Realization of a Tunable Artificial Atom at a Supercritically Charged Vacancy in Graphene

The remarkable electronic properties of graphene have fueled the vision of a graphene-based platform for lighter, faster and smarter electronics and computing applications. One of the challenges is to devise ways to tailor its electronic properties and to control its charge carriers. Here we show that a single atom vacancy in graphene can stably host a local charge and that this charge can be gradually built up by applying voltage pulses with the tip of a scanning tunneling microscope (STM). The response of the conduction electrons in graphene to the local charge is monitored with scanning tunneling and Landau level spectroscopy, and compared to numerical simulations. As the charge is increased, its interaction with the conduction electrons undergoes a transition into a supercritical regime 6-11 where itinerant electrons are trapped in a sequence of quasi-bound states which resemble an artificial atom. The quasi-bound electron states are detected by a strong enhancement of the density of states (DOS) within a disc centered on the vacancy site which is surrounded by halo of hole states. We further show that the quasi-bound states at the vacancy site are gate tunable and that the trapping mechanism can be turned on and off, providing a new mechanism to control and guide electrons in grapheneComment: 18 pages and 5 figures plus 14 pages and 15 figures of supplementary information. Nature Physics advance online publication, Feb 22 (2016

Utilization of maternal health care services in post-conflict Nepal

Tulsi Ram Bhandari, Prabhakaran Sankara Sarma, Vellappillil Raman Kutty Achutha Menon Centre for Health Science Studies, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India Background: Despite a decade-long armed conflict in Nepal, the country made progress in reducing maternal mortality and is on its way to achieve the Millennium Development Goal Five. This study aimed to assess the degree of the utilization of maternal health care services during and after the armed conflict in Nepal.Methods: This study is based on Nepal Demographic and Health Survey data 2006 and 2011. The units of analysis were women who had given birth to at least one child in the past 5 years preceding the survey. First, we compared the utilization of maternal health care services of 2006 with that of 2011. Second, we merged the two data sets and applied logistic regression to distinguish whether the utilization of maternal health care services had improved after the peace process 2006 was underway.Results: In 2011, 85% of the women sought antenatal care at least once. Skilled health workers for delivery care assisted 36.1% of the women, and 46% of the women attended postnatal care visit at least once. These figures were 70%, 18.7%, and 16%, respectively, in 2006. Similarly, women were more likely to utilize antenatal care at least once (odds ratio [OR] =2.18, confidence interval [CI] =1.95–2.43), skilled care at birth (OR =2.58, CI =2.36–2.81), and postnatal care at least once (OR =4.13, CI =3.75–4.50) in 2011.Conclusion: The utilization of maternal health care services tended to increase continuously during both the armed conflict and the post-conflict period in Nepal. However, the increasing proportion of the utilization was higher after the Comprehensive Peace Process Agreement 2006. Keywords: antenatal care, armed conflict, Nepal, post-conflict, postnatal care, skilled care at birt