Magnetic phase transition from paramagnetic in Nb2AlC-MAX to superconductivity-like diamagnetic in Nb2C-MXene: an experimental and computational analysis

Transition metal carbides (TMCs) have recently emerged as competent members among the family of two-dimensional (2D) materials, owing to their promising applications. There are many promising applications of MXenes; however, their magnetic properties lack a wide margin, both experimentally as well as theoretically, which needs to be investigated for potential use in spintronics. In this study, we carried out a comprehensive etching process via selective extraction of Al layers from Nb₂AlC-MAX using a wet electrochemical route under well-optimized conditions to obtain fine 2D-Nb₂C MXene sheets. Structural analysis using X-ray diffraction (XRD) confirms the effective removal of Al followed by confirmation of a 2D layered structure from morphological analysis using scanning electron microscopy (SEM). Zero-field-cooled (ZFC) and field-cooled (FC) measurements of MAX and MXene at different field strengths were performed using a superconducting quantum interference device (SQUID). Magnetic measurements reveal the paramagnetic nature of Nb₂AlC-MAX measured under 5 mT; however, this changes to a clear superconductor-like diamagnetic behavior with a shift of the magnetization from positive to negative values at low temperatures when measured under 5 mT and 10 mT for Nb₂C MXene. The diamagnetism, however, is changed to paramagnetism at 100 mT, which shows the existence of critical fields known typically for a type-II superconductor. To gain an insight into this unusual behavior in MXene, density functional theory (DFT) first-principles calculation was also performed in Wein2K software using spin-polarized generalized gradient approximation (sp-GGA). The magnetic moment of the compound is calculated to be negative, which corresponds well with the experimental finding and suggests that the negative magnetic moment originated from the d-orbital of Nb₂C. The present report provides a pathway to deeply understanding the existence of superconductivity-like diamagnetic behavior in Nb₂C MXene, which is useful for future magnetic applications.

Transition metal carbides (TMCs) have recently emerged as competent members among the family of two-dimensional (2D) materials, owing to their promising applications.

In two-dimensional (2D) materials, magnetism at the nanoscale is at the forefront of many cutting-edge technological applications, such as spintronic devices. Naguib et al. have synthesized a new class of two-dimensional materials, known as MXenes (M_nX_n+1), discovered in 2011, giving a possibility of magnetism in such 2D materials and their promising uses in spintronic devices.¹ These 2D layer structured early transition metal carbides and/or nitrides are known as MXenes, so named to indicate their structural similarities with graphene.² MXenes are derived from 3D MAX phases (space group P6₃/mmc) in which “M” is an early transition metal, e.g., Ti, Ta, V, etc.; “A” is mainly a group 13 or group 14 element (group III-A or IV-A), e.g., Si, Al; “X” is a carbide, nitride or can be both; and n = 1, 2, 3 represents the number of layers, forming 211, 312 and 413 phases.^3–5 Over the past decade, this new material has gained enormous attention, thus developing an entirely new research field to disclose the properties of the 2D state of this material. The materials in the 2D regime own a cluster of astonishing physical properties as compared to the 3D nature, but intrinsic two-dimensional magnetism has proved to be challenging. As 2D semiconductors have revamped the field of electronics, similarly, magnetism in 2D materials could remodel spintronic devices that can employ a spin degree of freedom.^6,7Nb₂C MXene was first synthesized by Naguib et al., but they just reported its electrochemical activity as a promising electrode material.⁴ Further work has been reported in Nb₂C with various biomedical applications, energy storage, supercapacitors, and nanoelectronics.^9–19 As far as the magnetism in such 2D MXenes is concerned, it remains less investigated, and this research void needs to be filled. Recently, Babar et al. reported the observation of superconductivity in as-prepared powdered Nb₂C for the first time, with the highest onset transition temperature T_c,onset = 12.5 K among the MXene family. However, the authors did not discuss the magnetic nature of the parent Nb₂AlC MAX itself and did not reason for the presence of unusual magnetic effects in MXene.⁸ MXenes are favorable members of 2D magnetism, and different magnetic natures are computationally predicted in various carbide and nitride MXenes.^7,20 The existence of novel room-temperature ferromagnetic order in doped MXene and the coexistence of different magnetic phases in MXene, along with experimental evidence, indicate its potential of hosting diverse magnetic natures.^21,22 Considerable research has been focused on these 2D structures due to their importance and favorable applications, such as spintronics. MXene could provide a vast platform for exploring the magnetic properties and is one of the best candidates that can host superconductivity as compared to other members of the 2D family. Experimental studies are generally dependent upon numerous variables, thus affecting the research pace. However, density functional theory-based first principles calculation and theoretical simulations are a successful way to examine and foresee the properties of low-dimensional materials. This provoked us to theoretically explore superconductivity in Nb₂C and their validation through superconductivity measurements of experimentally synthesized Nb₂C MXene. In this work, we report a systematic etching mechanism of Nb₂C MXene to obtain fine 2D sheets via a chemical etching route using hydrofluoric (HF) acid. Structural and morphological studies using the X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and elemental analysis by energy-dispersive X-ray spectroscopy (EDX) show the effective removal of Al from the parent 3D-Nb₂AlC MAX, thus revealing an accordion-like sheet structure. Optical analysis indicates a significant reduction in bandgap after chemical etching. Magnetic properties were carried out to observe the signatures of superconductivity (a perfect diamagnetic state, negative magnetic moment) and its magnetic nature at room temperature. To study the magnetic nature of as-prepared powder-form Nb₂C, density functional theory (DFT) first principles calculation was carried out through Wein2K using spin-polarized generalized gradient approximation (sp-GGA). The magnetic moment of the compound is calculated to be −0.00485, which although but small is important, as the value is negative, which is an indication of the presence of diamagnetism in Nb₂C. Here, the detailed chemical etching process, magnetic properties of Nb₂AlC MAX and its effect on magnetic phase of Nb₂C MXene, and the density functional theory calculation are reported, which were not discussed by Babar et al. in ref. 8.     

Fitness costs in chlorfenapyr-resistant populations of the chive maggot,Bradysia odoriphaga

The chive maggot, Bradysia odoriphaga (Yang and Zhang) is an economically important insect pest, affecting many key vegetables, including Chinese chive, especially in northern China. Chlorfenapyr, a halogenated pyrrole insecticide that interferes with mitochondrial oxidative phosphorylation is widely used against B. odoriphaga. In this study, we evaluated selection-induced resistance to chlorfenapyr and fitness costs in B. odoriphaga. The results showed that B. odoriphaga developed 43.32-fold resistance after continuous exposure to chlorfenapyr for over 10 consecutive generations. The life-history traits of chlorfenapyr-resistant and susceptible strains were compared using age-stage, two-sex life table approach. No significant effects were observed on the longevity and pre-adult period. However, reduction in the total pre-oviposition period (TPOP) and fecundity (eggs/female) were observed in the resistant strain. Moreover, the demographic parameters such as intrinsic rate of increase (r), net reproductive rate (R0) and finite rate of increase (λ) were also decreased significantly in the resistant strain compared to the susceptible strain. These results showed the potential of B. odoriphaga to develop resistance against chlorfenapyr under continuous selection pressure. Furthermore, there was a fitness cost linked with chlorfenapyr resistance in B. odoriphaga. We conclude that a better knowlegde on the trade-off at play between resistance degree and fitness cost could be crucial for developing further management of B. odoriphaga in China.     

Paratracheal air cysts: prevalence and relevance to pulmonary emphysema and bronchiectasis using thoracic multidetector CT

PURPOSE

We aimed to determine the prevalence of paratracheal air cysts (PTACs) and the relationship of PTACs with emphysema and bronchiectasis through retrospective analysis of multidetector computed tomography (MDCT) findings.

METHODS

MDCT findings of 1027 consecutive patients who underwent routine thorax examination between January 2012 and January 2013 were evaluated retrospectively for the presence of PTACs. Localization of the PTACs, as well as their size, shape, and relationship with the trachea were examined. Presence of emphysema and bronchiectasis was recorded, and bronchiectasis severity index was calculated when present. We randomly selected 80 patients who had no visible PTACs as the control group. The findings of patients with and without PTACs were compared.

RESULTS

PTACs were determined in 82 of 1027 patients (8%), in 8.8% of females and 7.3% of males. The presence of PTACs was determined to be independent of gender (P = 0.361). Eighty-one PTACs (98.8%) were located in the right side of the trachea and 56.1% had a tracheal connection. The presence of PTACs significantly correlated with the presence and severity of bronchiectasis (P = 0.001 and P = 0.005 respectively). There was no significant relationship between the presence of PTACs and the presence of emphysema on CT images (P = 0.125).

CONCLUSION

The prevalence of PTACs was determined as 8% in this study. There was significant association between PTACs and bronchiectasis.Paratracheal air cysts (PTACs) are small collections of air adjacent to the trachea at the level of the thoracic inlet (1). Pathological diagnosis of PTACs in surgically confirmed cases includes tracheal diverticulum, lymphoepithelial cyst, and bronchogenic cyst (1–3). These cysts are covered with ciliary columnar epithelium and connected with the trachea (4). The majority of PTACs are reported as tracheal diverticula in the literature, due to their connection with the trachea (2). The thoracic inlet between the cartilage and muscle layers in right posterolateral wall of the trachea is the most common location for PTACs. A relationship may be seen between an isolated PTAC and the trachea l lumen (5). These lesions may cause recurrent infections by acting as a reservoir for secretions.Occasionally, PTACs can be confused with other causes of extraluminal air collections as laryngocele, pharyngocele, Zenker’s diverticulum, apical hernia of the lung, mediastinal air, apical paraseptal blebs, or bullae. To distinguish PTACs from other pathologies, its typical location in the right posterior paratracheal region at the thoracic inlet can be helpful: PTACs locate away from the lung pleura, communicate with the trachea and have rounded margins that can be differentiated from emphysematous changes (6).PTACs are usually discovered incidentally on thorax computed tomography (CT). They may be associated with a chronic cough or chronic obstructive pulmonary diseases (COPD). The reported prevalence of PTACs ranges from 0.75% to 8.1% (4, 6–8). There have been a limited number of studies reporting the incidence of PTACs related to COPD or emphysema as detected by CT, and the reported results are variable (4, 6, 8–11). The relationship between PTACs and pulmonary emphysema or bronchiectasis is still unclear. To our knowledge, no published study has evaluated the relationship between PTACs and bronchiectasis, using a bronchiectasis severity index and objective measures to determine the extent of bronchiectasis on CT images.The purpose of our study was to evaluate the prevalence and characteristics of PTACs, as well as their relationship with bronchiectasis and emphysema, on thorax CT scans.     

Melatonin ameliorates chronic renal failure-induced oxidative organ damage in rats

Chronic renal failure (CRF) is associated with oxidative stress that promotes production of reactive oxygen species (ROS). Melatonin, the chief secretory product of the pineal gland, was recently found to be a potent free radical scavenger and antioxidant. The aim of this study was to examine the role of melatonin in protecting the aorta, heart, corpus cavernosum, lung, diaphragm, and kidney tissues against oxidative damage in a rat model of CRF, which was induced by five of six nephrectomy. Male Wistar albino rats were randomly assigned to either the CRF group or the sham-operated control group, which had received saline or melatonin (10 mg/kg, i.p.) for 4 wk. CRF was evaluated by serum blood urea nitrogen (BUN) level and creatinine measurements. Aorta and corporeal tissues were used for contractility studies, or stored along with heart, lung, diaphragm, and kidney tissues for the measurement of malondialdehyde (MDA, an index of lipid peroxidation), protein carbonylation (PC, an index for protein oxidation), and glutathione (GSH) levels (a key antioxidant). Plasma MDA, PC, and GSH levels and erythrocytic superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities were studied to evaluate the changes of antioxidant status in CRF. In the CRF group, the contraction and the relaxation of aorta and corpus cavernosum samples decreased significantly compared with controls (P < 0.05-0.001). Melatonin treatment of the CRF group restored these responses. In the CRF group, there were significant increases in tissue MDA and PC levels in all tissues with marked reductions in GSH levels compared with controls (P < 0.05-0.001). In the plasma, while MDA and PC levels increased, GSH, SOD, CAT, and GSH-Px activities were reduced. Melatonin treatment reversed these effects as well. In this study, the increase in MDA and PC levels and the concomitant decrease in GSH levels of tissues and plasma and also SOD, CAT, GSH-Px activities of plasma demonstrate the role of oxidative mechanisms in CRF-induced tissue damage, and melatonin, via its free radical scavenging and antioxidant properties, ameliorates oxidative organ injury. CRF-induced dysfunction of the aorta and corpus cavernosum of rats was reversed by melatonin treatment. Thus, supplementing CRF patients with adjuvant therapy of melatonin may have some benefit.     

The association of primary hyperparathyroidism and primary ovarian failure: a de novo t(X; 2) (q22p13) reciprocal translocation

CASE: A 40-year-old female presented with primary amenorrhoea at 17 years of age. She was tall at 98th centile for height with eunuchoidal body habitus. Her breast development was Tanner stage 3, pubic and axillary hair Tanner stage 4 with normal external genitalia. Her bone age was 13.4 years at a chronological age of 17.8 years. Gonadotrophins were elevated indicating primary ovarian failure. A diagnostic laparotomy revealed hypoplastic, infantile uterus with bilateral streak gonads. Chromosomal analysis showed a balanced reciprocal translocation 46X, t(X; 2) (q22 p13). She became pregnant by in vitro fertilization with egg donation at the age of 36 years. At 13 weeks of gestation, she presented with intractable vomiting. She had raised corrected serum calcium and parathyroid hormone concentrations consistent with the diagnosis of primary hyperparathyroidism (PHPT). She underwent parathyroidectomy at 24 weeks of gestation with removal of a large left inferior parathyroid adenoma which normalized her serum calcium. Multipoint linkage from a genome-wide screen has identified a region of suggestive linkage on chromosome 2p13.3-14 in some cases of familial isolated hyperparathyroidism (FIHP). CONCLUSION: To our knowledge, this is the first case of primary amenorrhoea due to reciprocal translocation involving chromosome 2 and the X chromosome associated with PHPT. PHPT in this case is most likely to be as a result of chromosome 2 involvement where a locus for FIHP has been identified. Identification of the gene involved on chromosome 2p13.3-14 will be of considerable interest.     

Apnea‐related sleep fragmentation and poor vigilance in children with well‐controlled asthma

It has been reported that sleep problems and neurocognitive deficit in asthmatic children is prevalent. However, systematic studies on these problems in stable asthma using polysomnography have rarely been performed. We therefore investigated sleep and neurocognitive functioning in children with well‐controlled asthma. Forty‐three children with well‐controlled, stable asthma and 31 controls (age range: 6–9 years) were enrolled in the study. Subjects were questioned for daytime sleepiness using the Paediatric Daytime Sleepiness Scale. Complete overnight polysomnography and neurocognitive function tests were performed on all subjects. Children with stable asthma had lower pulmonary function in comparison to their age‐matched controls. Asthmatic children had a higher apnea–hypopnea index (P < 0.001) and apnea–hypopnea‐related arousal index (P < 0.001) as compared with non‐asthmatics. Deep sleep was decreased in asthmatics (P = 0.001). In the vigilance test, the mean number of correct answers was lower (P = 0.005) and the mean reaction time was slower (P = 0.002) in asthmatic children. A hierarchical multiple linear regression showed that deep sleep and apnea–hypopnea‐related arousal index were significant predictors of vigilance. The data suggest that the prevalence of paediatric sleep‐disordered breathing and sleep fragmentation could be very high among children with well‐controlled asthma. Moreover, vigilance, the ability to maintain attention and alertness, was worse in stable asthmatic children when compared with healthy controls. Sleep‐disordered breathing should be checked even in stable asthmatic children as they are at risk for developing neurobehavioural deterioration associated with frequent arousals during sleep. Furthermore, early treatment for asthma may be required in order to prevent airway remodelling that could cause sleep problems.     

Hypertensive response to exercise in dipper and non-dipper normotensive diabetics

Non-dipper blood pressure (NDP) as an indicator of autonomic dysfunction could be associated with hypertensive response to exercise (HRE) in diabetic patients. HRE was determined as a predictor of development of unborn hypertension. We aimed to investigate if any correlation among NDP and HRE in normotensive type 2 diabetic patients. A total of 59 consecutive type 2 diabetic patients without history of hypertension and with normal blood pressure (BP) on ambulatory blood pressure monitoring (ABPM) were enrolled to the study. We divided the study population in to two groups depending on their BP on ABPM as dipper (group 1) or non-dipper (group 2). There were 22 patients (mean age 49.5?±?7 and 10 male) in group 1 and 37 patients (mean age 53.1?±?10 and 14 male) in group 2. Daytime diastolic and mean BP of dippers and night time systolic and mean BP of non-dippers were significantly higher. HRE was not significantly different between groups (59% vs. 62%, p?=?0.820). Hemodynamic parameters during the exercise test were similar. At multivariate linear regression analysis, resting office systolic blood pressure (SBP) (r?=?0.611, p?r?=?0.266, p?=?0.002) and age (r?=?0.321, p?=?0.010) were independently correlated with peak exercises SBP. Logistic regression analyses identified the resting office SBP (OR 1.191, 95% CI 1.080–1.313; p?p?=?0.012) were independent predictors of HRE. This study revealed that HRE is not related with non-dipper BP in diabetic patients. This study could inspire to further studies to explore the main reasons of HRE in diabetes mellitus.     

Risk factors for avascular bone necrosis in patients with systemic lupus erythematosus

The objective was to investigate the predictive factors for avascular necrosis (AVN) of bone in patients with systemic lupus erythematosus (SLE). The records of 868 patients with SLE from four centers were reviewed retrospectively. Forty-nine patients with AVN were identified. A total of 154 patients with SLE who did not have clinically apparent AVN during the follow-up were evaluated as a control group. The demographic, clinical, laboratory and management characteristics of these two groups of patients were recorded according to predefined protocol and compared. The prevalence of AVN was detected 6% in our SLE population. The highest dose corticosteroid administered within 4?months and total cumulative prednisolone dose were significantly higher in the SLE patients with AVN. The use of cytotoxic agent significantly higher proportion of patients with AVN. AVN tends to develop more frequently in male gender and younger patients. Oral ulcer, pleuritis, Raynaud??s phenomenon, cutaneous vasculitis, lymphadenopathy, autoimmune thyroiditis, peripheral neuropathy and Sj?gren??s syndrome were higher incidence in SLE patients with AVN. The bilateral femoral heads were the commonest site of involvement of AVN in our patients with SLE.     

Primary Malignant Melanoma of the Oesophagus

Primary malignant melanoma arising in the oesophagus is a rare condition with a dismal prognosis. The diagnosis is often made following surgical resection even though the endoscopic features may be pathognomonic. The classical treatment is oesophagectomy even though the advanced disease stage at the time of presentation and aggressive biological behaviour of the tumour usually results in a fatal outcome. We report the case of a male patient initially diagnosed with squamous oesophageal carcinoma and treated with conventional neo-adjuvant chemo-radiotherapy. Poor clinical and radiological response resulted in a review of the original histology confirming a diagnosis of primary malignant melanoma of the oesophagus. The subsequent alteration in management conferred the patient an improved quality of life. A short review of the literature on primary malignant melanoma of the oesophagus supplements this case report.