Helicobacter pylori (Hp) virulence factor genotypes and the degree and activity of gastric mucosa pathological changes in pediatric gastroduodenal diseases. Methods: This retrospective cohort study was conducted from May 2020 to October 2020. The frozen strains of Hp, which were cultured with the gastric mucosa of 68 children with gastroscopy confirmed gastroduodenal diseases who visited the children's hospital of Zhejiang University School of Medicine from April 2012 to December 2014, were resuscitated. After extracting DNA from these Hp strains, PCR amplification and agarose gel electrophoresis were performed to determine the detection rate of cytotoxin-associated protein A (cagA),vacuolating cytotoxin A (vacA)(s1a、s1b/s2,m1/m2), outer inflammatory protein A (oipA),blood group antigen binding adhesin (babA),duodenal ulcer promoting protein A (dupA) genes; oipA genes were sequenced to determine the gene status. The patients were divided into different groups according to the findings of gastroscopy and gastric mucosa pathology. The detection rates of various virulence factor genotypes among different groups were compared using χ2 tests or Fisher's exact tests. Results: The 68 Hp strains all completed genetic testing. According to the diagnostic findings of gastroscopy, the 68 cases were divided into 47 cases of superficial gastritis and 21 cases of peptic ulcer. Regarding the pathological changes of gastric mucosa, 8 cases were mild, and 60 cases were moderate and severe according to the degree of inflammation; 61 cases were active and 7 cases inactive according to the activity of inflammation. The overall detection rates of cagA, vacA, vacA s1/m2, functional oipA, babA2, and dupA virulence factor genes were 100% (68/68), 100% (68/68), 94% (64/68), 99% (67/68), 82% (56/68), and 71% (48/68), respectively. In the superficial gastritis group, their detection rates were 100% (47/47), 100% (47/47), 96% (45/47), 98% (46/47), 81% (38/47), and 70% (33/47), respectively; in the peptic ulcer group, their detection rates were 100% (21/21), 100% (21/21), 90% (19/21), 100% (21/21), 86% (18/21), and 71% (15/21), respectively. There was no statistically significant difference between the two groups (all P>0.05). In the mild gastric mucosa inflammation group, the detection rates of the above six genotypes were 8/8, 8/8, 8/8, 7/8, 7/8, and 5/8, respectively; and in the moderate to severe inflammation groups, the detection rates were 100% (60/60), 100% (60/60), 93% (56/60), 100% (60/60), 82% (49/60), and 72% (43/60), respectively, with no statistically significant difference between the two groups (all P>0.05). In the active inflammation group, the detection rate of six genotypes were 100% (61/61), 100% (61/61), 93% (57/61), 98% (60/61), 82% (50/61), and 72% (44/61), respectively; and in the inactive inflammation group, they were 7/7, 7/7, 7/7, 7/7, 6/7, and 4/7, respectively. Again, there was no statistically significant difference between the two groups (all P>0.05). There was no statistically significant difference in the detection rate of combinations of 4 or 5 virulence factor genes among the different groups (all P>0.05). Conclusions: CagA, vacA, vacA s1/m2, functional oipA, babA2, and dupA genes are not associated with superficial gastritis and peptic ulcer in children, or with the degree and activity of gastric mucosa pathological inflammation. Different gene combinations of cagA, vacA, oipA, babA2, and dupA have no significant effects on predicting the clinical outcome of Hp infection in children.

[The relationship between genetic polymorphism of CYP2C19 and the efficacy of Helicobacter pylori eradication therapy in children]

Objective: To investigate the relationship between genetic polymorphisms of cytochrome P450 2C19 (CYP2C19) and the efficacy of Helicobacter pylori (Hp) eradication therapy in children. Methods: The retrospective cohort study was conducted on 125 children with gastroscopy and positive rapid urease test (RUT) from September 2016 to December 2018 who presented to the Children's Hospital of Zhejiang University School of Medicine due to gastrointestinal symptoms including nausea, vomiting, abdominal pain, bloating, acid reflux, heartburn, chest pain, vomiting blood and melena. Hp culture and drug susceptibility test were carried out with gastric antrum mucosa before treatment. All the patients completed 2 weeks of standardized Hp eradication therapy and had ¹³C urea breath test 1 month after that, which was used to evaluate the curative effect. The DNA of gastric mucosa after RUT was analyzed and CYP2C19 gene polymorphism was detected. Children were grouped according to metabolic type. Combined with the results of Hp culture and drug susceptibility, the relationship between CYP2C19 gene polymorphism and the efficacy of Hp eradicative treatment was analyzed in children. Chi square test was used for row and column variables, and Fisher exact test was used for comparison between groups. Results: One hundred and twenty five children were enrolled in the study, of whom 76 were males and 49 females. The genetic polymorphism of CYP2C19 in these children found poor metabolizer (PM) of 30.4% (38/125), intermediate metabolizer (IM) of 20.8% (26/125), normal metabolizer (NM) of 47.2% (59/125), rapid metabolizer (RM) of 1.6% (2/125), and ultrarapid metabolizer (UM) of 0. There were statistically significant in positive rate of Hp culture among these groups (χ²=124.00, P<0.001). In addition, the successful rates of Hp eradication in PM, IM, NM and RM genotypes were 84.2% (32/38), 53.8% (14/26), 67.8% (40/59), and 0, respectively, with significant differences (χ²=11.35, P=0.010); those in IM genotype was significantly lower than that in PM genotype (P=0.011). With the same standard triple Hp eradicative regimen, the successful rate of Hp eradication for IM type was 8/19, which was lower than that of PM (80.0%, 24/30) and NM type (77.3%, 34/44) (P=0.007 and 0.007, respectively). There was a significant difference in the efficacy of Hp eradication treatment among different genotypes (χ²=9.72, P=0.008). According to the clarithromycin susceptibility result, the successful rate of Hp eradication treatment for IM genotype was 4/15 in the sensitive group and 4/4 in the drug-resistant group (χ²=6.97, P=0.018). Conclusions: The genetic polymorphism of CYP2C19 in children is closely related to the efficacy of Hp eradication treatment. PM has a higher successful rate of eradication treatment than the other genotypes.

Quantum oscillations in field-induced correlated insulators of a moiré superlattice

We report an observation of quantum oscillations (QOs) in the correlated insulators with valley anisotropy of twisted double bilayer graphene (TDBG). The anomalous QOs are best captured in the magneto resistivity oscillations of the insulators at v = -2, with a period of 1/B and an oscillation amplitude as high as 150 kΩ. The QOs can survive up to ∼10 K, and above 12 K, the insulating behaviors are dominant. The QOs of the insulator are strongly D dependent: the carrier density extracted from the 1/B periodicity decreases almost linearly with D from -0.7 to -1.1 V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1 m_e at D = ∼ -1.0 V/nm. Similar observations of QOs are also found at v = 2, as well as in other devices without graphite gate. We interpret the D sensitive QOs of the correlated insulators in the picture of band inversion. By reconstructing an inverted band model with the measured effective mass and Fermi surface, the density of state at the gap, calculated from thermal broadened Landau levels, agrees qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous QOs in this moiré system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.

AB1426 PREDICTORS OF RHEUMATIC TOXICITIES OF IMMUNE CHECKPOINT INHIBITORS AND CANCER OUTCOMES IN PATIENTS WITH ADVANCED MELANOMA

Background

Immune checkpoint inhibitors (ICIs) including monoclonal antibodies to PD-1 and CTLA-4 have activity across various cancers. Dedicated cohort studies have examined the epidemiology and clinical course of rheumatic toxicities (1–3) and the effect of pre-existing autoimmune disease has been explored (4), with limited assessment of the effect of non-immune mediated rheumatic disease (3). A positive association between ICI-induced rheumatic disease and favourable cancer outcomes has been suggested (1,2), although derived from heterogenous cancer populations.

Objectives

To identify risk factors for the development of ICI-induced rheumatic disease and predictors of cancer outcomes in patients with advanced melanoma.

Methods

A single-centre observational study of patients with stage III or IV melanoma receiving all available ICI therapies, who completed a for-purpose questionnaire to capture rheumatic symptoms and risk factors upon recruitment and at 12-months. Symptom severity was assessed according to patient reported measures such as visual analogue scale (VAS) scores for pain. Clinical details were extracted from patients’ medical records. Predictors of rheumatic toxicities and cancer outcomes were identified through regression analysis.

Results

Amongst 147 eligible patients, the prevalence of new or worsening rheumatic symptoms was 32.5% at recruitment and 21% at 12 months. The incidence of documented arthralgia, inflammatory arthritis and PMR-like syndrome was 39.5%, 5.4% and 3.4% respectively. Binary logistic regression identified pre-existing symptomatic rheumatic disease, including non-immune mediated rheumatic disease, as the primary risk factor for developing rheumatic toxicities (OR 3.161). Continuation of ICI therapy (OR 16.52), followed by rheumatic toxicities (OR = 4.368) were predictors of favourable tumour response.

Conclusion

Rheumatic toxicities of ICI therapy commonly affect patients with melanoma and are more likely to occur in patients with pre-existing autoimmune and non-immune mediated rheumatic disease. Continuation of ICI therapy improves cancer outcomes and can be facilitated by early detection of rheumatic symptoms using patient reported outcome measures.

Table 1.

Bivariate logistic regression of predictors of patient-reported rheumatic toxicity. Sig., Significance; OR, Odds ratio; CI, confidence interval; BRAF/MEK, BRAF and MEK inhibitors; PD-1, Programmed Cell Death protein – 1; CTLA-4, Cytotoxic T-lymphocyte-associated protein.

Figure 1.

A) Receiver-operator curve for accuracy of binary logistic regression model clinician-recorded rheumatic disease. (B) Area under receiver-operator curve. Test result variable(s): predicted probability. AUROC, Area Under Receiver-Operator Curve; Std. Error, Standard Error; Sig., Significance.

(a) Under the nonparametric assumption

(b) Null hypothesis: true area = 0.5

References

[1]Kostine M, Rouxel L, Barnetche T, Veillon R, Martin F, Dutriaux C, et al. Rheumatic disorders associated with immune checkpoint inhibitors in patients with cancer-clinical aspects and relationship with tumour response: a single-centre prospective cohort study. Ann Rheum Dis. 2018;77(3):393–8.

[2]Braaten TJ, Brahmer JR, Forde PM, Le D, Lipson EJ, Naidoo J, et al. Immune checkpoint inhibitor-induced inflammatory arthritis persists after immunotherapy cessation. Ann Rheum Dis. 2019;332–8.

[3]Buder-Bakhaya K, Benesova K, Schulz C, Anwar H, Dimitrakopoulou-Strauss A, Weber TF, et al. Characterization of arthralgia induced by PD-1 antibody treatment in patients with metastasized cutaneous malignancies. Cancer Immunol Immunother. 2018;67(2):175–82.

[4]Menzies AM, Johnson DB, Ramanujam S, Atkinson VG, Wong ANM, Park JJ, et al. Anti-PD-1 therapy in patients with advanced melanoma and preexisting autoimmune disorders or major toxicity with ipilimumab. Ann Oncol. 2017;28(2):368–76.

Disclosure of Interests

Alana Bruce: None declared, Alexander Menzies Consultant of: A.M.M. has participated in advisory boards for BMS, MSD, Novartis, Roche, Pierre-Fabre, Georgina Long Consultant of: GVL is consultant advisor for Aduro Biotech Inc, Agenus Inc, Amgen Inc, Array Biopharma inc, Boehringer Ingelheim International GmbH, Bristol-Myers Squibb, Evaxion Biotech A/S, Hexel AG, Highlight Therapeutics S.L., Merck Sharpe & Dohme, Novartis Pharma AG, OncoSec, Pierre Fabre, QBiotics Group Limited, Regeneron Pharmaceuticals Inc, Specialised Therapeutics Australia Pty Ltd., Brian Fernandes: None declared, Fredrick Joshua Consultant of: F.J. has performed clinical trials and participated in advisory boards for Abbvie, Pfizer, Novartis, Sanofi, Eli Lily and Roche

Persistence of Magnetism in Atomically Thin MnPS3 Crystals

The magnetic state of atomically thin semiconducting layered antiferromagnets such as CrI₃ and CrCl₃ can be probed by forming tunnel barriers and measuring their resistance as a function of magnetic field (H) and temperature (T). This is possible because the spins within each individual layer are ferromagnetically aligned and the tunneling magnetoresistance depends on the relative orientation of the magnetization in adjacent layers. The situation is different for systems that are antiferromagnetic within the layers in which case it is unclear whether magnetoresistance measurements can provide information about the magnetic state. Here, we address this issue by investigating tunnel transport through atomically thin crystals of MnPS₃, a van der Waals semiconductor that in the bulk exhibits easy-axis antiferromagnetic order within the layers. For thick multilayers below T ∼ 78 K, a T-dependent magnetoresistance sets in at μ₀H ∼ 5 T and is found to track the boundary between the antiferromagnetic and the spin-flop phases known from bulk measurements. We show that the magnetoresistance persists as thickness is reduced with nearly unchanged characteristic temperature and magnetic field scales, albeit with a different dependence on H, indicating the persistence of magnetism in the ultimate limit of individual monolayers.

Determining Interaction Enhanced Valley Susceptibility in Spin-Valley-Locked MoS2

Two-dimensional transition metal dichalcogenides (TMDCs) are recently emerged electronic systems with various novel properties, such as spin-valley locking, circular dichroism, valley Hall effect, and superconductivity. The reduced dimensionality and large effective masses further produce unconventional many-body interaction effects. Here we reveal strong interaction effects in the conduction band of MoS₂ by transport experiment. We study the massive Dirac electron Landau levels (LL) in high-quality MoS₂ samples with field-effect mobilities of 24 000 cm²/(V·s) at 1.2 K. We identify the valley-resolved LLs and low-lying polarized LLs using the Lifshitz-Kosevitch formula. By further tracing the LL crossings in the Landau fan diagram, we unambiguously determine the density-dependent valley susceptibility and the interaction enhanced g-factor from 12.7 to 23.6. Near integer ratios of Zeeman-to-cyclotron energies, we discover LL anticrossings due to the formation of quantum Hall Ising ferromagnets, the valley polarizations of which appear to be reversible by tuning the density or an in-plane magnetic field. Our results provide evidence for many-body interaction effects in the conduction band of MoS₂ and establish a fertile ground for exploring strongly correlated phenomena of massive Dirac electrons.

Intrinsic valley Hall transport in atomically thin MoS2

Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS₂, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS₂. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics.

Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom. Here, the authors observe room-temperature valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS₂ by purely electronic means, whereas no valley signal is detected for centrosymmetric bilayer MoS₂.

Twin Defect Derived Growth of Atomically Thin MoS2 Dendrites

Morphology management for tailoring the properties of monolayer transition-metal dichalcogenides (TMDCs), that is, molybdenum disulfide (MoS₂), has attracted great interest for promising applications such as in electrocatalysis and optoelectronics. Nevertheless, little progress has been made in engineering the shape of MoS₂. Herein, we introduce a modified chemical vapor deposition method to grow monolayer MoS₂ dendrites by pretreating substrates with adhesive tapes. The as-grown MoS₂ crystals are featured with hexagonal backbones with fractal shapes and tunable degrees. By characterizing the atomic structure, it is found that these morphologies are mainly initiated from the twin defect derived growth and controlled by the S:Mo vapor ratio. Due to the accumulated sulfur vacancies in the cyclic twin regions, strong enhancement of photoluminescence emission is localized, which determines the shape dependency of optical property. This work not only enriches the understanding of the twin defects derived crystal growth mechanism and extends its applications from nanomaterials to two-dimensional crystals, but also offers a robust and controllable protocol for shape-engineered monolayer TMDCs in electrochemical and optoelectronic applications.

Gate-tunable strong-weak localization transition in few-layer black phosphorus

Atomically-thin black phosphorus (BP) field-effect transistors show strong-weak localization transition, which is tunable through gate voltages. Hopping transports through charge impurity-induced localized states are observed at low carrier density regime. Variable-range hopping model is applied to simulate scattering behaviors of charge carriers. In the high carrier concentration regime, a negative magnetoresistance indicates weak localization effects. The extracted phase coherence length is power-law temperature-dependent [Formula: see text] and demonstrates inelastic electron-electron interactions and the 2D transport features in few-layer BP field-effect devices. The competition between localization and phase coherence lengths is investigated and analyzed based on observed gate-tunable strong-weak localization transition in few-layer BP.

Observation of A Raman mode splitting in few layer black phosphorus encapsulated with hexagonal boron nitride

We investigate the impact of encapsulation with hexagonal boron nitride (h-BN) on the Raman spectrum of few layer black phosphorus. The encapsulation results in a significant reduction of the line width of the Raman modes of black phosphorus, due to a reduced phonon scattering rate. We observe a so far elusive peak in the Raman spectra ∼4 cm^-1 above the A mode in trilayer and thicker flakes, which had not been observed experimentally. The newly observed mode originates from the strong black phosphorus inter-layer interaction, which induces a hardening of the surface atom vibration with respect to the corresponding modes of the inner layers. The observation of this mode suggests a significant impact of h-BN encapsulation on the properties of black phosphorus and can serve as an indicator of the quality of its surface.

Isolation and Characterization of Few-Layer Manganese Thiophosphite

This work reports an experimental study on an antiferromagnetic honeycomb lattice of MnPS₃ that couples the valley degree of freedom to a macroscopic antiferromagnetic order. The crystal structure of MnPS₃ is identified by high-resolution scanning transmission electron microscopy. Layer-dependent angle-resolved polarized Raman fingerprints of the MnPS₃ crystal are obtained, and the Raman peak at 383 cm^-1 exhibits 100% polarity. Temperature dependences of anisotropic magnetic susceptibility of the MnPS₃ crystal are measured in a superconducting quantum interference device. Anisotropic behaviors of the magnetic moment are explored on the basis of the mean field approximation model. Ambipolar electronic conducting channels in MnPS₃ are realized by the liquid gating technique. The conducting channel of MnPS₃ offers a platform for exploring the spin/valleytronics and magnetic orders in 2D limitation.

Odd-Integer Quantum Hall States and Giant Spin Susceptibility in p-Type Few-Layer WSe_{2}

We fabricate high-mobility p-type few-layer WSe_{2} field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe_{2}, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe_{2} offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus

We demonstrate that a field-effect transistor (FET) made of few-layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum exhibits a room-temperature hole mobility of 5200 cm²/(Vs), being limited just by the phonon scattering. At cryogenic temperatures, the FET mobility increases up to 45 000 cm²/(Vs), which is five times higher compared to the mobility obtained in earlier reports. The unprecedentedly clean h-BN-BP-h-BN heterostructure exhibits Shubnikov-de Haas oscillations and a quantum Hall effect with Landau level (LL) filling factors down to v = 2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass of m^* = 0.26 m₀ is measured, and a Landé g-factor of g = 2.47 is reported. Furthermore, an indication for a distinct hole transport behavior with up- and down-spin orientations is found.

Even-odd layer-dependent magnetotransport of high-mobility Q-valley electrons in transition metal disulfides

In few-layer transition metal dichalcogenides (TMDCs), the conduction bands along the ΓK directions shift downward energetically in the presence of interlayer interactions, forming six Q valleys related by threefold rotational symmetry and time reversal symmetry. In even layers, the extra inversion symmetry requires all states to be Kramers degenerate; whereas in odd layers, the intrinsic inversion asymmetry dictates the Q valleys to be spin-valley coupled. Here we report the transport characterization of prominent Shubnikov-de Hass (SdH) oscillations and the observation of the onset of quantum Hall plateaus for the Q-valley electrons in few-layer TMDCs. Universally in the SdH oscillations, we observe a valley Zeeman effect in all odd-layer TMDC devices and a spin Zeeman effect in all even-layer TMDC devices, which provide a crucial information for understanding the unique properties of multi-valley band structures of few-layer TMDCs.

Few-layer transition metal dichalcogenides exhibit strong spin-valley entanglement and unconventional quantum Hall states, however their study has been limited by electron mobility. Here, the authors explore how quantum transport varies between even- and odd-layered systems of high mobility.

A fast transfer-free synthesis of high-quality monolayer graphene on insulating substrates by a simple rapid thermal treatment

The transfer-free synthesis of high-quality, large-area graphene on a given dielectric substrate, which is highly desirable for device applications, remains a significant challenge. In this paper, we report on a simple rapid thermal treatment (RTT) method for the fast and direct growth of high-quality, large-scale monolayer graphene on a SiO2/Si substrate from solid carbon sources. The stack structure of a solid carbon layer/copper film/SiO2 is adopted in the RTT process. The inserted copper film does not only act as an active catalyst for the carbon precursor but also serves as a "filter" that prevents premature carbon dissolution, and thus, contributes to graphene growth on SiO2/Si. The produced graphene exhibits a high carrier mobility of up to 3000 cm(2) V(-1) s(-1) at room temperature and standard half-integer quantum oscillations. Our work provides a promising simple transfer-free approach using solid carbon sources to obtain high-quality graphene for practical applications.

Paediatric CT dose: a multicentre audit of subspecialty practice in Australia and New Zealand

OBJECTIVES

To evaluate paediatric CT dosimetry in Australia and New Zealand and calculate size-specific dose estimates (SSDEs) for chest and abdominal examinations.

METHODS

Eight hospitals provided data from 12 CT systems for 1462 CTs in children aged 0-15. Imaging data were recorded for eight examinations: head (trauma, shunt), temporal bone, paranasal sinuses, chest (mass) and chest HRCT (high-resolution CT), and abdomen/pelvis (mass/inflammation). Dose data for cranial examinations were categorised by age and SSDEs by lateral dimension. Diagnostic reference ranges (DRRs) were defined by the 25th and 75th percentiles. Centralised image quality assessment was not undertaken.

RESULTS

DRRs for 201 abdominopelvic SSDEs were: 2.8-4.7, 3.6-11.5, 8.5-15.0, 7.6-15, and 10.6-16.2 for the <15 cm, 15-19 cm, 20-24 cm, 25-29 cm and >30 cm groups, respectively. For 147 chest examinations using these body width categories, SSDE DRRs were 2.0-4.4, 3.3-7.9, 4.0-9.4, 4.5-12, and 6.5-12. Kilovoltage peak (kVp), but not AEC or IR, was associated with SSDE (parameter estimate [standard error]: 0.12 (0.03); p < 0.0001).

CONCLUSIONS

Australian and New Zealand paediatric CT DRRs and abdominal SSDEs are comparable to international data. SSDEs for chest examinations are proposed. Dose variations could be reduced by adjusting kVp.

KEY POINTS

• SSDEs can be calculated for all patients, CT systems, and practices • Kilovoltage peak (kVp) has the greatest association with dose in similar-sized patients • Paediatric DRRs for CT are now available for use internationally.

van der Waals epitaxial growth of atomically thin Bi₂Se₃ and thickness-dependent topological phase transition

Two-dimensional (2D) atomic-layered heterostructures stacked by van der Waals interactions recently introduced new research fields, which revealed novel phenomena and provided promising applications for electronic, optical, and optoelectronic devices. In this study, we report the van der Waals epitaxial growth of high-quality atomically thin Bi2Se3 on single crystalline hexagonal boron nitride (h-BN) by chemical vapor deposition. Although the in-plane lattice mismatch between Bi2Se3 and h-BN is approximately 65%, our transmission electron microscopy analysis revealed that Bi2Se3 single crystals epitaxially grew on h-BN with two commensurate states; that is, the (1̅21̅0) plane of Bi2Se3 was preferably parallel to the (1̅100) or (1̅21̅0) plane of h-BN. In the case of the Bi2Se3 (2̅110) ∥ h-BN (11̅00) state, the Moiré pattern wavelength in the Bi2Se3/h-BN superlattice can reach 5.47 nm. These naturally formed thin crystals facilitated the direct assembly of h-BN/Bi2Se3/h-BN sandwiched heterostructures without introducing any impurity at the interfaces for electronic property characterization. Our quantum capacitance (QC) measurements showed a compelling phenomenon of thickness-dependent topological phase transition, which was attributed to the coupling effects of two surface states from Dirac Fermions at/or above six quintuple layers (QLs) to gapped Dirac Fermions below six QLs. Moreover, in ultrathin Bi2Se3 (e.g., 3 QLs), we observed the midgap states induced by intrinsic defects at cryogenic temperatures. Our results demonstrated that QC measurements based on h-BN/Bi2Se3/h-BN sandwiched structures provided rich information regarding the density of states of Bi2Se3, such as quantum well states and Landau quantization. Our approach in fabricating h-BN/Bi2Se3/h-BN sandwiched device structures through the combination of bottom-up growth and top-down dry transferring techniques can be extended to other two-dimensional layered heterostructures.

Intermediate metallic phase in VO₂ observed with scanning tunneling spectroscopy

This investigation focuses on the formation of nanoscale puddles of an intermediate metallic phase (IMP) in the metal-insulator transition (MIT) temperature regime of single-crystalline vanadium dioxide (VO2) nanowires. The electronic structure of VO2 nanowires was examined with scanning tunneling spectroscopy. The evolution of the local density of states of individual nanowires throughout the MIT regime is presented with differential tunneling conductance spectra and images measured as the temperature was increased. Our results show that the formation of an IMP plays an important role in the MIT of intrinsic VO2.

Wearing a crotch strap on a correctly fitted lifejacket improves lifejacket performance

Wearing a lifejacket when immersed in water should support the wearer, maintaining their airway clear of the water. It is proposed that a retention system would improve airway protection by improving retention of the lifejacket around the torso. Study one (n = 10) quantified the performance of lifejackets immediately following a step into water from height when a lifejacket was worn with a crotch strap (two different tightness) and without a crotch strap. Airway freeboard was improved when wearing a crotch strap (P < 0.05) compared with no crotch strap. Study two used a manikin to examine the performance of lifejackets with and without a crotch strap during 3-h exposures to waves. During exposure to waves, the time taken to aspirate the lethal dose of seawater for drowning was doubled when wearing a crotch strap compared with the no-crotch-strap conditions (P < 0.001). Therefore, wearing a crotch strap (functioning retention system) on a correctly fitted lifejacket improves airway protection following accidental immersion and prolonged wave exposure.

Histological and finite element analysis of cell death due to irreversible electroporation

Irreversible electroporation (IRE) has been shown to be an effective method of killing cells locally. In contrast to radiofrequency ablation, the mechanism by which cells are thought to die via IRE is the creation of pores in cell membranes, without substantial increase in tissue temperature. To determine the degree to which cell death is non-thermal, we evaluated IRE in porcine hepatocytes in vivo. Using pulse widths of 10μs, bursts of 3 kV square-wave pulses were applied through a custom probe to the liver of an anesthetized pig. Affected tissue was evaluated histologically via stainings of hematoxylin & eosin (H&E), nitroblue tetrazolium (NBT) to monitor cell respiration and TUNEL to gauge apoptosis. Temperature was measured during the application of electroporation, and heat transfer was modeled via finite element analysis. Cell death was calculated via Arrhenius kinetics. Four distinct zones were observed within the ring return electrode; heat-fixed tissue, coagulation, necrotic, and viable. The Arrhenius damage integral estimated complete cell death only in the first zone, where the temperature exceeded 70°C, and partial or no cell death in the other zones, where maximum temperature was approximately 45°C. Except for a limited area near the electrode tip, cell death in IRE is predominantly due to a non-thermal mechanism.

Anisotropic paramagnetism of monoclinic Nd2Ti2O7 single crystals

The anisotropic paramagnetism and specific heat in Nd(2)Ti(2)O(7) single crystals are investigated. The angular dependence of the magnetization and Weiss temperatures show the dominant role of the crystal field effect in the magnetization. By incorporating the results from the diluted samples, contributions to the Weiss temperature from exchange interactions and crystal field interactions are isolated. The exchange interactions are found to be ferromagnetic, while the crystal field contributes a large negative part to the Weiss temperature, along all three crystallographic directions. The specific heat under a magnetic field reveals a two-level Schottky ground state scheme, due to the Zeeman splitting of the ground state doublet, and the g-factors are thus determined. These observations provide solid foundations for further investigations of Nd(2)Ti(2)O(7).

CathCam guide wire-directed colonoscopy: first pilot study in patients with a previous incomplete colonoscopy

BACKGROUND AND STUDY AIMS

Conventional colonoscopy as the gold standard for large-bowel diagnostics and therapy may fail in 5 %-20 % of cases, depending on the experience of the examiner. Colonoscopy is regarded as difficult and painful by many patients. In an attempt to overcome the limitations of conventional colonoscopes, a guide wire-directed, thin, flexible diagnostic colonoscope, the CathCam was developed. In this prospective pilot study, we report its use in patients in whom conventional colonoscopy had failed.

PATIENTS AND METHODS

49 patients with a previous or current failure of complete colonoscopy were invited to participate in a trial using the new CathCam system, and 14 (nine men; mean age 59 years) accepted. The CathCam is an 11-mm diameter disposable, multilumen catheter, with visualization by a 3-mm camera with six light-emitting diodes. In the first five patients, the CathCam was inserted over a newly developed 0.024-inch, hinged, lumen-seeking guide wire. Subsequently, a modified combined approach was used: a conventional colonoscope was introduced into the sigmoid or left colon, then the guide wire was advanced as far as possible, followed by CathCam insertion over it. Caecal intubation rate, insertion times and patient discomfort were recorded; patients received low-dose midazolam sedation (2-5 mg).

RESULTS

One patient was excluded during colonoscopy. The caecum could be eventually reached in 12 of 13 patients; in the remaining patient a significant sigmoid stricture could be passed, but further advancement appeared too risky. The mean caecal intubation time was 24 minutes (range 3-105 min). Only two patients experienced pain and discomfort during the procedure (one immediate assessment and one case reported at later telephone interview). No complications occurred, and previously undiagnosed important findings were obtained in 9 cases.

CONCLUSIONS

A combined approach, consisting of guide wire insertion via a partially introduced colonoscope followed by CathCam or colonoscope insertion into the caecum was successful in over 90 % of patients with previous failure of complete colonoscopy. Further improvements may make this system suitable for use as a standard diagnostic colonoscope, either as a single unit (CathCam plus guide wire) or using the guide wire alone with a standard colonoscope in difficult cases.

Right internal carotid pseudoaneurysm mimicking a retropharyngeal abscess in a child

A 7-year-old girl with tonsillar infection with antibiotics. Two weeks later, there was a right sided neck lump. Computed tomography scans demonstrated a predominantly hypodense right retropharyngeal area with peripheral enhancement and mass effect. There was intense enhancement within the postero-superior aspect of the lesion which was continuous with the right internal carotid artery. Ultrasound demonstrated tapering of the right internal carotid artery. Magnetic resonance imaging and magnetic resonance arteriography showed a right internal carotid artery pseudoaneurysm. Surgical exploration confirmed the finding. This case highlights an unusual presentation of an internal carotid pseudoaneurysm and how imaging provided the diagnosis.

Temperature trends in total hip arthroplasty: a retrospective study

The purpose of this study was to define the temporal trend in body temperature of patients during the first 5 days after total hip arthroplasty (THA). The medical records of 98 consecutive THAs were reviewed, 88 clinically uncomplicated cases were included. The average maximum temperature reached during the study period was 38.08 degrees C, a 3.7% (P< or =.01) increase from the preoperative base line of 36.64 degrees C. In this study, 62.5% of patients reached a temperature > or =38.0 degrees C; 19.3% > or = 38.5 degrees C; and 3.4% > or = 39.0 degrees C. No patients had a preoperative temperature of > or =38 degrees C recorded. On the first postoperative day, 39 patients had a temperature > or =38 degrees C. The number of febrile patients progressively decreased until by the fifth postoperative day, only 5 patients had a temperature > or =38 degrees C recorded.

Chloroform: exposure estimation, hazard characterization, and exposure-response analysis

Chloroform has been assessed as a Priority Substance under the Canadian Environmental Protection Act. The general population in Canada is exposed to chloroform principally through inhalation of indoor air, particularly during showering, and through ingestion of tap water. Data on concentrations of chloroform in various media were sufficient to serve as the basis for development of deterministic and probabilistic estimates of exposure for the general population in Canada. On the basis of data acquired principally in studies in experimental animals, chloroform causes hepatic and renal tumors in mice and renal tumors in rats. The weight of evidence indicates that chloroform is likely carcinogenic only at concentrations that induce the obligatory precursor lesions of cytotoxicity and proliferative regenerative response. Since this cytotoxicity is primarily related to rates of formation of reactive, oxidative metabolites, dose response has been characterized in the context of rates of formation of reactive metabolites in the target tissue. Results presented here are from a "hybrid" physiologically based pharmacokinetic (PBPK) animal model that was revised to permit its extension to humans. The relevant measure of exposure response, namely, the mean rate of metabolism in humans associated with a 5% increase in tumor risk (TC05), was estimated on the basis of this PBPK model and compared with tissue dose measures resulting from 24-h multimedia exposure scenarios for Canadians based on midpoint and 95th percentiles for concentrations in outdoor air, indoor air, air in the shower compartment, air in the bathroom after showering, tap water, and food. Nonneoplastic effects observed most consistently at lowest concentrations or doses following repeated exposures of rats and mice to chloroform are cytotoxicity and regenerative proliferation. As for cancer, target organs are the liver and kidney. In addition, chloroform has induced nasal lesions in rats and mice exposed by both inhalation and ingestion at lowest concentrations or doses. The mean rate of metabolism associated with a 5% increase in fatty cysts estimated on the basis of the PBPK model was compared with tissue dose measures resulting from the scenarios already described, and lowest concentrations reported to induce cellular proliferation in the nasal cavities of rats and mice were compared directly with midpoint and 95th percentile estimates of concentrations of chloroform in indoor air in Canada. The degree of confidence in the underlying database and uncertainties in estimates of exposure and in characterization of hazard and dose response are delineated.