Diamond Surface Functionalization via Visible Light-Driven C-H Activation for Nanoscale Quantum Sensing

Nitrogen-vacancy centers in diamond are a promising platform for nanoscale nuclear magnetic resonance sensing. Despite significant progress towards using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. NV molecular sensing requires that target molecules are immobilized within a few nanometers of NV centers with long spin coherence time. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be more readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown to be compatible with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C-H bonds on single-crystal diamond surfaces under ambient conditions using visible light. This functionalization method is compatible with charge stable NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof of principle, we use shallow ensembles of NV centers to detect nuclear spins from functional groups attached to the surface. Our approach to surface functionalization based on visible light-driven C-H bond activation opens the door to deploying NV centers as a broad tool for chemical sensing and single-molecule spectroscopy

Service differentiation in Wireless Local Area Networks

Wireless Local Area Networks (WLANs) have significantly developed as a means to provide Internet access at many places. There are different types of Internet traffic over WLANs such as data and voice, with different Quality of Service (QoS) requirements. This raises the need for the provision of service differentiation in WLANs. The traditional approach prioritizes voice over data, which gives an incentive for data applications to mark themselves as voice to gain higher QoS. This may lead to the degradation of the whole network and hence worsen QoS perceived by end users. In contrast, the service differentiation scheme proposed in my thesis provides different but equal services for different traffic types, which can eliminate the incentive mentioned above and has simple implementation

Journal of physiotherapy

Abstract—Wireless local area networks (WLANs) support a wide range of applications, with various packet sizes. This diversity is set to increase in 802.11e WLANs which effectively allow very large packets controlled by a transmission opportunity (TxOP) parameter. This paper demonstrates a new phenomenon which occurs as a result of this diversity: When a network carries some large packets and many small packets, the collision probability after a large packet is much larger than predicted by previous models. This can be important because collision probability determines the number of packet transmissions, and hence the energy consumption. We propose a candidate model which captures this effect. I

Performance analysis of IEEE 802.11 WLANs with saturated and unsaturated sources

This paper proposes a comprehensive but tractable model of IEEE 802.11 carrying traffic from a mixture of saturated and unsaturated (Poisson) sources, with potentially different quality-of-service (QoS) parameters, i.e., TXOP limit, CWmin, and CWmax. The model is used to investigate the interaction between these two types of sources, which is particularly useful for systems seeking to achieve load-independent 'fair' service differentiation. We show that, when the TXOP limit for unsaturated sources is greater than one packet, batches are distributed as a geometric random variable clipped to TXOP limit. Furthermore, we present asymptotic results for access delay distribution, which indicates that it is infeasible to obtain real-time service in the presence of eight or more saturated sources, regardless of the real-time traffic load, given that all stations use a CWmin of 32

Service differentiation without prioritization in IEEE 802.11 WLANs

Wireless LANs carry a mixture of traffic, with different delay and throughput requirements. The usual way to provide low-delay services is to give priority to such traffic. However this creates an incentive for throughput sensitive traffic also to use this service, which degrades overall network performance. We show, analytically and by simulation, that the performance of both delay and throughput sensitive traffic can be improved by scaling IEEE 802.11's CWmin and TXOP limit parameters in equal proportion. This reduces, but does not eliminate, the incentive for bulk data users to use the low-delay service. We further show that this incentive can be removed, while still giving improved performance to both classes, by reducing the CWmin of the high throughput class by a constant that is independent of the traffic load

Service differentiation without prioritization in IEEE 802.11 WLANs

Wireless LANs carry a mixture of traffic, with different delay and throughput requirements. The usual way to provide low-delay services is to give priority to such traffic. However this creates an incentive for throughput sensitive traffic also to use this service, which degrades overall network performance. We propose to allow applications to trade off delay for throughput, without giving preference to one class over another, by simultaneously scaling IEEE 802.11's CWmin and TXOP limit parameters. We provide a model of this scheme with two traffic classes, and show that increasing CWmin and TXOP limit in equal proportion reduces, but does not eliminate, the incentive for bulk data users to use the low-delay service. We show that subtracting a small constant from CWmin eliminates this incentive, while still giving improved performance to both classes

Performance analysis of IEEE 802.11 WLANs with saturated and unsaturated sources

This paper proposes a comprehensive but tractable model of IEEE 802.11 carrying traffic from a mixture of saturated and unsaturated (Poisson) sources, with potentially different QoS parameters, TXOP limit, CWmin and CWmax. The model is used to investigate the interaction between these two types of sources, which is particularly useful for systems seeking to achieve loadindependent ''fair'' service differentiation. We show that, when the TXOP limit for unsaturated sources is greater than one packet, batches are distributed as a geometric random variable clipped to TXOP limit. Furthermore, we present asymptotic results for the access delay distribution, which indicates that it is infeasible to obtain real-time service in the presence of 8 or more saturated sources regardless of the real time traffic load given that all stations use CWmin of 32