393 research outputs found
Electrodeposition of highly active lithium cobalt oxide thin film anodes in platinum metal group-free photoelectrochemical cells
No full textIn the development of high-performance, commercially-scalable photoelectrochemical cells (PECs) for solar-driven hydrogen production, effective and low-cost anodes must be engineered for long-term operation in alkaline solution. Lithium cobalt oxide (LiCoO2) has been studied as a highly active and stable catalyst for the anodic oxygen evolution reaction (OER) in its delithiated cubic spinel polymorph, LiCo2O4. Drawing inspiration from the dimensionally stabilized anode (DSA) configuration used for continuous electrochemical chlorine generation, a thin film of LixCoO2 has been electrodeposited onto a passivated TiOx/Ti support for functional integration as the dark anode in the PEC device. Kinetic performance as evaluated by cyclic and linear sweep voltammetry resulted in geometric current densities of 10 mA/cm2 (corresponding to 10% photoelectrochemical conversion) achieved at 430 mV overpotential. Long-term stability measurements evaluated at 10 mA/cm2 demonstrate continuous operation for up to 13 days with minimal loss in activity. Characterization via x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy coupled with electron dispersive spectroscopy give insight into the structure-property relationships responsible for the measured high electrochemical performance.M.S.Includes bibliographical referencesby Ajay R. Kash
I-TCP: Indirect TCP for Mobile Hosts
No full textIP-based solutions to accommodate mobile hosts within existing internetworks do not address the distinctive features of wireless mobile computing. IP-based transport protocols thus suffer from poor performance when a mobile host communicates with a host on the fixed network. This is caused by frequent disruptions in network layer connectivity due to — i) mobility and ii) unreliable nature of the wireless link. We describe the design and implementation of I-TCP, which is an indirect transport layer protocol for mobile hosts. I-TCP utilizes the resources of Mobility Support Routers (MSRs) to provide transport layer communication between mobile hosts and hosts on the fixed network. With I-TCP, the problems related to mobility and the unreliability of wireless link are handled entirely within the wireless link; the TCP/IP software on the fixed hosts is not modified. Using I-TCP on our testbed, the throughput between a fixed host and a mobile host improved substantially in comparison to regular TCP.Technical report DCS-TR-31
Selective Silylation of ß-Cyclodextrin
No full textSonication was used to silylate the seven primary alcohols of ß-cyclodextrin. The sonication reaction produced yields comparable to published procedures and reduced the time of silylation by 75% (1).
The reaction of ß-cyclodextrin and tert-Butyldimethylsilyl chloride in dry pyridine resulted in a 71% yield of Heptakis(6-O-tert-Butyldimethylsilyl)- ß-cyclodextrin.¹ H NMR and ¹³C NMR were used to characterize the product
IP multicast extensions for mobile internetworking
No full textThis paper deals with multicasting in an internetwork with mobile hosts, particularly with regard to Mobile-IP and Distance Vector Multicast Routing (DVMRP) protocols. When the source of a multicast datagram is a mobile host (MH), the datagram may not reach all group members to which the datagram is addressed, including other mobile hosts. When the source is a static host and the multicast group includes mobile hosts, a mobile group member may receive datagrams in one cell but not in another. Further, when a MH enters a cell which contains no other member of the same group, the MH will experience a delay before it starts receiving datagrams addressed to that group. Mobility between campuses, which result in a MH acquiring an additional unicast address, also has an effect on multicast routing. We propose enhancements to DVMRP executed at the Mobility Support Routers (MSR) that ensure correct forwarding of multicast datagrams to and from mobile hosts. Our solutions do not require any change at hosts and routers unaware of mobility, i.e. the modifications are limited to MSRs and MHs. We also describe an implementation incorporating a subset of our proposals. Lastly, we show that alternate styles of multicasting or mobile networking, viz. link-state (MOSPF ) and IETF proposal, will face similar problems and our proposed solutions are still valid in their context.Technical report lcsr-tr-24
FUNDAMENTAL TECHNOLOGIES FOR THE OPTO MECHANICAL GYROSCOPE
No full text138 pagesOpto-mechanics is the convergence of optics and mechanics towards the understanding of novel physical phenomenon and the achievement of cutting edge applications. From the effects of radiation pressure on the study of gravitational waves in a LIGO to the study of the quantum mechanical ground state of a simple harmonic oscillator, opto-mechanics spans a very wide range of the physical world. Optical systems with their capability of high sensitivity have been evaluated for applications as sensors like heart rate monitors, gas sensors and LIDARs. There has also been a growing demand for more robust, sensitive, low cost and easy to integrate gyroscopes for applications ranging from defense to autonomous driving. While there are existing technologies for high performance gyroscopes like the ring laser gyroscope and the machined hemispherical resonator gyroscope, these can be large, expensive and unwieldy rendering them unsuitable for a wide variety of applications. MEMS based gyroscopes are low-cost, come in smaller packages and are easy to integrate into systems but they might not have the high performance desired in these new demanding applications. Opto-mechanics has the potential to bridge the gap by combining MEMS and optics to leverage the high sensitivity of optics with the low cost and ease of integration of MEMS devices. The work presented in this thesis showcases some of the fundamental technologies needed for an opto-mechanical gyroscope (OMG). First is the scale hemispherical opto-mechanical resonator that is meant to incorporate the highly desirable mechanical properties of the cm scale hemispherical resonator gyroscope. These silicon dioxide resonators were fabricated in a MEMS centric process flow. The mechanical modes were optically sensed with a tapered optical fiber coupled to a toroidal optical cavity fabricated on the lip of the hemispherical resonator. Next is the development of silicon opto-mechanical wineglass mode resonators with on-chip waveguides. The silicon-on-insulator (SOI) platform employed here allows for better integration of the electro-static actuation and opto-mechanical sensing of the wineglass modes. The two orthogonal n=2 wineglass modes can be used for gyroscopy. Here, I first present the path towards closing the loop on the gyroscope drive wineglass mode. The differential electro-static actuation scheme achieved an 18db relative suppression of the undesired radial mode relative to the wineglass mode. The differential opto-mechanical sensing achieved a 5.4db enhancement of the drive wineglass mode detection and a further 11dB attenuation of radial mode. The suppression of the spurious modes relative to the desired wineglass mode allows a path for closing the oscillator loop on the wineglass mode without the need for additional filters. Next, I present the electro-static actuation of the drive wineglass mode and the opto-mechanical sensing of the orthogonal sense wineglass mode around 22MHz. The resonator was specially designed to achieve a controlled frequency mismatch between these two wineglass modes of only 120KHz and the design allows for tuning this further as needed. Measurements in vacuum showed an optical Q of 61,000 for the optical ring cavity mode and a mechanical Q of 11,500 for the drive wineglass mode and 7,670 for the sense wineglass mode. Last is the work with Lithium Niobate (LN) resonators. LN is of interest for its piezoelectric properties where the large piezoelectric coupling coefficient () allows for efficient electrical actuation of its mechanical modes. There is a potential for leveraging the high efficiency mechanical mode actuation to actuate the drive mode of a gyroscope device. Typically these resonators are actuated with gold but gold has been found to be mechanically lossy. Aluminum was chosen to be the replacement of gold in this work for its lower mechanical losses compared to gold. However, aluminum is very reactive with hydrofluoric acid (HF) which is used as part of the fabrication process of these devices. This necessitated an exploration of passivation methods to protect the aluminum electrodes from HF. Among the various films that I evaluated, a protective film called ProTEK PSB was found to be the most promising in resisting HF while protecting the aluminum electrodes. ProTEK PSB also had a process for its removal after the HF processing. In summary, this work presents some of the fundamental technologies such as a scale high mechanical performance device, a chip scale platform for selective transduction of the wineglass modes and a path towards high efficiency actuation of mechanical modes, all of which could contribute towards building an opto-mechanical gyroscope
Exchange reform, parallel markets, and inflation in Africa : the case of Ghana
No full textThis paper presents a theoretical framework to analyze the issue of exchange rate reform in the presence of parallel markets. In Ghana, which has carried out one of the most thorough structural adjustment programs in Africa, an increasingly high inflation rate has been attributed to major devaluations of the official exchange rate. The authors dispute this conclusion based on careful testing and simulations using a macroeconomic model estimated with Ghanaian data. This model also shows that there is no direct relationship between the official exchange rate and inflation. The results also show that official devaluation had a postive effect on Ghana's budget. Revenue improvements came from three channels: the higher grant aid disbursed at a more depreciated exchange rate, a reduction in the subsidies that had accrued to importers through an overvalued exchange rate, and an increase in export taxes as cocoa farmers increasingly marketed their output through official channels. The official devaluation therefore did not produce higher budget deficits, demand pressure did not spill onto the parallel market, and the exchange premium narrowed considerably. The key to the success of the program was the adequate level of foreign financing, combined with a coherent set of fiscal policies.Access to Markets,Economic Theory&Research,Environmental Economics&Policies,Economic Stabilization,Markets and Market Access
Design and implementation of indirect protocols for mobile wireless
No full textHost mobility within the largely stationary internetwork has been treated thus far as a routing problem, to be solved entirely within the network layer of the ISO/OSI protocol model. However, mobility of host machines from one attachment point to another affects transport and higher layer protocols as well. In addition, the use of wireless links by mobile computers for attachment to the fixed network infrastructure, gives rise to performance problems due to low bandwidth and high error rates that are typical of wireless environments. The existing network protocols do not provide any mechanism to deal with the problems arising out of host mobility and wireless access. Widespread use of mobile and wireless capable computers is also likely to create a demand for new applications that utilize the mobile user's location for accessing information sources. Applications used in mobile wireless environments may also need to adapt to the changes in the characteristics of the wireless medium.
In this dissertation, we consider the problem of supporting distributed applications on mobile wireless computers that need to communicate with peer applications and servers on the wired internetwork. We present the design and implementation of Indirect Protocols, which allow the use of specialized network protocols for the wireless medium and mobile hosts in a way that is backward compatible with the existing protocols used over the wired internetwork. Indirect protocols are based on two key ideas: i) Special treatment of wireless links and mobile computers in an internetwork and ii) Use of mobility support routers (MSRs) as multi-protocol intermediaries. Mobility support routers provide the necessary support to ensure inter-operability with the existing wired network protocols. We show that the use of indirection results in improved performance at the transport layer and provides enhanced functionality at the remote procedure call (RPC) layer.Technical report lcsr-tr-27
Family altruism and incentives
No full textThe author builds on the altruistic model of the family, to explore the strategic interaction between altruistic parents, and selfish children, when children's efforts are endogenous. If there is uncertainty about the amount of income the children will realize, and if parents have imperfect information, the children have an incentive to exert little effort, and to rely on their parent's altruistically motivated transfers. Because of this, parents face a tradeoff between the insurance that bequests implicitly provide their children, and the disincentive to work prompted by their altruism. The author shows that if parents can credibly commit to a pattern of transfers, they will choose not to compensate children in bad outcomes, as much as predicted by the standard (no uncertainty, no asymmetric information) dynastic model of the family. Alternatively, parents may choose to forgo any insurance, and offer a fixed level of bequest, to elicit greater effort from their children. The optimal transfers structure that the author derives, reconciles the predictions of the altruistic family model, with much of the existing evidence on inter-generational transfers, which suggests that parents compensate only partially, or not at all, for earnings differentials among their children. Moreover, the author shows that Ricardian equivalence holds in this setup, except when non-negativity constraints are binding.Economic Theory&Research,Environmental Economics&Policies,Health Economics&Finance,Educational Sciences,Safety Nets and Transfers
Analysis of Public Expenditure on Health Using State Level Data
No full textIncreasingly the governments are facing pressures to increase budgetary allocations to social sectors. Recently there has been suggestion to increase the government budget allocations to health sector and increase it to 3 per cent of GDP. Is this feasible goal and in what time-frame? Health being State subject in India and much depends on the ability of the State governments to allocate higher budgetary support to health sector. This inter alia depends on what are current levels of spending, what target spending as per cent of income the States assume to spend on health and given fundamental relationship between income levels and public expenditures, how fast expenditures can respond to rising income levels. We present analysis of public expenditures on health using state level public health expenditure data to provide preliminary analysis on these issues. The findings suggest that at state level governments have target of allocating only about 0.43 per cent of SGDP to health and medical care. This does not include the allocations received under central sponsored programmes such as family welfare. Given this level of spending at current levels and fiscal position of state governments the goal of spending 2 to 3 per cent of GDP on health looks very ambitious task. The analysis also suggests that elasticity of health expenditure when SGDP changes in only 0.68 which suggest that for every one percent increase in state per capita income the per capita public healthcare expenditure has increased by around 0.68 per cent.
Public finance in adjustment programs
No full textThis paper reviews the experience with public finance issues under adjustment programs. This experience shows that fiscal changes are often triggered by budget and balance of payment crises. As a result, short-term considerations have dominated the policy measures introduced. Traditional stabilization policies usually emphasize measures aimed at reducing aggregate demand. On the fiscal side, this has implied cutbacks in public expenditures. There is, however, growing recognition of the need for more growth oriented adjustment programs, which entail a more comprehensive and durable approach to fiscal reform and therefore require a medium-term perspective. Countries committed to fundamental reform of fiscal and other key policy areas should be able to avail themselves of external financial support that lasts long enough for them to initiate and sustain the change process. They must strike a balance between stabilization and adjustment.Economic Stabilization,Environmental Economics&Policies,Public Sector Economics&Finance,National Governance,Banks&Banking Reform
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