Optimization of sample-chip design for stub-matched radio-frequency reflectometry measurements

A radio-frequency (rf) matching circuit with an in situ tunable varactor diode used for rf reflectometry measurements in semiconductor nanostructures is investigated and used to optimize the sample-specific chip design. The samples are integrated in a 2-4 GHz stub-matching circuit consisting of a waveguide stub shunted to the terminated coplanar waveguide. Several quantum point contacts fabricated on a GaAs/AlGaAs heterostructure with different chip designs are compared. We show that the change of the reflection coefficient for a fixed change in the quantum point contact conductance can be enhanced by a factor of 3 compared to conventional designs by a suitable electrode geometry

Electrolyte gate dependent high-frequency measurement of graphene field-effect transistor for sensing applications

We performed radiofrequency (RF) reflectometry measurements at 2.4 GHz on electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable stub-matching circuit for impedance matching. We demonstrate that the gate voltage dependent RF resistivity of graphene can be deduced even in the presence of the electrolyte which is in direct contact with the graphene layer. The RF resistivity is found to be consistent with its DC counterpart in the full gate voltage range. Furthermore, in order to access the potential of high-frequency sensing for applications, we demonstrate time-dependent gating in solution with nanosecond time resolution.Comment: 14 pages, 4 figure

Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime

In situ tunable radio-frequency charge detection is used for the determination of the tunneling rates into and out of a graphene single quantum dot connected to only one lead. An analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations.Comment: 4 pages, 3 figure

The Normative Agency of Regional Organizations and Non‐governmental Organizations in International Peace Mediation

This article analyzes the increasingly prominent role of regional organizations (ROs) and non‐governmental organizations (NGOs) in promoting norms in mediation processes. In particular, we seek to understand the processes by which RO and NGO mediators promote the inclusivity norm to negotiating parties and the outcomes that result. We employ the concepts of local agency and social practices in examining the normative agency of ROs and NGOs in promoting and redefining the inclusivity norm. Through illustrative case studies of peace processes in South Sudan and Myanmar, we argue that ROs’ and NGOs’ mediation practices reflect their claims to alternative resources of power, such as long‐standing expertise and insider status in the context, and build congruence with strong local norms. We provide nuanced theoretical insights on RO and NGO mediators’ claims to agency and provide empirical illustrations on how these claims contribute to constitutive changes to norms

UN Peacekeeping at 75: Achievements, Challenges, and Prospects

This year marks the 75th anniversary of what the UN itself understands to be its first peacekeeping operation. It is therefore an appropriate time to reflect on the track record of UN peacekeeping in its efforts to try to maintain and realize peace and security. Moreover, this milestone invites us to ponder what lies ahead in the realm of peacekeeping. For this reason, this forum article brings together both academics and UN officials to assess the achievements and challenges of UN peacekeeping over the past 75 years. Through a dialogue among peacekeeping scholars and practitioners, we hope to identify current trends and developments in UN peacekeeping, as well as explore priorities for the future to improve the effectiveness of peacekeeping operations in terms of achieving their mandate objectives, such as maintaining peace, protecting civilians, promoting human rights, and facilitating reconciliation. This forum article is structured into six thematic sections, each shedding light on various aspects of UN peacekeeping: (1) foundational principles of UN peacekeeping - namely, consent, impartiality, and the (non-)use of force; (2) protection of civilians; (3) the primacy of politics; (4) early warning; (5) cooperation with regional organizations; and (6) the changing geopolitical landscape in which UN peacekeeping operates

Neutral states as peace mediators: favoured or restrained by norms?

Neutral states have traditionally been seen as particularly well suited to function as international mediators. This assessment was based on the fact that both concepts - neutrality and mediation - have their roots in attempts to contain violent conflicts and thereby combine realist and idealistic dimensions of international relations. While due to these normative commonalities the increased influence of norms in mediation might be deemed to favour the role of neutral states as mediators, a more nuanced analysis reveals a mixed impact: The new norms made mediation enter into policy fields to which neutrality does not apply. But they also increased the complexities of mediation processes which in turn could open up new opportunities for neutral states