Magnetic anisotropy, magnetization reversal and switching in Ni4Nb2O9single crystals

Ni4Nb2O9is an insulating compensated ferrimagnet withTN= 77 K andTcomp= 33 K. We report here the study of the magnetic anisotropy using millimeter-size crystals grown in an image furnace. The magnetization measurements, vs temperature, performed withHaligned along the three main crystallographic axes, show similar Curie-Weiss temperatures (Θp≈ 190 K) and rather similar effective paramagnetic moments (from 3.5μBto 3.6μB). This suggests that the strongest magnetic interaction is the antiferromagnetic one, coupling the ferromagnetic distorted honeycomb layers and zigzag ribbons via face sharing NiO6octahedra. This strong antiferromagnetic coupling is supported by DFT calculations that do not evidence any inter site ferromagnetic interaction, leading to total compensation between magnetic moments of both Ni2+sites. Measurements vs magnetic field belowTNreveal an anisotropic behaviour, with square magnetization loops forHin theabplane, whereas linearM(H) curves without hysteresis are observed forH‖c. This anisotropy betweenabplane andcaxis occurs also in the magnetization reversal (MR), which is observed in theabplane only. Starting fromM(H) virgin curves collected just belowTcomp= 33 K withH‖aorH‖b, the memory-like effect was tested through magnetization switching induced byHorTalternating changes. BelowTcomp, smallerHis needed to switchMsymmetrically forHalongbthan alonga, and, forTswitching (2 K interval, constantH), a largerMchange is obtained alongathan alongb. The comparison with ferrimagnetic oxides which exhibit MR, like spinels or rare earth orthoferrites, shows that Ni4Nb2O9is unique since only one magnetic cation over two sites in octahedral coordination is at play, thus providing a unique platform to studyMswitching but also a challenge for theoretical interpretation.

Long-term results of dynamic graciloplasty for severe fecal incontinence

BACKGROUND

Fecal incontinence is a common complaint. In the presence of extensive sphincter deterioration, after anorectal trauma, or failure of non-invasive surgical procedures, a sphincter reconstruction with dynamic graciloplasty can be proposed. The aim of our study was to evaluate the long-term results of dynamic graciloplasty.

METHODS

A retrospective study was conducted on all the patients who underwent dynamic graciloplasty between 1997 and 2019 in one French tertiary referral center for severe fecal incontinence after previous unsuccessful treatments. Only patients with available long-term results (≥ 1 year) were included.

RESULTS

Among 40 patients who underwent dynamic graciloplasty, 31 patients [77% women, median age = 57 years (range 17-74 years)] were included with a mean long-term follow-up of 11 ± 6 years. The mean duration of fecal incontinence was 8 ± 7.9 years and the mean Wexner score was 16 ± 3. Fecal incontinence was adult-acquired in 88% of patients. 74% of patients underwent previously unsuccessful surgical procedures. A diverting colostomy was present in 7 patients (23%). Postoperative overall, surgical and major morbidity occurred in 20 (64%), 17 (55%) and 7 (23%) patients, respectively. At the end of follow-up, 18 patients still used their stimulation device (58%), and 4 patients required a permanent colostomy (12.5%). Long-term efficacy of dynamic graciloplasty was reported by 17 patients (55%).

CONCLUSION

The efficacy of dynamic graciloplasty is conserved in 55% of patients after a mean follow-up of 11 years. This procedure needs to be kept in the surgical armamentarium for persistent and severe fecal incontinence after previous surgical interventions or in the presence of large perineal defects, before the ultimate step of permanent stoma.

Value of early repeated abdominal CT in selective non-operative management for blunt bowel and mesenteric injury

OBJECTIVES

To evaluate the performance of an early repeated computed tomography (rCT) in initially non-operated patients with blunt bowel and mesenteric injuries (BBMI).

METHODS

This was a monocentric retrospective observational study from 2009 to 2017 of patients with a BBMI on initial CT (iCT). Patients initially non-operated on were scheduled for a rCT within 48 h. Initial CT and rCT diagnostic performance were compared based on a surgical injury prediction score previously described. For statistical analysis, we used the chi-square analyses for paired data (McNemar test).

RESULTS

Eighty-four patients (1.9% of trauma) had suspected BBMI on iCT. Among these patients, 22 (26.2%) were initially operated on, 18 (21.4%) were later operated on, and 44 (52.4%) were not operated on. The therapeutic laparotomy rate was 85%. Thirty-four patients initially non-operated on had a rCT. The absolute value of the CT scan score increased for 15 patients (44.1%). The early rCT diagnostic performance, compared with iCT, showed an increase in sensitivity (from 63.6 to 91.7%), in negative predictive value (from 77.4 to 94.7%), and in AUC (from 0.77 to 0.94).

CONCLUSION

In initially non-operated patients with BBMI lesions, the performance of an early rCT improved the sensitivity of lesion detection requiring surgical repair and the security of patient selection for non-operative treatment.

KEY POINTS

• Selective non-operative treatment for hemodynamically stable patients with blunt bowel and/or mesenteric injuries on CT is developing but remains controversial. • An early repeated CT improved the sensitivity of lesion detection requiring surgical repair and the security of patient selection for conservative treatment.

Risk factors of exocrine and endocrine pancreatic insufficiency after pancreatic resection: A multi-center prospective study

Management of functional consequences after pancreatic resection has become a new therapeutic challenge. The goal of our study is to evaluate the risk factors for exocrine (ExoPI) and endocrine (EndoPI) pancreatic insufficiency after pancreatic surgery and to establish a predictive model for their onset.

PATIENTS AND METHODS

Between January 1, 2014 and June 19, 2015, 91 consecutive patients undergoing pancreatoduodenectomy (PD) or left pancreatectomy (LP) (72% and 28%, respectively) were followed prospectively. ExoPI was defined as fecal elastase content<200μg per gram of feces while EndoPI was defined as fasting glucose>126mg/dL or aggravation of preexisting diabetes. The volume of residual pancreas was measured according to the same principles as liver volumetry.

RESULTS

The ExoPI and EndoPI rates at 6 months were 75.9% and 30.8%, respectively. The rate of ExoPI after PD was statistically significantly higher than after LP (98% vs. 21%; P<0.001), while the rate of EndoPI was lower after PD vs. LP, but this difference did not reach statistical significance (28% vs. 38.5%; P=0.412). There was no statistically significant difference in ExoPI found between pancreatico-gastrostomy (PG) and pancreatico-jejunostomy (PJ) (100% vs. 98%; P=1.000). Remnant pancreatic volume less than 39.5% was predictive of ExoPI.

CONCLUSION

ExoPI occurs quasi-systematically after PD irrespective of the reconstruction scheme. The rate of EndoPI did not differ between PD and LP.

A pancreatic ductal adenocarcinoma subpopulation is sensitive to FK866, an inhibitor of NAMPT

Treating pancreatic cancer is extremely challenging due to multiple factors, including chemoresistance and poor disease prognosis. Chemoresistance can be explained by: the presence of a dense stromal barrier leading to a lower vascularized condition, therefore limiting drug delivery; the huge intra-tumoral heterogeneity; and the status of epithelial-to-mesenchymal transition. These factors are highly variable between patients making it difficult to predict responses to chemotherapy. Nicotinamide phosphoribosyl transferase (NAMPT) is the main enzyme responsible for recycling cytosolic NAD⁺ in hypoxic conditions. FK866 is a noncompetitive specific inhibitor of NAMPT, which has proven anti-tumoral effects, although a clinical advantage has still not been demonstrated. Here, we tested the effect of FK866 on pancreatic cancer-derived primary cell cultures (PCCs), both alone and in combination with three different drugs typically used against this cancer: gemcitabine, 5-Fluorouracil (5FU) and oxaliplatin. The aims of this study were to evaluate the benefit of drug combinations, define groups of sensitivity, and identify a potential biomarker for predicting treatment sensitivity. We performed cell viability tests in the presence of either FK866 alone or in combination with the drugs above-mentioned. We confirmed both inter- and intra-tumoral heterogeneity. Interestingly, only the in vitro effect of gemcitabine was influenced by the addition of FK866. We also found that NAMPT mRNA expression levels can predict the sensitivity of cells to FK866. Overall, our results suggest that patients with tumors sensitive to FK866 can be identified using NAMPT mRNA levels as a biomarker and could therefore benefit from a co-treatment of gemcitabine plus FK866.

Pancreatic Adenocarcinoma Therapeutic Targets Revealed by Tumor-Stroma Cross-Talk Analyses in Patient-Derived Xenografts

Preclinical models based on patient-derived xenografts have remarkable specificity in distinguishing transformed human tumor cells from non-transformed murine stromal cells computationally. We obtained 29 pancreatic ductal adenocarcinoma (PDAC) xenografts from either resectable or non-resectable patients (surgery and endoscopic ultrasound-guided fine-needle aspirate, respectively). Extensive multiomic profiling revealed two subtypes with distinct clinical outcomes. These subtypes uncovered specific alterations in DNA methylation and transcription as well as in signaling pathways involved in tumor-stromal cross-talk. The analysis of these pathways indicates therapeutic opportunities for targeting both compartments and their interactions. In particular, we show that inhibiting NPC1L1 with Ezetimibe, a clinically available drug, might be an efficient approach for treating pancreatic cancers. These findings uncover the complex and diverse interplay between PDAC tumors and the stroma and demonstrate the pivotal role of xenografts for drug discovery and relevance to PDAC.

Temporary successful results of ventral rectopexy for enterocele surgical correction, about 138 patients

PURPOSE

This work aimed to analyse short- and long-term results of enterocele surgical treatment by ventral rectopexy.

METHODS

All females who underwent ventral rectopexy for enterocele in our department were included. All patients underwent standardized preoperative evaluation. Data was retrospectively collected, after examination of patients or by telephone survey. Postoperative evaluation was performed by an independent observer.

RESULTS

One hundred thirty-eight females (median age = 63 years [21-86 years]) were included. They were postmenopausal and multiparous in 94 and 70% of cases, respectively. Pelvic pressure, vaginal prolapse, or the both were observed in 28, 16 or 56% of the patients, respectively. The most frequent associated symptoms were dyschezia (63%) and faecal incontinence (30%). On preoperative workup, enterocele was isolated in two cases. Rectocele, internal rectal prolapse and cervicocystoptosis were the most frequently associated pelvic floor disorders. Ventral rectopexy was performed through laparoscopy in 128 patients (93%). In the short term, all pelvic symptoms were significantly improved, except urinary incontinence. At the end of follow-up (56 months [7-125]), specific symptoms and dyschezia were still significantly improved. Secondary failure was reported in 31% of patients. By multivariate analysis, two predictive factors for long-term failure were found: diagnosis of rectocele on preoperative MRI (odd ratio = 15; 95% CI 1.4-163; p = 0.03) and conversion into open surgery (odd ratio = 8; 95% CI 1.4-43; p = 0.02).

CONCLUSION

This study suggests that ventral rectopexy is an effective treatment of enterocele, but secondary failure can be observed. Patients should be informed of the potential risk of long-term degradation.

Gene expression profiling of patient-derived pancreatic cancer xenografts predicts sensitivity to the BET bromodomain inhibitor JQ1: implications for individualized medicine efforts

c-MYC controls more than 15% of genes responsible for proliferation, differentiation, and cellular metabolism in pancreatic as well as other cancers making this transcription factor a prime target for treating patients. The transcriptome of 55 patient-derived xenografts show that 30% of them share an exacerbated expression profile of MYC transcriptional targets (MYC-high). This cohort is characterized by a high level of Ki67 staining, a lower differentiation state, and a shorter survival time compared to the MYC-low subgroup. To define classifier expression signature, we selected a group of 10 MYC target transcripts which expression is increased in the MYC-high group and six transcripts increased in the MYC-low group. We validated the ability of these markers panel to identify MYC-high patient-derived xenografts from both: discovery and validation cohorts as well as primary cell cultures from the same patients. We then showed that cells from MYC-high patients are more sensitive to JQ1 treatment compared to MYC-low cells, in monolayer, 3D cultured spheroids and in vivo xenografted tumors, due to cell cycle arrest followed by apoptosis. Therefore, these results provide new markers and potentially novel therapeutic modalities for distinct subgroups of pancreatic tumors and may find application to the future management of these patients within the setting of individualized medicine clinics.

Abstract 4396: Multiomics assessment of the cancer and stromal compartments of patient-derived pancreatic xenografts reveals clinically-relevant subtypes and novel targeted therapies

Patient-derived xenografts (PDX) are appearing as a prime approach for preclinical studies despite being insufficiently characterized as a model of the human disease and its diversity. In this work, 29 PDX were obtained from either surgery or endoscopic ultrasound-guided fine needle aspirate of pancreatic adenocarcinoma. The extensive genomic profiling of these pancreatic PDX, revealed two clinically-relevant subtypes having broad similarities with human primary tumors. These subtypes are defined by highly specific DNA methylation and transcriptomic profiles (mRNA, miRNA or lncRNA) but are not distinguishable by exonic mutations or copy number aberrations. Moreover, by specifically analyzing the stroma transcriptome, as defined by the expression of murine transcripts, we found that it is able to stratify the patients with the same efficiency than the analysis of grafted human tumor cells. This finding suggest that transformed pancreatic cells drive the composition of their own stroma. Finally, the multiomics analysis pinpoints novel therapeutic targets, one of which we demonstrate to be an efficient method for treating pancreatic cancer. Overall, we show that PDX are trustworthy pre-clinical models of pancreatic adenocarcinoma including of unresectable tumors. Their multiomics profiling allow the independent analysis of the uncontaminated cancer or stromal compartments and discloses several original therapeutics targets.

Citation Format: Remy Nicolle, Yuna Blum, Laetitia Marisa, Celine Loncle, Odile Gayet, Vincent Moutardier, Olivier Turrini, Marc Giovannini, Benjamin Bian, Martin Bigonnet, Marion Rubis, Nabila Elarouci, Lucile Armenoult, Mira Ayadi, Pauline Duconseil, Mohamed Gasmi, Mehdi Ouaissi, Aurélie Maignan, Gwen Lomberk, Jean-Marie Boher, Jacques Ewald, Erwan Bories, Jonathan Garnier, Anthony Goncalves, Flora Poizat, Jean-Luc Raoul, Veronique Secq, Stephane Garcia, Philippe Grandval, Marine Barraud-Blanc, Emmanuelle Norguet, Marine Gilabert, Jean-Robert Delpero, Julie Roques, Ezequiel Calvo, Fabienne Guillaumond, Sophie Vasseur, Raul Urrutia, Aurélien de Reyniès, Nelson Dusetti, Juan Iovanna. Multiomics assessment of the cancer and stromal compartments of patient-derived pancreatic xenografts reveals clinically-relevant subtypes and novel targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4396. doi:10.1158/1538-7445.AM2017-4396

Abstract A48: Multi-omics characterization of PDAC subtypes using PDX reveals that epigenetic but not genetic analysis permit a clinically relevant classification

Genome-wide molecular profiles have been proven to be beneficial for the identification of clinically relevant tumor subtypes in many neoplastic diseases. While pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death, very few genomic and transcriptomic studies have been conducted. This is mainly due to the difficulty to obtain a suitable cohort of PDAC tumor samples. The major obstacle is the usually high proportion of non-transformed stromal cells, which can greatly hinder the analysis of carcinogenic-specific processes. Moreover, tumor cohorts requiring resection samples can be biased by the exclusion of inoperable patients, representing 85% of all patients presenting PDAC.

In this study, we generated Patient Derived Xenografts (PDX) with samples collected from 29 patients using either Endoscopic Ultrasound-Guided Fine-Needle Aspirates or, for operable patients, resections. The transcriptomic profiles, of both mRNA and miRNA, and the epigenetic landscape of early PDX passages consistently identified two tumor-specific molecular subtypes: a well differentiated group often referred to as classical, and an undifferentiated group previously recognized as Basal, Quasi-Mesenchymal or Squamous. Of all the genetic alterations determined by Copy Number analysis and exome sequencing, none were specific to any of the two subtypes, which therefore could not be discriminated solely on genetic basis.

These two PDAC subtypes are characterized by distinct epigenetic and transcriptomic profiles of which the analysis revealed the deregulation of several pathways previously imputed in PDAC development and carcinogenesis in general. In particular, we showed that the Wnt pathway as well as several metabolic pathways, including cytochrome P450 genes recently implicated in drug resistance, are both epigenetically and transcriptionally deregulated. Altogether, our results provide new insights on pancreatic carcinogenesis and suggest that PDAC phenotypical heterogeneity is mainly driven by epigenetic rather than genetic events.

Citation Format: Remy Nicolle, Yuna Blum, Laetitia Marisa, Jonathan Garnier, Benjamin Bian, Celine Loncle, Martin Bigonnet, Odile Gayet, Vincent Moutardier, Pauline Duconseil, Mohamed Gasmi, Mehdi Ouaissi, Olivier Turrini, Marc Giovannini, Aurélie Maignan, Jean-Marie Boher, Jacques Ewald, Erwan Bories, Marc Barthet, Anthony Goncalves, Flora Poizat, Jean-Luc Raoul, Veronique Secq, Stephane Garcia, Philippe Grandval, Marine Barraud-Blanc, Emmanuelle Norguet, Marine Gilabert, Jean-Robert Delpero, Ezequiel Calvo, Aurélien de Reyniès, Nelson Dusetti, Juan Iovanna.{Authors}. Multi-omics characterization of PDAC subtypes using PDX reveals that epigenetic but not genetic analysis permit a clinically relevant classification. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A48.

Abstract B72: Pancreatic cancer cell drives stroma composition

The extensive desmoplasia in pancreatic ductal adenocarcinoma (PDAC) has raised major interrogations on its role and function in the carcinogenic process. Patient-derived xenograft (PDX) offers an ideal setting to distinguish and to study the interactions between the cancerous epithelial cells and its stroma. Indeed, sequencing profiles of a mix of cancerous/Human and stroma/Mouse cells can be analyzed separately in silico by unambiguously assigning each sequence to the human or mouse genome. Using RNA sequencing, we profiled 30 pancreatic tumor PDXs and extracted the transcriptome profiles of epithelial cancerous cells as well as their corresponding stroma. On average, 70% of RNA sequencing reads were specifically attributed to a human origin, and therefore an epithelial origin, while 22% of RNA sequencing reads were mouse-specific. Using the rate of mouse sequences as a surrogate of the proportion of non-transformed cells, we observe a high variability in the infiltration level from 7% to 60%. The estimation was also consistent in whole exome sequencing (using the same sequencing process) and with the histological quantification of fibrotic tissue.

By specifically analyzing the gene expression in mouse-stromal cells, we show that their transcriptomic profile is consistent with the recent description of human PDAC in situ tumors with high levels of genes of the reported activated-stroma and normal-stroma signatures. We also show that stromal cells over-express genes involved in the SLIT/ROBO axon guidance signalling pathway, in angiogenesis as well as a large number of collagens, cytokines and ligands associated with growth and developmental pathways.

Recent studies identified two major subtypes of PDAC from transcriptomic analysis: a well differentiated, often referred as classical, and an undifferentiated, previously recognized as Basal, Quasi-Mesenchymal or Squamous. The stroma characterized in this work broadly reflects this heterogeneity with stromal gene expression signatures predictive of each subtype. For instance, collagens are significantly over-expressed in the stroma of squamous tumors. The concomitant analysis of transcriptomic profiles of both subtypes shows potential cross-talks between cancerous and stromal cells. Particularly in Squamous tumors, genes implicated in the axon-guidance and Wnt pathways are significantly upregulated in both, stroma and transformed cells. On the other hand, the stroma and transformed cells of Classical tumors shows an upregulation of complementary genes associated with several metabolic pathways.

Taken together, our transcriptomic analysis reveals that human transformed pancreatic cells determine the composition, quantitatively and qualitatively, of stroma mouse cells in a PDX model. This model also reveals a broad variability of PDAC stromas and highlights potential cross-talks between them through known and novel pathways.

Citation Format: Rémy Nicolle, Yuna Blum, Laetitia Marisa, Jonathan Garnier, Benjamin Bian, Celine Loncle, Martin Bigonnet, Odile Gayet, Vincent Moutardier, Pauline Duconseil, Mohamed Gasmi, Mehdi Ouaissi, Olivier Turrini, Marc Giovannini, Aurélie Maignan, Jean-Marie Boher, Jacques Ewald, Erwan Bories, Marc Barthet, Anthony Goncalves, Flora Poizat, Jean-Luc Raoul, Veronique Secq, Stephane Garcia, Philippe Grandval, Marine Barraud-Blanc, Emmanuelle Norguet, Marine Gilabert, Jean-Robert Delpero, Ezequiel Calvo, Aurélien de Reyniès, Juan Iovanna, Nelson Dusetti.{Authors}. Pancreatic cancer cell drives stroma composition. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B72.

A new active Li-Mn-O compound for high energy density Li-ion batteries

The search for new materials that could improve the energy density of Li-ion batteries is one of today's most challenging issues. Many families of transition metal oxides as well as transition metal polyanionic frameworks have been proposed during the past twenty years. Among them, manganese oxides, such as the LiMn2O4 spinel or the overlithiated oxide Li[Li1/3Mn2/3]O2, have been intensively studied owing to the low toxicity of manganese-based materials and the high redox potential of the Mn(3+)/Mn(4+) couple. In this work, we report on a new electrochemically active compound with the 'Li4Mn2O5' composition, prepared by direct mechanochemical synthesis at room temperature. This rock-salt-type nanostructured material shows a discharge capacity of 355 mAh g(-1), which is the highest yet reported among the known lithium manganese oxide electrode materials. According to the magnetic measurements, this exceptional capacity results from the electrochemical activity of the Mn(3+)/Mn(4+) and O(2-)/O(-) redox couples, and, importantly, of the Mn(4+)/Mn(5+) couple also.

Searching for new thermoelectric materials: some examples among oxides, sulfides and selenides

Different families of thermoelectric materials have been investigated since the discovery of thermoelectric effects in the mid-19th century, materials mostly belonging to the family of degenerate semi-conductors. In the last 20 years, new thermoelectric materials have been investigated following different theoretical proposals, showing that nanostructuration, electronic correlations and complex crystallographic structures (low dimensional structures, large number of atoms per lattice, presence of 'rattlers'…) could enhance the thermoelectric properties by enhancing the Seebeck coefficient and/or reducing the thermal conductivity. In this review, the different strategies used to optimize the thermoelectric properties of oxides and chalcogenides will be presented, starting with a review on thermoelectric oxides. The thermoelectric properties of sulfides and selenides will then be discussed, focusing on layered materials and low dimensional structures (TiS2 and pseudo-hollandites). Some sulfides with promising ZT values will also be presented (tetrahedrites and chalcopyrites).

On the effects of substitution, intercalation, non-stoichiometry and block layer concept in TiS2 based thermoelectrics

TiS₂ based layered sulfides have recently received increasing interest from the thermoelectric community.

Oesophagogastric reconnection is possible

INTRODUCTION

The first oesophagogastric dissociation was described by Bianchi in 1997 for the treatment of severe gastro-oesophageal reflux (GOR) in neurological patients to avoid serious respiratory complications. The dissociation leads to malabsorption and growth problems. We describe the first two cases of oesophagogastric reconnection long after lung growth.

PATIENTS

Case no. 1 was a 12.7-year-old child with a history of type I oesophageal atresia. He required oesophagocoloplasty and gastric dissociation by the Bianchi procedure at the age of 3 months. He has oesophagogastric reconnection at 11 years old because he had a several macrocytic anaemia. Case no. 2 was also a 12-year-old boy, with an unlabelled multiple malformation syndrome with type I oesophageal atresia. He had an oesophagocoloplasty with gastric dissociation at the age of 3 months to protect his lungs. The reconnection was proposed at 10 years old because he developed multiple nutritional deficiencies and growth retardation.

RESULTS

The two cases have no clinical symptom of reflux and their post-operative digestive contrasts are normal. Reconnection appears possible with or without preserving the Roux-en-Y loop. It improves absorption and corrects any vitamin deficiencies, allows the reconnected stomach to be monitored in terms of reflux and malignancy and enables enteral nutrition supplementation to be stopped. The possibility of reconnection after the Bianchi procedure therefore extends its indications, mostly in the case of oesophageal atresia complicated by severe GOR with pulmonary repercussions or tracheoesophageal cleft.

Oxygen storage capacity and structural flexibility of LuFe2O4+x (0≤x≤0.5)

Combining functionalities in devices with high performances is a great challenge that rests on the discovery and optimization of materials. In this framework, layered oxides are attractive for numerous purposes, from energy conversion and storage to magnetic and electric properties. We demonstrate here the oxygen storage ability of ferroelectric LuFe2O4+x within a large x range (from 0 to 0.5) and its cycling possibility. The combination of thermogravimetric analyses, X-ray diffraction and transmission electron microscopy evidences a complex oxygen intercalation/de-intercalation process with several intermediate metastable states. This topotactic mechanism is mainly governed by nanoscale structures involving a shift of the cationic layers. The ferrite is highly promising because absorption begins at a low temperature (~=200 °C), occurs in a low oxygen pressure and the uptake of oxygen is reversible without altering the quality of the crystals. The storage/release of oxygen coupled to the transport and magnetic properties of LnFe2O4 opens the door to new tunable multifunctional applications.

Sr7Co4(CO3)O(13-δ) (δ = 1.64), an original cobaltite derivative of the Ruddlesden-Popper series

The oxycarbonate Sr7Co4(CO3)O11.36 exhibits a peculiar structure that has been characterized by combining transmission electron microscopy analyses and neutron diffraction. It consists of a regular intergrowth between the m = 2 and carbonated m = 3 members of the Sr(m+1)Co(m)O3(m+1) Ruddlesden-Popper (RP) series, Sr3Co2O5.87 and Sr4Co2(CO3)O5.49, respectively. A description of the structure is proposed to provide identification of the different building blocks. This material is semiconducting and presents a complex magnetic behavior, characteristic of what is observed for the RP(2) or RP(3) series, with a cobalt valency close to 2.7.

Pressure-induced structural transition in LuFe2O4: towards a new charge ordered state

The electronic ferroelectric lutetium ferrite (LuFe(2)O(4)) was studied by x-ray diffraction as a function of pressure. Pressure is shown to induce an irreversible rhombohedral to orthorhombic transition leading to a supercell determined by the combination of electron and synchrotron x-ray diffraction. This new configuration is proposed to be charge ordered in agreement with the results of resistivity measurements.

Metallicity and positive magnetoresistance induced by Pb substitution in a misfit cobaltate crystal

We have synthesized single crystals of the misfit-layered cobalt oxide, [Bi(1.5)Pb(0.5)Sr(2)O(4-δ)][CoO(2)](1.86), with quadruple NaCl-type layers, using a flux method, and measured their transport properties. From structural refinements, it is found that the modulation in the BiO layer observed in [Bi(1.74)Sr(2)O(4-δ)](RS)[CoO(2)](1.82) is suppressed by Pb substitution. The in-plane resistivity, thermopower, and Hall coefficient are 4.3  mΩ cm, 101  µV K(-1), and 1 × 10(-2) cm(3) C(-1) at 300 K, respectively; these are consistent with those of the misfit-layered cobalt oxides. All of these values are smaller than those of [Bi(1.74)Sr(2)O(4)][CoO(2)](1.82), indicating that the carrier concentration is larger than that of the undoped crystal. Moreover, the low T upturn of resistivity observed for most of the cobalt misfit oxides is replaced by a metallic behavior, following a T(2) dependence, indicating strong correlations in the Pb-doped crystal. Also, the magnetoresistance, usually negative for misfit oxides, is replaced by a small positive magnetoresistance. Doping with Pb is thus an efficient way to suppress the low T localized behavior usually observed for misfits.

Ising magnetism and ferroelectricity in Ca3CoMnO6

The origin of both the Ising chain magnetism and ferroelectricity in Ca3CoMnO6 is studied by ab initio electronic structure calculations and x-ray absorption spectroscopy. We find that Ca3CoMnO6 has alternate trigonal prismatic Co2+ and octahedral Mn4+ sites in the spin chain. Both the Co2+ and Mn4+ are in the high-spin state. In addition, the Co2+ has a huge orbital moment of 1.7micro_{B} which is responsible for the significant Ising magnetism. The centrosymmetric crystal structure known so far is calculated to be unstable with respect to exchange striction in the experimentally observed upward arrow upward arrow downward arrow downward arrow antiferromagnetic structure for the Ising chain. The calculated inequivalence of the Co-Mn distances accounts for the ferroelectricity.

Correlation of structural, magnetic and transport properties with the tolerance factor in a low-doped La(0.875)Sr(0.125-x)Ca(x)MnO(3), (0 ≤x≤0.125) system: cross-over from Mott to Shklovskii-Efros variable range hopping conduction

Samples of the low-doped manganite La(0.875)Sr(0.125-x)Ca(x)MnO(3) (0≤x≤0.125) have been synthesized and the effect on the structural, magnetic and transport properties of decreasing the tolerance factor by replacing larger Sr(2+) ions with smaller Ca(2+) ions are reported. For samples with x≥0.0625, a concentration (x) dependent structural transition (rhombohedral ([Formula: see text]) to orthorhombic (Pnma)) has been detected at room temperature and the Curie temperature T(C) is found to decrease with increased Ca doping level. For samples with x≤0.0625, a narrow metallic region exists and the corresponding insulator to metal transition temperature T(MI) decreases with increasing Ca content, i.e. decreasing tolerance factor. In the paramagnetic region, x dependent crossover from Mott variable range hopping (Mott-VRH) to Shklovskii-Efros variable range hopping (SE-VRH) occurs as the Ca content increases. The thermoelectric power (TEP) of the samples increases substantially, varying inversely with the tolerance factor. These results are analysed from the consideration of increased bending of the Mn-O-Mn bond with the decrease of the average ionic radius of the A-site element [Formula: see text] and the tolerance factor t, which causes narrowing of the bandwidth, decrease of mobility of e(g) electrons and weakening of the double exchange (DE) interaction associated with the substitution of Ca.

Electronic correlations in CoO2, the parent compound of triangular cobaltates

A 59Co NMR study of CoO2, the x=0 end member of AxCoO2 (A=Na,Li,...) cobaltates, reveals a metallic ground state, though with clear signs of strong electron correlations: low-energy spin fluctuations develop at wave vectors q not equal to 0 and a crossover to a Fermi-liquid regime occurs below a characteristic temperature T* approximately 7 K. Despite some uncertainty over the exact cobalt oxidation state in this material, the results show that electronic correlations are revealed as x is reduced below 0.3. The data are consistent with NaxCoO2 being close to the Mott transition in the x-->0 limit.

Scaling behavior in thermoelectric misfit cobalt oxides

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.

Re-entrant metallicity and magnetoresistance induced by Ce for Sr substitution in SrCoO(3-δ)

Cerium for strontium substitution allows an oxygen deficient perovskite Sr(1-x)Ce(x)CoO(3-δ) to be stabilized with a cerium solubility limited to x≤0.15 (Trofimenko et al 1997 Solid State Ion. 100 183). For these samples, the magnetic properties depend clearly upon the oxygen content: Sr(0.9)Ce(0.1)CoO(2.74) and Sr(0.9)Ce(0.1)CoO(2.83) are weak and strong ferromagnets (T(C) = 160 K), respectively, the maximum ac-magnetic susceptibility of the latter being larger by two orders of magnitude than that of the former. In contrast to other Sr(1-x)L(x)CoO(3-δ) series (L =  lanthanide, Y(3) or Th(4+)), the electrical resistivity (ρ) behaviour does not simply reflect the magnetic behaviour. For x = 0.10 the re-entrant ρ feature becomes more pronounced whereas the ferromagnetic fraction and cobalt oxidation state increase. This unexpected behaviour could be related to the Ce(3+)/Ce(4+) mixed valency, the 4f localized moment of the Ce(3+) cations interacting with the conduction electrons through a Kondo-like mechanism. It is also found that the increase of oxygen vacancies favours the appearance of magnetoresistance at low T, reaching -50% at 5 K in 7 T for the Sr(0.95)Ce(0.05)CoO(2.61) sample prepared in a sealed tube.