Accurate density functional theory prediction of low-dimensional yttrium nitride: From 2D hexagonal and square monolayers to 1D zizag single walled nanotubes

Through this contribution, we aim to highlight the structural stability of low dimensional YN structures ranging from the 3D bulk to the 2D square and hexagonal monolayers and their corresponding 1D zigzag single walled nanotubes. For all arrangements, geometry optimization is achieved at the DFT/B3LYP level of theory using a Gaussian basis set. Then, the coupled perturbed Kohn-Sham and Hartree-Fock (CPKS/HF) computational approach is used to simulate Raman and IR spectrum. Rolling, cohesive and relaxation energies, electronic and vibrational contributions to the polarizability and equilibrium lattice parameters are also reported. Insights into their structural stability are provided by combining optimized parameters and vibrational phonon spectra. For the optimized 3D bulks, 2D monolayers and 1D square nanotubes, no imaginary frequency has been recorded in their vibrational spectra which reveals a dynamic stability. Likewise, imaginary frequencies appeared only for relatively large YN (n,0) single walled hexagonal nanotubes (n > 6) indicating that the optimized structures are not a real global minimum and implying a dynamic instability. A scaning mode procedure along the largest imaginary vibrational mode has been adopted to obtain the equilibrium geometry of (22,0) YN hexagonal nanotube. Therefore, it must be emphasized that the obtained potential energy surface presents two minima between a saddle point. These minima corresponds to a stable structures slightly distorted compared to the initial one. The absence of imaginary phonon frequencies in the Raman and IR spectra of the optimized (22,0) YN hexagonal nanotube confirms its structural stability.

AB0485 TRIGGERS OF DISEASE FLARES IN SYSTEMIC LUPUS ERYTHEMATOSUS

Background

Systemic lupus erythematosus (SLE) is a chronic relapsing-remitting disease characterized by a clinical heterogeneity, an unpredictable pattern and a capricious course. Despite great advances in diagnosis and treatment strategies, lupus flares of varying severity still occur, leading to an increased risk of organs damages and a poorer prognosis. Preventing flares, achieving and maintaining remission represent the main objective in SLE management and remain a major challenge for practitioners.

Objectives

Our study aimed to describe lupus flare-ups and identify its triggering factors, in a cohort of patients with active SLE, in order to optimize disease control.

Methods

We conducted a retrospective study including patients with SLE followed for a period of 20 years. SLE diagnosis was retained according to the American college of Rheumatology classification criteria (ACR) of 1997 and/or to the SLICC 2012 criteria. A lupus flare was defined by the occurrence of new or worsening lupus manifestation, justifying treatment intensification. We evaluated potential flare triggers, disease activity at each outbreak according to the SLEDAI-2K score and flare types. Patients considered at full clinical remission or at low disease activity state (SLEDAI ≤ 3 in patients treated with antimalarials drugs / SLEDAI ≤ 4 in patients treated with a low glucocorticoids dose <7.5 mg of Prednisone per day ± immunosuppressant) during the study period were excluded (31/102; 30.4% of patients).

Results

A total of 72 patients, with a mean age at SLE diagnosis of 31 years [11-66] and a gender ratio (F/M) of 8:1, were enrolled. During follow-up, 186 flares occurred. The average number of flares per patient was 3 [1-13]. The mean SLEDAI score during flare-ups was 8 [6-21]. At least one triggering factor was found in 62.9% of flares. The identified triggers for lupus flares were medication nonadherence in 54.7% of cases (discontinuation of antimalarial drugs and corticosteroid therapy in 38.46% and 16.2% of cases, respectively), an intercurrent infection in 30.7% of cases, a hormonal factor in 11.96% and inadequate photoprotection and/or excessive sun exposure in 8.5% of flares. Elsewhere, lupus flare-ups could be explained by therapeutic inertia or corticosteroid dependence (mean dose of 12.5mg per day) in 3.4% and 13.7 % of cases, respectively. Frequencies of general symptoms, cutaneous and haematological flare-ups were higher in relapses with objectified triggering factors (26.5% vs 8.7%, p=0.02; 40.2% vs 26.1%, p=0.036; 32.5% vs 14.5%, p=0.005). In contrast, renal flare-ups were more frequent in the group of flares in which no triggering factors were identified (21.4% vs 33.3%, p=0,005). Disease activity was comparable in both groups. The average follow-up time was 8 years [1-26].

Conclusion

In our cohort, an avoidable trigger, dominated by poor medication compliance and infections, preceded more than one out of two lupus flares. Formalized and organized therapeutic education should be one of the pillars of SLE management.

Disclosure of Interests

None declared

[A rare cause of pulmonary arterial hypertension: Thoracic amyloidosis]

Isolated thoracic involvement in amyloidosis is a rare and serious condition. Its association with pulmonary arterial hypertension (PAH) usually weakens the prognosis. We report the case of a 40-year-old man with a smoking history, hospitalized for chest pain, abdominal pain and acute respiratory distress. The cardiac ultrasound revealed a circumferential pericardial effusion as well as a pulmonary artery systolic pressure (PAPS) at 80mmHg. Chest imaging (computed tomography scan and magnetic resonance imaging) showed a tissue process developed in the pericardial sheath (60×45mm) sheathing the ascending aorta and infiltrating the trunk of the pulmonary artery and its right branch. Anatomopathological and immunohistochemical study of the process revealed AL amyloidosis. Note that the patient had no signs of extrathoracic amyloidosis. Blood and urine electrophoresis and immunoelectrophoresis as well as bone marrow mylogram and biopsy were normal. The patient was put on oral anticoagulant as he presented with PAH. A therapeutic protocol with thalidomide and dexamethasone has been initiated. The course of the disease was marked by total regression of the clinical signs, a marked decrease in the amyloid process on imaging and a normalization of the PAPS; our follow-up being three years.

[Characteristics of cardiac involvement in eosinophilic granulomatosis with polyangiitis]

AIM OF THE STUDY

Our study aimed to identify the characteristics of cardiac involvement in eosinophilic granulomatosis with polyangiitis (EGPA).

METHODS

We conducted a retrospective analytic study including EGPA cases diagnosed between 2000 and 2019 in an internal medicine department. Diagnosis was made according to the 1990 American College of Rheumatology criteria and the 2012 Chapel Hill Concensus.

RESULTS

Eleven EGPA cases were included, 64% of patients were female. Median age at diagnosis was 52 years [42-58]. Heart damage revealed EGPA in 55% of cases with a significant predominance of women (p=0.015). The main cardiac manifestations were myocarditis, ischemic cardiomyopathy due to small vessel vasculitis, cardiac tamponade and intracardiac thrombus. Cardiac magnetic resonance imaging (MRI) mainly showed subendocardial hyposignal in early infusion and late enhancement in the same areas, nodular by locations, associated with impaired left ventricle function and micro-infarctions by distal vasculitis. Cardiac damage was associated to ANCA negativity in 83.3% of cases. The median Birmingham Vasculitis Activity Score version3 (BVAS v3) was 16 [10-17]. Under conventional treatment, no relapses had occurred. The median vasculitis damage index (VDI) was 2 [1-2.3] and the mortality rate was zero after a mean follow-up of 43 months.

CONCLUSION

Cardiomyopathy is a frequent revealing mode of EGPA. A late onset asthma and hypereosinophilia should guide the diagnosis. As ANCA research often turns out to be negative, histological evidence is recommended in this context. The contribution of cardiac MRI in the diagnosis of EGPA remains to be defined.

Temperature dependence of Raman spectra and first principles study of NiMn2O4 magnetic spinel oxide thin films. Application in efficient photocatalytic removal of RhB and MB dyes

Magnetic spinel oxide NiMn₂O₄ thin films were grown on glass substrates using the spray pyrolysis deposition technique at 350 °C. First, structural optimization, electronic structure and vibrational properties were obtained for NiMn₂O₄ by density functional theory (DFT) with an all electron basis set and the hybrid functional B3LYP implemented in the CRYSTAL14 code. Our DFT results show good agreement with previous experimental and theoretical data. Second, Raman spectra of as-prepared thin films have been measured over the temperature range from 100 K to 620 K. We report on the temperature dependence of their dominant first-order scattering F_2g and A_1g phonons modes. The phonon dynamic behavior is well described by a model taking into account explicit lattice anharmonicity associated to both cubic and quartic phonon decay processes and thermal expansion related quasiharmonicity. Finally, the photocatalytic activities of the obtained thin films were evaluated through the photocatalytic degradation of Rhodamine B (RhB) and methylene blue (MB) solutions under solar light irradiation as a function of time. All the results indicate that NiMn₂O₄ thin film can be used as a potential solar-light-driven photocatalyst.