Indraneel Chakraborty

Rolling element bearing design through genetic algorithms

The design of rolling element bearings has been a challenging task in the field of mechanical engineering. While most of the real aspects of the design are never disclosed by bearing manufacturers, the common engineer is left with no other alternative than to refer to standard tables and charts containing the bearing performance characteristics. This paper presents a more viable method to solve this problem using genetic algorithms (GAs). Since the algorithm is basically a guided random search, it weakens the chances of getting trapped in local maxima or minima. The method used has yielded improved performance parameters than those catalogued in standard tables. *Indraneel Chakraborty is currently with Massachusetts Institute of Technology and can be reached at indranil@mit.edu †Vinay Kumar is currently with Mindtree Consulting, India and can be reached at vinayk@mindtree.com

Clock synchronization for wireless networks

Time synchronization is a fundamental service in many wireless applications. While the synchronization problem is well-studied in traditional wired networks, physical constraints of the wireless medium impose a unique set of challenges. We present a novel time synchronization algorithm which is highly energy efficient and failure/recovery-tolerant. Our algorithm allows nodes to synchronize to sources of real time such as GPS when such signals are available, but continues to synchronize nodes to each other, even in the absence of GPS. In addition, the algorithm satisfies a relaxed gradient property, in which the degree of synchronization between nodes varies as a linear function of their distance. Thus, nearby nodes are highly synchronized, which is desirable in many wireless applications.

MAC scheduling policies with reduced power consumption and bounded packet delays for centrally controlled TDD wireless networks

In networks with mobile nodes, power consumption is an important constraint due to the limited battery power available at the mobile nodes. Reduction of power consumption in mobile devices can be achieved by keeping these devices in a low power (standby) mode during periods of inactivity. This may, however, result in increased end-to-end delays leading to violation of the quality of service (QoS) parameters. We propose medium access control (MAC) scheduling policies for centrally controlled TDD wireless systems. The proposed policies reduce the power consumption of mobile devices by putting them into low power mode intelligently, using probabilistic estimates of inactivity based on the previous traffic arrival pattern. The policies ensure that the QoS parameters such as end-to-end packet delays are not violated.

Policies for increasing throughput and decreasing power consumption in Bluetooth MAC

Bluetooth is a fast emerging standard for indoor picocellular wireless networks. Power is at a premium in typical Bluetooth devices like palmtops, PDAs, laptops and mobile phones. The Bluetooth standard defines various modes for reducing power consumption of the devices by reducing their transmission and reception activities. System throughput can be increased by keeping Bluetooth devices in low power mode in case of low data rates at those devices, by avoiding unnecessary polling packets. In this paper, we propose policies for scheduling and switching of power modes of Bluetooth devices for increasing throughput and decreasing power consumption. All the proposed schemes, along with a policy where all the devices are always in active mode and a policy with previous information of packet arrival times, are implemented on a Bluetooth simulator for comparing their performance. Performance of the policies is compared for different traffic models and actual traffic traces. The policies are found to perform well in terms of power savings and throughput enhancement.

Housing Price Booms and Crowding-Out Effects in Bank Lending

Analyzing the period 1988–2006, we document that banks that are active in strong housing markets increase mortgage lending and decrease commercial lending. Firms that borrow from these banks have significantly lower investment. This is especially pronounced for firms that are more capital constrained or borrow from more-constrained banks. Various extensions and robustness analyses are consistent with the interpretation that commercial loans were crowded out by banks responding to profitable opportunities in mortgage lending, rather than with a demand-based interpretation. The results suggest that housing prices appreciations have negative spillovers to the real economy, which were overlooked thus far. Received November 29, 2016; editorial decision January 12, 2018 by Editor David Hirshleifer. Authors have furnished an Internet Appendix, which is available on the Oxford University Press Web Site next to the link to the final published paper online.In the recent recession and current economic recovery, policymakers have supported asset prices in the U.S. treasury and mortgage markets, expecting that improvement in the balance sheet of banks will lead to more commercial lending. In general, we document that increases in housing prices in a bank’s deposit base lead banks to decrease commercial lending. Further, we find that a one-standard deviation increase in housing prices is associated with a 10.3 percentage point decrease in investment of borrowing firms and a 4.2 percentage point decrease in leverage. These results suggest that when asset prices increase in one sector (such as the housing market), banks may respond by reallocating capital away from other sectors (such as commercial lending) towards the supported sectors. JEL Code: G21, G31, G32.

Managing Performance Signals Through Delay: Evidence from Venture Capital

This paper examines whether agency conflicts during venture capital (VC) fundraising impact investment behavior. Using novel investment-level decisions of VCs in the process of raising new funds, we find that venture capitalists take actions hidden from their investors, i.e. limited partners (LPs), that delay revealing negative information about VC fund performance until after a new fund is raised. After fundraising is complete, write-offs double and reinvestments in relatively worse off entrepreneurial firms increase. We find that these observations cannot be explained by strategic bundling of news or effort constraints due to the newly raised fund. Funds with both long and short fundraising track record exhibit this behavior and the delay is costly for fund investors (LPs). This strategic delay shows that fundraising incentives have real impacts on VC fund investment decisions, which are often difficult for LPs to observe.

Monetary Stimulus and Bank Lending

In recent business cycle downturns, monetary policymakers worldwide have sought to stimulate their economies by conducting asset purchases. The U.S. Federal Reserve purchased both agency mortgage-backed securities (MBS) and Treasury (TSY) securities, which are generally thought to be comparable in credit quality and stimulative effects. This paper investigates the effect of such purchases on mortgage lending, commercial lending, and firm investment using micro-level data. We find that MBS and TSY purchases have asymmetric effects. In response to MBS purchases, banks that are active in the MBS market increase their mortgage origination market share, compared to other banks. At the same time, these banks reduce commercial lending. As a result, firms that borrow from these banks decrease investment. The effect of TSY purchases is either positive, as expected, or insignificant in most cases. Our results suggest different effects depending on the type of asset purchased, that MBS purchases cause distortionary effects across banks and firms, and that TSY purchases did not cause a large positive stimulus to the economy through the bank lending channel.

Adaptive routing for ad hoc wireless networks providing QoS guarantees

A cluster-based route discovery and dynamic route management protocol for ad hoc networks with inaccurate information for given QoS (quality of service) requirements has been proposed and compared with existing routing protocols. The proposed scheme is much more scalable, the route discovery is faster (O(logN) against O(N), N being the number of nodes) and it also guarantees QoS - a feature which has not been incorporated in any existing protocol. Also, features such as local dynamic route maintenance, loop avoidance load balancing, delay bounded routing and guaranteed rate routing have been included in the architecture of ACRQ. ACRQ can also work in case of inaccurate information by assigning weights according to the probability of each information being true. This information is then used for routing decisions. Furthermore, ACRQ takes advantage of the MAC characteristics of present wireless technologies such as master-driven communication in Bluetooth. Master-driven systems encourage cluster based routing, which is also helpful for scalability. A distributed algorithm for clustering and election of cluster heads (in ACRQ protocol) with only one round of message exchange has been proposed as well.

Credit Default Swaps and Moral Hazard in Bank Lending

We analyze whether introduction of Credit Default Swaps (CDSs) on borrowers’ debt misaligns incentives between banks and borrowers in the private debt market. In contrast to predictions of an empty creditor problem, after a covenant violation, CDS firms do not become distressed or go bankrupt at a higher rate than firms without CDS. But, consistent with lender moral hazard, CDS firms do not decrease their investment after a covenant violation, even those that are more prone to agency issues. In line with increased bargaining power of lenders, CDS firms pay a significantly higher spread on loans issued after covenant violations compared with non-CDS firms that violate covenants. These results are magnified when lenders have weaker incentives to monitor (higher purchase of credit derivatives, higher amount of securitization and higher noninterest income). Finally, consistent with our evidence of lender moral hazard, we document positive abnormal returns around bank loan announcements only for nonCDS firms, but not for CDS firms. JEL Code: G21, G31, G32.

Income Inequality, Tax Policy, and Economic Growth

We investigate how the reduction of income inequality through tax policy affects economic growth. Taxation at different points of the income distribution has heterogeneous impacts on households’ incentives to work, invest, and consume. Using US state‐level data and micro‐level household tax returns over the last three decades, we find that reducing income inequality between low and median income households improves economic growth. However, reducing income inequality through taxation between median and high‐income households reduces economic growth. These asymmetric economic growth effects are attributable both to supply‐side factors (i.e. changes in small business activity and labour supply) and to consumption demand.