Adiabatic charge pumping through a dot at the junction of N quantum wires

We study adiabatic charge pumping through a quantum dot placed at the junction of $N$ quantum wires. We explicitly map out the pattern of pumped charge as a function of the time-varying tunneling parameters coupling the wires to the dot and the phase between any two time varying parameters controlling the shape of the dot. We find that with $N-2$ time-independent well-coupled leads, the maximum pumped charge in the remaining two leads is strongly suppressed with increasing $N$, leading to the possibility of tuning of the pumped charge, by modulating the coupling of the $N-2$ leads.Comment: 5 pages, 6 figures, version to be published in PR

Measurement of probe displacement to the thermal resolution limit in photonic force microscopy using a miniature quadrant photodetector

A photonic force microscope comprises of an optically trapped micro-probe and a position detection system to track the motion of the probe. Signal collection for motion detection is often carried out using the backscattered light off the probe - however, this mode has problems of low S/N due to the small back-scattering cross-sections of the micro-probes typically used. The position sensors often used in these cases are quadrant photodetectors. To ensure maximum sensitivity of such detectors, it would help if the detector size matched with the detection beam radius after the condenser lens (which for backscattered detection would be the trapping objective itself). To suit this condition, we have used a miniature displacement sensor whose dimensions makes it ideal to work with 1:1 images of micron-sized trapped probes in the back-scattering detection mode. The detector is based on the quadrant photo-IC in the optical pick-up head of a compact disc player. Using this detector, we measured absolute displacements of an optically trapped 1.1 um probe with a resolution of ~10 nm for a bandwidth of 10 Hz at 95% significance without any sample or laser stabilization. We characterized our optical trap for different sized probes by measuring the power spectrum for each probe to 1% accuracy, and found that for 1.1 um diameter probes, the noise in our position measurement matched the thermal resolution limit for averaging times up to 10 ms. We also achieved a linear response range of around 385 nm with crosstalk between axes ~4% for 1.1 um diameter probes. The detector has extremely high bandwidth (few MHz) and low optical power threshold - other factors that can lead to it's widespread use in photonic force microscopy.Comment: 11 pages, 11 figure

Ringo: Interactive Graph Analytics on Big-Memory Machines

We present Ringo, a system for analysis of large graphs. Graphs provide a way to represent and analyze systems of interacting objects (people, proteins, webpages) with edges between the objects denoting interactions (friendships, physical interactions, links). Mining graphs provides valuable insights about individual objects as well as the relationships among them. In building Ringo, we take advantage of the fact that machines with large memory and many cores are widely available and also relatively affordable. This allows us to build an easy-to-use interactive high-performance graph analytics system. Graphs also need to be built from input data, which often resides in the form of relational tables. Thus, Ringo provides rich functionality for manipulating raw input data tables into various kinds of graphs. Furthermore, Ringo also provides over 200 graph analytics functions that can then be applied to constructed graphs. We show that a single big-memory machine provides a very attractive platform for performing analytics on all but the largest graphs as it offers excellent performance and ease of use as compared to alternative approaches. With Ringo, we also demonstrate how to integrate graph analytics with an iterative process of trial-and-error data exploration and rapid experimentation, common in data mining workloads.Comment: 6 pages, 2 figure

Ultra-Low-Power Embedded SRAM Design for Battery- Operated and Energy-Harvested IoT Applications

Internet of Things (IoT) devices such as wearable health monitors, augmented reality goggles, home automation, smart appliances, etc. are a trending topic of research. Various IoT products are thriving in the current electronics market. The IoT application needs such as portability, form factor, weight, etc. dictate the features of such devices. Small, portable, and lightweight IoT devices limit the usage of the primary energy source to a smaller rechargeable or non-rechargeable battery. As battery life and replacement time are critical issues in battery-operated or partially energy-harvested IoT devices, ultra-low-power (ULP) system on chips (SoC) are becoming a widespread solution of chip makers’ choice. Such ULP SoC requires both logic and the embedded static random access memory (SRAM) in the processor to operate at very low supply voltages. With technology scaling for bulk and FinFET devices, logic has demonstrated to operate at low minimum operating voltages (VMIN). However, due to process and temperature variation, SRAMs have higher VMIN in scaled processes that become a huge problem in designing ULP SoC cores. This chapter discusses the latest published circuits and architecture techniques to minimize the SRAM VMIN for scaled bulk and FinFET technologies and improve battery life for ULP IoT applications

Probing the dynamics of an optically trapped particle by phase sensitive back focal plane interferometry

The dynamics of an optically trapped particle are often determined by measuring intensity shifts of the back-scattered light from the particle using position sensitive detectors. We present a technique which measures the phase of the back-scattered light using balanced detection in an external Mach-Zender interferometer scheme where we separate out and beat the scattered light from the bead and that from the top surface of our trapping chamber. The technique has improved axial motion resolution over intensity-based detection, and can also be used to measure lateral motion of the trapped particle. In addition, we are able to track the Brownian motion of trapped 1 and 3 $\mu$m diameter beads from the phase jitter and show that, similar to intensity-based measurements, phase measurements can also be used to simultaneously determine displacements of the trapped bead as well as the spring constant of the trap. For lateral displacements, we have matched our experimental results with a simulation of the overall phase contour of the back-scattered light for lateral displacements by using plane wave decomposition in conjunction with Mie scattering theory. The position resolution is limited by path drifts of the interferometer which we have presently reduced to obtain a displacement resolution of around 2 nm for 1.1 $\mu$m diameter probes by locking the interferometer to a frequency stabilized diode laser.Comment: 10 pages, 7 figure

Detecting receiver attacks in VRTI-based device free localization

pre-printVariance-based Radio Tomographic Imaging (VRTI) is an emerging technology that locates moving objects in areas surrounded by simple and inexpensive wireless sensor nodes. VRTI uses human motion induced variation in RSS and spatial correlation between link variations to locate and track people. An artificially induced power variations in the deployed network by an adversary can introduce unprecedented errors in localization process of VRTI and, given the critical applications of VRTI, can potentially lead to serious consequences including loss of human lives. In this paper, we tackle the problem of detecting malicious receivers that report false RSS values to induce artificial power variations in a VRTI system. We use the term "Receiver Attack" to refer to such malicious power changes. We use a combination of statistical hypothesis testing and heuristics to develop real-time methods to detect receiver attack in a VRTI system. Our results show that we can detect receiver attacks of reasonable intensity and identify the source(s) of malicious activity with very high accuracy

Violating privacy through walls by passive monitoring of radio windows

pre-printWe investigate the ability of an attacker to passively use an otherwise secure wireless network to detect moving people through walls. We call this attack on privacy of people a "monitoring radio windows" (MRW) attack. We design and implement the MRW attack methodology to reliably detect when a person crosses the link lines between the legitimate transmitters and the attack receivers, by using physical layer measurements. We also develop a method to estimate the direction of movement of a person from the sequence of link lines crossed during a short time interval. Additionally, we describe how an attacker may estimate any artificial changes in transmit power (used as a countermeasure), compensate for these power changes using measurements from sufficient number of links, and still detect line crossings. We implement our methodology on WiFi and ZigBee nodes and experimentally evaluate the MRW attack by passively monitoring human movements through external walls in two real-world settings. We find that achieve close to 100% accuracy in detecting line crossings and determining direction of motion, even through reinforced concrete walls

Optimal Patent Licensing—Two or Three-Part Tariff

We look into technology transfer by an insider patentee in a spatial duopoly model under three types of licensing contracts—(i) two-part tariff with fixed fee and per-unit royalty, (ii) two-part tariff with fixed fee and ad-valorem royalty and (iii) general three-part tariff with fixed fee, per-unit and ad-valorem royalties. Under two-part tariff contracts, the licenser is better off with the per-unit royalty contract but the general contract does better than the other contracts. In contrast to the existing literature, all three licensing contracts may make the consumers worse-off compared to no licensing, with the lowest consumer surplus achieved under the general licensing contract. Welfare under the general licensing contract is equal to the welfare under two-part tariff with ad-valorem royalty and it is higher than the welfare under no licensing but lower than the welfare under two-part tariff with per-unit royalty. Hence, the general three-part licensing contract is privately optimal but not socially optimal. Similar conclusions hold also under a nonspatial linear demand model with differentiated products