Combining conventional tree-ring measurements with wood anatomy and strontium isotope analyses enables dendroprovenancing at the local scale.

Dendroprovenancing provides critical information regarding the origin of wood, allowing further insights into economic exploitation strategies and source regions of timber products. Traditionally, dendroprovenancing relies on pattern-matching of tree rings, but its spatial resolution is limited by the geographical coverage of species-specific chronologies available for crossdating and, in the case of short-distance trades, by scarce environmental variability. Here, we present an approach to provenance timber with high spatial resolution from forested areas that have been exploited intensively throughout history, with the aim to understand the sustainability of the various woodland management practices used to supply timber products. To this end, we combined tree-ring width (TRW), wood anatomical and geochemical analyses in addition to multivariate statistical validation procedures to trace the origin of living oak trees (Quercus robur) sampled in four stands located within a 30-km radius around the city of Limoges (Haute-Vienne, France). We demonstrate that TRW and wood anatomical variables (and in particular cell density) robustly discriminate the eastern from the western site, while failing to trace the origin of trees from the northern and southern sites. Here, strontium isotopic ratios (87Sr/86Sr) and Ca concentrations identify clusters of trees which could not be identified with TRW or wood anatomy. Ultimately, our study demonstrates that the coupling of wood anatomy with geochemical signatures allows to correctly pinpoint the origin of trees. Given the small geographic scale of our study and the limited differences in elevation and climate between study sites, our results are particularly promising for future dendroprovenancing studies. We thus conclude that the combination of multiple approaches will not only increase the accuracy of dendroprovenancing studies at local scales, but could also be implemented at much larger scales to identify trends in historic timber supply throughout Europe.

Growth of long and aligned multi-walled carbon nanotubes on carbon and metal substrates.

Well aligned, long and dense multi-walled carbon nanotubes (CNT) can be grown on both carbon fibres and any metal substrates compatible with the CNT synthesis temperature. The injection-CVD process developed involves two stages, including fibre pretreatment by depositing a SiO(2)-based sub-layer from an organometallic precursor followed by CNT growth from toluene/ferrocene precursor mixture. Carbon substrates, as well as metals, can easily be treated with this process, which takes place in the same reactor and does not need any handling in between the two stages. The aligned CNT carpets obtained are similar to the ones grown on reference quartz substrates. The CNT growth rate is fairly high (ca. 30 µm min(-1)) and it is possible to control CNT length by varying the CNT synthesis duration. The thickness of the SiO(2)-based sub-layer can be varied and is shown to have an influence on the CNT growth. This layer is assumed to play a diffusion barrier layer role between the substrate and the iron based catalyst nanoparticles producing CNT. The CNT anchorage to the carbon fibres has been checked and good overall adhesion proved, which is in favour of a good transfer of electrical charge and heat between the nanotubes and fibre.

How can a climate change perspective be integrated into public health surveillance?

OBJECTIVES: Climate change may be considered as a key factor for environmental change, exposure to health risks and pathogens, consequently impairing the state of health among populations. Efficient health surveillance systems are required to support adaptation to climate change. However, despite a growing awareness, the public health surveillance sector has had very little involvement in the drafting of adaptation plans. This paper proposes a method to raise awareness about climate change in the public health community, to identify possible health risks and to assess the needs for reinforced health surveillance systems. METHODS: A working group was set up comprising surveillance experts in the following fields: environmental health; chronic diseases and; infectious diseases. Their goal was to define common objectives, to propose a framework for risk analysis, and to apply it to relevant health risks in France. RESULTS: The framework created helped to organize available information on climate-sensitive health risks, making a distinction between three main determinants as follows: (1) environment; (2) individual and social behaviours; and (3) demography and health status. The process is illustrated using two examples: heatwaves and airborne allergens. CONCLUSION: Health surveillance systems can be used to trigger early warning systems, to create databases which improve scientific knowledge about the health impacts of climate change, to identify and prioritize needs for intervention and adaptation measures, and to evaluate these measures. Adaptation requires public health professionals to consider climate change as a concrete input parameter in their studies and to create partnerships with professionals from other disciplines.

[Estimation of prevalence of depressive episodes in French adolescents]. / Estimation de la prévalence de l'épisode dépressif chez l'adolescent en France.

BACKGROUND: Although the diagnosis and treatment of depressive disorders are important public health issues in adolescents, epidemiological data in this population are scarce. OBJECTIVE: The aims of this study were to estimate the 12-month prevalence rates of depressive disorders among ninth grade pupils in French schools, and to identify the sociodemographic correlates. METHODS: The data were collected through a national cross-sectional study conducted among ninth grade pupils in France in 2003-2004. Depressive disorders were assessed using a self-administered questionnaire derived from the standardised Composite International Diagnosis Interview-Short Form (CIDI-SF). RESULTS: A total of 7110 teenagers (mean age 15.1 years) were included. Of these, 9.6% (95% CI 8.6-10.6) reported symptoms corresponding to at least one major depressive episode (MDE) over the past 12 months. Three correlates were independently associated with a higher prevalence of 12-month MDE: being a female (adjusted odds ratio 3.0; 95% CI 2.4-3.8), being greater or equal to 16 years old (aOR=2.2; 95% CI 1.0-5.0) and living alone with one's mother (aOR=1.7; 95% CI 1.3-2.4) or with one's mother and her spouse (aORa=1.4; 95% CI 1.0-2.1). CONCLUSION: The high prevalence of depressive disorders in French adolescents is thoroughly discussed. The needs for developing mental health surveillance, comprehensive prevention and care programs for this population are crucial.

[Reporting and interviewing delays in contact investigation of tuberculosis, Seine-Saint-Denis, from April to June 2008]. / Délais de signalement et d'entretien dans l'enquête autour d'un cas de tuberculose, Seine-Saint-Denis, avril-juin 2008.

BACKGROUND: In France, one of the main components of the tuberculosis control program is contact investigation around all tuberculosis cases. For this purpose, all cases of tuberculosis are to be reported to the health authorities (Centre de lutte antituberculeuse) within 48 hours of diagnosis. The Centre then conducts an initial patient interview within three days of the report in order to establish a list of contacts requiring evaluation. Given that a delay in action may play a role in the continued disease transmission, it appeared necessary to study more precisely this subject in a French area with a high annual new case rate, the Seine-Saint-Denis. METHODS: A descriptive and retrospective study included all tuberculosis cases reported and received between April and June 2008. The two periods were statistically analyzed with socio-demographic, clinical-biological and investigations data. RESULTS: For the 148 cases reported during this period, a first interview was required for 123. The average time period between initiation of anti-tuberculosis therapy and reception of the report was 11.08 days. The overly long delay could be explained in part by the inappropriate use of the notification form (45.5%) designed for non-urgent collection of epidemiological data, and in part by the underuse of telephone reporting (8.1%). The first interview was not performed for 19 cases and the average time between reception of the notification and the patient interview was 6.58 days. Having the patient's phone number appeared essential to meet the deadline (odds ratio: 5.3; 95% confidence interval [1.7-16.9]). Few interviews were made in person. Shortage in financial and human resources and the delayed case reporting could be part of the explanations. Deadlines were met much better for cases of pleuro-pulmonary tuberculosis compared with other localizations, for reporting (39.2% versus 13.5%, p<0.01) and for the first interview (48.8% versus 28.6%, p=0.03). CONCLUSION: This study reports some risk factors associated with delayed action and highlights the need for improved reporting of tuberculosis cases and contact investigations.

Monolithic integration of a 10 µm cut-off wavelength InAs/GaSb type-II superlattice diode on GaAs platform.

At room temperature, a 10 µm cut-off wavelength coincides with an infrared spectral window and the peak emission of blackbody objects. We report a 10 µm cut-off wavelength InAs/GaSb T2SL p-i-n diode on a GaAs substrate with an intentional interfacial misfit (IMF) array between the GaSb buffer layer and GaAs substrate. Transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed that the heterostructure on GaSb-on-GaAs is epitaxial, single-crystalline but with a reduced material homogeneity, extended lattice defects and atomic segregation/intermixing in comparison to that on the GaSb substrate. Strain-induced degradation of the material quality is observed by temperature-dependent current-voltage measurements. The T2SL with the IMF array appears as a potentially effective route to mitigate the impact of the lattice mismatch once its fabrication is fully optimized for these systems, but additional strain compensating measures can enable a low cost, scalable manufacturing of focal plane arrays (FPA) for thermal imaging cameras for spectroscopy, dynamic scene projection, thermometry, and remote gas sensing.

[Prevalence of asthma among adults in France, data from the Constances cohort study]. / Prévalence de l'asthme chez l'adulte en France, données de la cohorte Constances.

INTRODUCTION: The objectives of our study were to estimate the prevalence of asthma in adults in France and to study the effects of gender on the associations of asthma with the corpulence and socio-economic characteristics of individuals. METHODS: We estimated the prevalence of current asthma (asthma attack in the past 12 months or current treatment for asthma) from data collected at inclusion in the Constances cohort study in 2013-2014. Analyses were performed separately in men and women, using robust Poisson regression for multivariate analysis. RESULTS: Using data from 34,100 participants in the cohort (men: 47.7 %; mean age: 44.6 years), the prevalence of current asthma was estimated to be 5.8 % (5.1 % in men, 6.4 % in women). The risk of asthma was increased in women with high body mass index (BMI) or waist circumference. In men, only a high waist circumference was associated with an increased risk of asthma. An association with low socioeconomic status was observed only among women. CONCLUSION: The associations of asthma with corpulence and socioeconomic status differed between men and women. Additional analyses should provide a better understanding of the mechanisms responsible for these differences.

[Implementation of the dematerialization of the patient file in the context of COVID in the ONCORAD radiotherapy units: Transition to "paperless"]. / Mise en place de la dématérialisation du dossier patient dans un contexte de COVID dans les services de radiothérapie de l'ONCORAD : passage « au sans papier ¼.

Paper patient file sharing has clearly been identified as a risk behavior for the COVID-19 virus transmission in radiotherapy units. In order to overcome this, the ONCORAD radiotherapy units worked on total dematerialization of the paper patient file, within 3 weeks. The methodology is based on a quality approch. This work has led to a convincing improvement in the management of risks a priori and a smoother patient care workflow.

TB outcomes and mortality risk factors in adult migrants at the Thailand-Myanmar border.

BACKGROUND: Cross-border migrants at the Thailand-Myanmar border are an underserved and vulnerable population. We aimed to identify the causes and risk factors for TB mortality at a migrant-friendly TB programme.METHODS: Routinely collected data on TB cases, treatment outcomes and causes of death were analysed for adult TB cases diagnosed between January 2013 and April 2017. Mortality in the 6 months post-diagnosis was calculated and risk factors were identified using multivariable Poisson regression.RESULTS: Of the 1344 TB cases diagnosed, 1005 started treatment and 128 died. Case fatality rate was 9.5% and the TB mortality rate was 2.4/100 person-months. The number of pre-treatment deaths (33/128) and losses to follow-up (9.0%) were high. Among cases enrolled in treatment, the treatment success rate was 79.8%. When stratified by HIV status, case fatality was higher in HIV-positive cases not on antiretroviral therapy (ART) (90.3%) or with unknown HIV status (31.8%) than those on ART (14.3%) or HIV-negative (8.6%).CONCLUSION: This TB programme achieved high treatment success rates in a population with a substantial burden of TB-HIV coinfection. Expanding access to HIV testing and ART is crucial to reduce mortality. Striving towards same-day TB diagnosis and treatment could reduce death and loss to follow-up.

[Readmissions to hospital for asthma in France, 2002-2005]. / Les réadmissions pour asthme en France, 2002-2005.

BACKGROUND: Most hospital admissions with asthma are avoidable. The objective of the analysis was to describe hospital readmissions for asthma. METHODS: Using data from the French hospital information system, admissions for asthma or for acute respiratory failure associated with asthma that occurred in 2-44 years-old patients between 2002 and 2005 in France (excluding French overseas departments) were analysed. Readmission rates at 7 days and at 1 year were estimated using the Kaplan-Meier method. RESULTS: The risk of readmission at 1 year was 15.0%. It varied according to age (higher in 2-4 year and 35-44 years-old patients) and sex (higher in 10-34 years-old females) and increased with the length of stay of the index admission. The risk of readmission at 7 days was 1.1% and was higher for the shortest lengths of stay. CONCLUSION: Readmissions for asthma are pertinent indicators for the monitoring of asthma, especially the clinical management of the disease. Using data from an increasing number of years, together with linkage of hospital admissions and asthma drug reimbursement data, should allow a better understanding of severe asthma in France.

[Chronic bronchitis: prevalence and quality of life. Analysis of data from the French Health Interview Survey 2002-2003]. / Bronchite chronique: prévalence et qualité de vie.

INTRODUCTION: Chronic bronchitis is associated with an increased risk of COPD and health-related quality of life (HRQoL) impairment. The objectives of the study were to estimate the prevalence of chronic bronchitis and to describe its relations with quality of life. METHODS: The French Health Interview Survey was conducted in 2003 in a representative sample of households. Data were collected during an interviewer's visits to the home. Respiratory symptoms and HRQoL (SF-36) were assessed in 9,050 adults aged 45 years and older using a self-administered questionnaire. RESULTS: The prevalence of chronic bronchitis was estimated at 3.5%. Chronic bronchitis was associated with an impaired physical component summary score after adjusting for sex, age and dyspnoea. It was associated with a reduced mental component summary score (MCS) among men. In women, this association was only significant in the absence of dyspnoea. CONCLUSION: The prevalence of chronic bronchitis was 3.5% among adults aged 45 years and older. Chronic bronchitis was associated with impairment in health-related quality of life.

Factors controlling the variability of 137Cs concentrations in 5 coastal rivers around Fukushima Dai-ichi power plant.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to the contamination by radiocesium (137Cs) of large drained areas. Cesium-137 concentrations in rivers result from complex transfer processes, depending on multiple forcings. Better knowledge of the factors controlling these concentrations is therefore a prerequisite to improve predictions of 137Cs transfers within river catchments. This study aimed at analyzing the spatial and temporal variability of 137Cs concentrations in rivers and identifying the key factors controlling their variability. Published values of 137Cs concentrations in rivers in the north of FDNPP were collected, characterizing 122 sampling sites from May 2011 to October 2014. It resulted in three datasets: dissolved concentrations CW (Bq/L), concentrations in suspended sediment CSS (Bq/kg) and total concentrations CT (Bq/L). The resulting database reflected a large variety of catchments and hydrological conditions. Observed 137Cs concentrations varied by 2-4 orders of magnitude and were poorly explained (R2 = 0.13-0.38) by the average contamination density. Indices summarizing the complex spatial and temporal properties of the catchments were proposed as candidate explanatory variables of concentrations in rivers. They were selected by stepwise regression for each dataset (CW, CSS, CT). For the three datasets, the selection and combination of 5-10 indices significantly better explained this variability (R2 = 0.69-0.83). Deposit indices were identified as first drivers of concentrations in rivers. A deposit index was selected for each dataset, indicating no effect of the contamination distribution for CW, whereas CT and CSS required considering the distribution of contamination and connectivity, as well as the presence of dams for CSS. The others selected variables significantly contributed to explain the concentration variability. This meta-analysis emphasizes the importance of structural (e.g. slope, land-cover) and functional (e.g. delay, season, rainfall) properties in the dissimilarities of catchments responses, stressing that assessments could be improved by including more these properties in models.

[Risk factors of preeclampsia in single pregnancy]. / Facteurs de risque de la prééclampsie en cas de grossesse unique.

OBJECTIVES: Study of the clinical risk factors of preeclampsia during a single pregnancy. MATERIALS AND METHODS: Retrospective case-control study during five years. RESULTS: One hundred and eighty-eight cases of preeclampsia have been studied, with 147 called severe (78.2%). We find as risk factors: first pregnancy (OR=2.11; IC 95% [1.30-3.35]), primiparity (OR=2.67; IC 95% [1.67-4.29]), primipaternity (OR=3.55; IC 95% [2.13-5.83], maternal overweight (OR=2.50; IC 95% [1.55-4.05]), personal history of preeclampsia (OR=8.12; IC 95% [2.37-45.65]), personal history of hypertension (OR=2.77; IC 95% [1.01-7.99]), familial history of preeclampsia (OR=1.04; IC 95% [1.01-1.08]), familial history of hypertension at the first step (OR=2.61; IC 95% [1.32-5.47]). Two elements have been found as protected: tobacco before pregnancy (OR=0.51; IC 95% [0.36-0.85]), tobacco during pregnancy (OR=0.52; IC 95% [0.30-0.92]). CONCLUSION: Preeclampsia is responsible of a high maternal and fetal morbidity. The risk factors are widespread, the only use of them is not enough to determine the individual risk. A second step could be to determine if biological markers are better than clinical factors.

[Asthma and socioeconomic characteristics in France in 2012]. / Asthme et caractéristiques socioprofessionnelles en France en 2012.

INTRODUCTION: The prevalence of adult asthma is around 6-7% in France. This disease is multifactorial and is related in particular to occupational factors. Using data from The French Health, Health Care and Insurance Survey (ESPS), this study aimed to describe asthma prevalence in France according to socio-economic status in 2012. METHODS: This analysis included the population aged 15 years and over. Current asthma, defined by a declaration of having asthma in the last 12 months, was analyzed according to socio-economic variables available in the ESPS survey. RESULTS: Among the 23,047 subjects interviewed, 12,565 were included in the analysis. Current asthma frequency was 7.4%. Higher risk of asthma was observed in unemployed, non-qualified persons, with a lower income, or having free healthcare insurance. Regarding occupations, in men, trade and commerce employees, personal services employees and administrative employees were associated with a higher level of current asthma prevalence. CONCLUSIONS: These results show that subjects with lower socio-economic status are more likely to suffer from asthma. New epidemiological tools in France, including cohorts (Constances, COSET) will be helpful to study more precisely the associations between asthma and occupational factors.

[Trends in hospital admissions for asthma in France, 1998-2002]. / Evolution des hospitalisations pour asthme en France métropolitaine, 1998-2002.

BACKGROUND: As the quality of asthma care influences hospital admission rates, we described hospitalizations for asthma and studied trends in admission rates in France from 1998 to 2002. METHODS: Using data from the French hospital information system, admissions for asthma were defined by the J45 or J46 codes (ICD-10) as primary diagnosis, and admissions for acute respiratory failure (ARF) associated with asthma by the J96.0 code as primary diagnosis and the J45 or J46 codes as an associated diagnosis. Annual rates of admission adjusted for age and sex were calculated. RESULTS: During the study period, the adjusted asthma admission rate decreased by 5% per year (from 10.8/10,000 in 1998 to 8.6/10,000 in 2002). A significant decrease was observed in children aged 10-14 years (-5%/year) and in older people (from -7%/year in 15-19 years old to -9%/year in people aged 50 years or more), whereas no significant decrease was seen in youngest children (-2%/year in children aged 0-1 or 5-9 years, +0.1%/year in those aged 2-4 years). Although not statistically significant, an increase in admission rate for ARF associated with asthma was observed (+5%/year). CONCLUSION: Admission rates for asthma decreased between 1998 and 2002 in people aged 10 years and older. However, changes in coding practices or admission policies cannot be excluded and the extent to which the observed trends reflect changes in preventive care among patients with asthma remains to be assessed.

Prognostic factors after hospitalization for COPD exacerbation.

INTRODUCTION: Hospitalizations for acute exacerbation of chronic obstructive pulmonary disease (AECOPD) are increasing in France. AECOPD are associated with impaired health status and increased health care costs. METHODS: Using data from the French national health insurance information system, we studied mortality, readmissions and lung function testing after discharge among adults hospitalized for AECOPD in 2013. RESULTS: The cumulative probabilities of death and readmission for EACOPD were 21% and 31% respectively. The survival was better among women, even after taking into account the other risk factors (age, previous hospitalization for AECOPD, comorbidities, exacerbation severity). In multivariate analysis, the risk of readmission was increased among men and people living in socially disadvantaged areas. A lung function testing was performed in 34% within 3 months after discharge. Female gender, advanced age, comorbidities and living in a disadvantaged area were associated with a lower frequency of lung function testing. CONCLUSIONS: Women had a better prognosis than men after AECOPD hospitalization. The frequency of lung function testing after discharge remained low, particularly among women and people living in disadvantaged areas.

Improving transfer functions to describe radiocesium wash-off fluxes for the Niida River by a Bayesian approach.

This paper proposed methodological refinements of the generic transfer function approach to reconstruct radiocesium wash-off fluxes from contaminated catchments, by the integration of hydrological descriptors (passed volume of water, flow rate fluctuations and antecedent flow conditions). The approach was applied to the Niida River (Fukushima prefecture, Japan) for the period 03/2011-03/2015, for which daily flow rate (m3/s) and infrequent total radiocesium concentration (Bq/L) values were available from literature. Three models were defined, generic TF (Φ0), flow-corrected time variant (Φ1) and antecedent-flow corrected variant (Φ2). Calibration of these models' parameters was performed with a Bayesian approach because it is particularly adapted to limited datasets and censored information, and it provides parameters distributions. The model selection showed strong evidence of model Φ2 (indicated by marginal likelihood), which integrates current and recent hydrology in its formulation, and lower prediction errors (indicated by RMSE and ME). Models Φ1 and Φ2 better described wash-off dynamics compared to model Φ0, due to the inclusion of one or several hydrological descriptors. From March 2011 to March 2015, model Φ2 estimated 137Cs export from Niida catchment between 0.32 and 0.67 TBq, with a median value of 0.49 TBq, which represents around 0.27% of the initial fallout and could represent a significant source-term to the Ocean compared to the direct release from Fukushima Dai-ichi Nuclear Power Plant (FDNPP). Moreover the remaining 99% of the initial radiocesium fallout within the catchment may constitute a persistent contamination source for wash-off. Although the proposed methodology brought improvements in the assessment of wash-off fluxes, it remains an empirical interpolation method with a limited predictive power, particularly for recent low activities. To improve predictions, modelling approaches require more observed data (particularly more activity values corresponding to more hydrological conditions), and the inclusion of more hydrological descriptors.

[Increase in asthma prevalence among young children in France]. / Augmentation de la prévalence de l'asthme chez le jeune enfant en France.

INTRODUCTION: Few data on change over time of asthma prevalence in French children are available. METHODS: Data from the 2012-2013 national health survey of schoolchildren conducted in a random sample of almost 20,000 children in the last year of nursery school were compared to those which had been collected in 2005-2006 in the same grade level using the same methodology. RESULTS: In the 2012-2013 survey, children had a lifetime prevalence of asthma of 11.0% with 11.8% reporting wheezing in the preceding year. Asthma was more frequent and more often uncontrolled in children from families with low socioeconomic status. Compared to the survey conducted in the same grade level in 2005-2006, the prevalence ratios adjusted for children's gender and obesity, family structure, parental unemployment and region were 1.13 [1.05-1.21] for lifetime asthma and 1.12 [1.05-1.17] for past-year wheezing. CONCLUSION: In France, the prevalence of asthma in young children increased between 2005 and 2012. The socioeconomic status of children's parents affects both asthma prevalence and control.

Migration histories of multidrug-resistant tuberculosis patients from the Thailand-Myanmar border, 2012-2014.

SETTING: Multidrug-resistant tuberculosis (MDR-TB) is a growing public health threat in South-East Asia. TB is typically a disease of poverty and can be spread by infectious humans who migrate from one region to another. DESIGN: We interviewed 20 MDR-TB patients on the Thailand-Myanmar border with regard to their migration histories. Migration origins and destinations were mapped. RESULTS: All but one participant had a history of migration, and maps of migration ranges revealed wide geographic dispersal. Most described living and work conditions that could contribute to the spread of drug-resistant TB, including numerous contacts and crowded living quarters. CONCLUSION: Our results show that at least some migrant workers in the region carry MDR-TB, and indicate that this subgroup of the population is important with regard to the transmission of MDR-TB throughout the region. Migrants in this region come into contact with high numbers of people and may be able to spread the disease across wide geographic ranges. Access to diagnosis and treatment and socio-economic development are at least as important as any TB control measures, meaning that innovative and bold approaches that extend across international borders are needed to address these problems.

Development of TEM and SEM high brightness electron guns using cold-field emission from a carbon nanotip.

A newly developed carbon cone nanotip (CCnT) has been used as field emission cathode both in low voltage SEM (30 kV) electron source and high voltage TEM (200 kV) electron source. The results clearly show, for both technologies, an unprecedented stability of the emission and the probe current with almost no decay during 1h, as well as a very small noise (rms less than 0.5%) compared to standard sources which use tungsten tips as emitting cathode. In addition, quantitative electric field mapping around the FE tip have been performed using in situ electron holography experiments during the emission of the new tip. These results show the advantage of the very high aspect ratio of the new CCnT which induces a strong enhancement of the electric field at the apex of the tip, leading to very small extraction voltage (some hundred of volts) for which the field emission will start. The combination of these experiments with emission current measurements has also allowed to extract an exit work function value of 4.8 eV.