Money as a mechanism in a Bewley economy

We study what features an economic environment might possess, such that it would be Pareto efficient for the exchange of goods in that environment to be conducted on spot markets where those goods trade for money. We prove a conjecture that is essentially due to Bewley [1980,1983]. Monetary spot trading is nearly efficient when there is only a single perishable good (or a composite commodity) at each date and state of the world; random shocks are idiosyncratic, privately observed, and temporary; markets are competitive; and the agents are very patient. This result is a fairly close analogue, for trade using outside, fiat money, of a recent characterization by Levine and Zame [2002] of environments in which spot trade using inside money, in the form of one-period debt payable in a commodity, is nearly Pareto efficient. We also study a example where expansionary monetary mechanism Pareto dominates laissez-faire or contractionary monetary mechanism in an environment with impatient agents.Money ; Monetary theory

Error suppression in Hamiltonian based quantum computation using energy penalties

We consider the use of quantum error detecting codes, together with energy penalties against leaving the codespace, as a method for suppressing environmentally induced errors in Hamiltonian based quantum computation. This method was introduced in [1] in the context of quantum adiabatic computation, but we consider it more generally. Specifically, we consider a computational Hamiltonian, which has been encoded using the logical qubits of a single-qubit error detecting code, coupled to an environment of qubits by interaction terms that act one-locally on the system. Energy penalty terms are added that penalize states outside of the codespace. We prove that in the limit of infinitely large penalties, one-local errors are completely suppressed, and we derive some bounds for the finite penalty case. Our proof technique involves exact integration of the Schrodinger equation, making no use of master equations or their assumptions. We perform long time numerical simulations on a small (one logical qubit) computational system coupled to an environment and the results suggest that the energy penalty method achieves even greater protection than our bounds indicate.Comment: 26 pages, 7 figure

Exploring the Relationship Between Exchange Rate Pass-Through and CPI Inflation in Mainland China and India

By examining the link between exchange rate transmission and cpi inflation across countries, we investigate whether there is a considerable link between the two. In this paper, we examine data for two representative Asian countries, mainland China and India, to determine whether there is a relationship between the two. The study finds no significant link between exchange rate and cpi inflation for China by comparing 40 years of data for these two countries, but for India, there is a particularly clear link. The difference between the two is mainly due to the different exchange rate control systems implemented by the two governments. The paper will explore and test this further to find if there is a link between the two and which factor has the greatest impact on the exchange rate

Optical Focusing and Imaging through Scattering Media

Optical techniques, which have been widely used in various fields including bio-medicine, remote sensing, astronomy, and industrial production, play an important role in modern life. Optical focusing and imaging, which correspond to the basic methods of utilizing light, are key to the implementation of optical techniques. In free space or a nearly transparent medium, optical imaging and focusing can be easily realized by using conventional optical elements, such as lenses and mirrors, due to the ballistic propagation of light in these media. However, in scattering media like biological tissue and fog, refractive index inhomogeneities cause diffusive propagation of light that increases with depth, which restricts the use of optical methods in thick, scattering media. Generally speaking, scattering media poses three challenges to optical focusing and imaging: wavefront aberrations, glare, and decorrelation. Wavefront aberrations can randomize light traveling through a scattering medium, disrupt the formation of focus, and break the conjugate relation in imaging. Glare caused by backscattering will largely impair the visibility of imaging, and decorrelation in dynamic media requires systems that counter the effect of scattering to operate faster than the decorrelation time. In this thesis, we explored solutions to the problem of scattering from different aspects. We presented Time Reversal by Analysis of Changing wavefronts from Kinetic targets (TRACK) technique to realize noninvasive optical focusing through a scattering medium. We showed that by taking the difference between time-varying scattering fields caused by a moving object and applying optical phase conjugation, light can be focused back to the location previously occupied by the object. To tackle the decorrelation of living tissue, we built up a fast digital optical phase conjugation (DOPC) system based on FPGA and DMD, which has a response time of 5.3 ms and was the fastest DOPC system in the world before 2017. We demonstrated that the system is fast enough to focus light through 2.3mm-thick living mouse skin. As for glare, inspired by noise canceling headphones, we invented an optical analogue termed coherence gated negation (CGN) technique. CGN can optically cancel out the glare in an active illumination imaging scenario to realize imaging through scattering media, like fog. In the experiment, we suppressed the glare by an order of magnitude and allowed improved imaging of a weak target. Finally, we demonstrated a method to image a moving target through scattering media noninvasively. Its principle roots are in the speckle-correlation-based imaging (SCI) invented by Ori Katz. We improved the technique and extended its application to bright field imaging of a moving target.</p

A sub-critical barrier thickness normally-off AlGaN/GaN MOS-HEMT

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al0.25Ga0.75N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO2) as the gate dielectric. They demonstrated threshold voltages (Vth) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (VGS) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices

Imaging moving targets through scattering media

Imaging in turbid media such as biological tissue is challenging primarily due to light scattering, which degrades resolution and limits the depths at which we can reliably image objects. There are two main approaches for realizing non-destructive optical imaging through scattering tissue: gated approaches, which serve to distinguish and reject the multiply scattered photons; and non-gated approaches, which detect both the unscattered and scattered light contributions, and leverage the information from the scattering process in order to image the object1. In terms of non-gated approaches, both wavefront shaping (WFS) and speckle-correlation-based imaging (SCI) techniques can achieve high-resolution imaging of objects hidden within scattering media1,2. WFS techniques exploit the principles of time-reversal to undo the effects of scattering, whereas SCI methods exploit the angular correlations inherent within the scattering process to reconstruct the hidden object. In contrast with WFS approaches, SCI methods do not need long acquisition times or the presence of a guide star2. However, SCI methods are currently limited to imaging sparsely tagged objects in a dark-field scenario, and are strongly impacted by noise from other sources.2 In this work, we establish a technique that allows SCI to image obscured objects in a bright-field scenario.3 Our technique leverages the temporal correlations inherent in the scattering process to distinguish the object signal from the remaining, undesired ‘background’ light contributions. By using a deterministic phase modulator to generate a spatially incoherent light source, the background light contribution is kept constant between different acquisitions and can subsequently be subtracted out. As long as the object moves between acquisitions, the signal from the object can be isolated. The object can be reconstructed from this signal with high fidelity. Using this technique, we experimentally demonstrate successful reconstruction of moving objects hidden behind and between optically translucent materials. Due to the ability to effectively isolate the object signal, our work is not limited to imaging objects in the dark-field case, but also works in bright-field scenarios, with non-emitting objects. This ability opens up many potential applications for imaging in scattering media, such as through turbulent atmosphere or biological tissue, and makes this work relevant to the technical session on ‘Biophotonics in scattering tissue.’ References 1 R. Horstmeyer et al, “Guidestar-assisted wavefront-shaping methods for focusing light into biological tissue,” Nat. Photon. 9, 563-571 (2015). 2O. Katz et al, “Non-invasive single-shot imaging through scattering layers and around corners via speckle correlations,” Nat. Photon. 8, 784-790 (2014). 3M.Cua et al, “Imaging moving targets through scattering media,” O.E. 25(4), 3935-3945 (2017) Please click Additional Files below to see the full abstract