Cost Of Conversions Research Articles

Bandwidth Cost of Code Conversions in Distributed Storage: Fundamental Limits and Optimal Constructions

Erasure codes have become an integral part of distributed storage systems as a tool for providing data reliability and durability under the constant threat of device failures. In such systems, an [ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n, k</i> ] code over a finite field F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>q</i></sub> encodes <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> message symbols from F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>q</i></sub> into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> codeword symbols from F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>q</i></sub> which are then stored on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> different nodes in the system. Recent work has shown that significant savings in storage space can be obtained by tuning <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> to variations in device failure rates. Such a tuning necessitates <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">code conversion</i> : the process of converting already encoded data under an initial [ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n^I, k^I</i> ] code to its equivalent under a final [ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n^F, k^F</i> ] code. The default approach to conversion is to re-encode the data under the new code, which places significant burden on system resources. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Convertible codes</i> are a recently proposed class of codes for enabling resource-efficient conversions. Existing work on convertible codes has focused on minimizing the access cost, i.e., the number of code symbols accessed during conversion. Bandwidth, which corresponds to the amount of data read and transferred, is another important resource to optimize during conversions. In this paper, we study the fundamental limits on bandwidth used during code conversion and present constructions for bandwidth-optimal convertible codes. First, we model the code conversion problem using network information flow graphs with variable capacity edges. Second, focusing on MDS codes and an important parameter regime called the merge regime, we derive tight lower bounds on conversion bandwidth. The derived bounds show that conversion bandwidth can be significantly reduced as compared to the default approach even in regions where it has been shown that access cost cannot be reduced. Third, we present a new construction for MDS convertible codes which matches the proposed lower bound and is thus bandwidth-optimal during conversion.

Distributed Generation and Megacities: Are Renewables the Answer?

Distributed electricity generation is opposite of centralized electricity production, mode that has dominated modern commercial electrical supplies for more than a century. Rather than relying on large central stations (fossil fueled, nuclear, or hydro) and high-voltage transmission lines, distributed electricity generation depends on small-scale, decentralized, local, on-site generation, preferably by tapping renewable energy sources. This arrangement avoids long-distance transmission losses, and, once organized in a web of smart microgrids, its design improves supply stability and reliability and gives users more control. As cost of new renewable energy conversions continues to decline, this form of electricity supply is expected to claim a rising share of overall generation. Indeed, according to Rodan Energy, distributed generation is not just future of electricity, but also the future of energy.

The cost of conversion in robotic and laparoscopic colorectal surgery.

Conversion from minimally invasive to open colorectal surgery remains common and costly. Robotic colorectal surgery is associated with lower rates of conversion than laparoscopy, but institutions and payers remain concerned about equipment and implementation costs. Recognizing that reimbursement reform and bundled payments expand perspectives on cost to include the entire surgical episode, we evaluated the role of minimally invasive conversion in total payments. This is an observational study from a linked data registry including clinical data from the Michigan Surgical Quality Collaborative and payment data from the Michigan Value Collaborative between July 2012 and April 2015. We evaluated colorectal resections initiated with open and minimally invasive approaches, and compared reported risk-adjusted and price-standardized 30-day episode payments and their components. We identified 1061 open, 1604 laparoscopic, and 275 robotic colorectal resections. Adjusted episode payments were significantly higher for open operations than for minimally invasive procedures completed without conversion ($19,489 vs. $15,518, p<0.001). The conversion rate was significantly higher with laparoscopic than robotic operations (15.1 vs. 7.6%, p<0.001). Adjusted episode payments for minimally invasive operations converted to open were significantly higher than for those completed by minimally invasive approaches ($18,098 vs. $15,518, p<0.001). Payments for operations completed robotically were greater than those completed laparoscopically ($16,949 vs. $15,250, p<0.001), but the difference was substantially decreased when conversion to open cases was included ($16,939 vs. $15,699, p=0.041). Episode payments for open colorectal surgery exceed both laparoscopic and robotic minimally invasive options. Conversion to open surgery significantly increases the payments associated with minimally invasive colorectal surgery. Because conversion rates in robotic colorectal operations are half of those in laparoscopy, the excess expenditures attributable to robotics are attenuated by consideration of the cost of conversions.

Multistep Oxidase–Lyase Reactions: Synthesis of Optically Active 2‐Hydroxyketones by Using Biobased Aliphatic Alcohols

AbstractEnzymatic multistep reactions are presently an important research field, from which integrated and efficient synthetic protocols can be created, accompanied by a diminished waste formation (avoiding downstream units operations). This article explores the benzaldehyde lyase (BAL) catalyzed crossed carboligation of benzaldehyde with different aliphatic aldehydes to afford optically active α‐hydroxyketones. To this end, different biobased aliphatic alcohols were in situ oxidized to aldehydes by oxidase from Hansenula sp. and subsequently carboligated with benzaldehyde by BAL in the same reactor system. For short nonbranched aliphatic alcohols, moderate to high conversions in carboligations (15–99 %) with excellent enantioselectivities (98–99 %, R), were achieved. Both enzymes also exhibited activities at high concentrations of benzaldehyde (up to 200 mM) and with butanol as cosolvent, albeit at the cost of lower conversions, presumably owing to kinetic reasons. After needed optimization of the biocatalyst (e.g., through genetic evolution, whole‐cell setup) and the process setup (e.g., stepwise addition of substrates, reaction time), the herein reported concept might provide promising entries in the field of asymmetric synthesis, delivering useful building blocks starting from biobased materials, and in an integrative manner.

A Parallel Processing Uninterruptible Power Supply for Sudden Voltage Fluctuation for Power Management

This paper deals with a parallel processing uninterruptible power supply (UPS) for sudden voltage fluctuation in power management to integrate power quality improvement, load voltage stabilization and UPS. To reduce the complexity, cost and number of power conversions, which results in higher efficiency, only one voltage-controlled voltage source inverter (VCVSI) is used. The VCVSI is connected in series on the DC battery side and in parallel on the AC grid side with a decoupling inductor. The system provides sinusoidal voltage at the fundamental value of 220V/60Hz for the load during abnormal utility power conditions or grid failure. Also, the system can be operated to mitigate the harmonic current and voltage demand from nonlinear loads and provide voltage stabilization for loads when sudden voltage fluctuation occur, such as sag and swell. The experimental results confirm the system protects against outages caused by abnormal utility power conditions and sudden voltage fluctuations and change.

Unified support for integrated all-optical multicast and burst amplification in transparent optical network

To better support transparent optical network, we present a novel scalable structure design based on multi-wavelength conversion (MWC) for integrated optical multicast and burst amplification in this paper. We also propose a corresponding wavelength assignment algorithm to minimize the cost of wavelength conversions in the multicast tree. MWC-based multicast strategy makes it possible to generate data copies through less processes and simplifies the wavelength assignment problem. Meanwhile, the generated data copies are used as complementary signals to compensate the power variations of original signal for Erbium-doped fiber amplifiers transient suppression. Experiments are conducted to demonstrate the performance of both burst amplification and multicast data generation in one MWC process. Simulation results are given for our new wavelength assignment algorithm, and advantages are shown over greedy algorithms.

The abstract vector processor

The abstract vector processing unit (VPU) is a virtual VPU that represents a set of real VPUs. It has an idealised instruction set and constraints common to the VPUs that it represents. Together, the idealised instruction set and common constraints allow programs to be portable and to perform efficiently on the real VPUs being represented. The abstract VPU is suitable for programmers who want the performance advantages of using the VPU directly, without being restricted to a particular VPU. An abstract VPU implementation, Vector Virtual Machine (VVM), is presented in this paper. VVM is designed to represent desktop VPUs, such as AltiVec, and to support the creation of a generic, vectorised, machine-vision library. Constraints common to desktop VPUs that VVM are short vectors, fixed vector sizes, and fast access to aligned memory addresses only. To support the creation of a generic, vectorised, machine-vision library, VVM has traits, templated vectors, constant scalar count vectors, and uses consistent functions for scalars and vectors where possible. Because VVM has constant scalar count, each VVM vector can consist of more than one scalar or VPU vector. Since the cost of type conversions is large for VPU programs, VVM only supports explicit type conversions. Ideally, an abstract VPU should have no overheads; that is be zero-cost. Function overloading and expression templates were tested to investigate the possibility of creating a zero-cost implementation of VVM using only Standard C++ and Apple's GCC 3.1 20021003 compiler. Results show that in this environment, zero-cost can be achieved only when processing VVM vectors that contain a single scalar or VPU vector. For expressions involving one to five additions, function overloading was at worst 3.6% slower than hand-coded programs when processing VVM vectors with one scalar or VPU vector. Unfortunately, for VVM vectors with four VPU vectors, function overloading was at worst 23.0% slower. For the same kind of expressions, the expression templates implementation was up to 888.3% slower. It was comparable to hand-coded programs only for expressions involving only one addition between VVM vectors that contain four VPU vectors. When a VPU is available, only char VVM vectors will consist of one VPU vector. In scalar mode, all VVM vectors will consist of one scalar. Thus, with Apple GCC 3.1 20031003, a VVM implementation based on function overloading has minimal overheads only for applications where most operations involve char types. This implementation's performance is adequate for creating a generic, vectorised, machine-vision library because most image processing operations operate on char types.

ILP-based cost-optimal DSP synthesis with module selection and data format conversion

In high-level synthesis, a data flow graph (DFG) description of an algorithm is mapped onto a register transfer level description of an architecture. Each node of the DFG is scheduled to a specific time and allocated to a processor. In this paper, we present new integer linear programming (ILP) models which generate a blocked schedule for a DFG with automatic retiming, pipelining, and unfolding while performing module selection and dataformat conversion. A blocked schedule is a schedule which overlaps multiple iterations of the DFG to guarantee a processor optimal schedule. During module selection an appropriate processor is chosen from a library of processors to construct a cost optimal architecture. Furthermore, we also include the cost and latency of data format conversions between processors of different implementation styles. We also present a new formulation for minimizing the unfolding factor of the blocked schedule. The approach presented in this paper is the only systematic approach proposed so far to include implicit unfolding and to perform synthesis using nonuniform processor styles and data format converters.

Phaseout Of CFCs Leads To Unexpected Problems

When the use of the chlorofluorocarbon CFC-12 (CCl 2 F 2 ) as the coolant in new auto air conditioners was totally phased out in 1995, it was envisioned that the transition to the use of ozone-friendly hydrofluorocarbon HFC-134a (CH 2 FCF 3 ) would be fairly smooth. All new car air conditioners would be cooled with HFC-134a, and older equipment would be recharged with recycled CFC-12 or converted to the use of HFC-134a. Virtually all the used CFC-12 would be recycled. Instead, the transition has run into unexpected difficulties, in part because of the entrepreneurial nature of U.S. society and the high cost of recycled CFC-12 and air-conditioner conversions, which now average $350 to $800 per car. These costs and consumer confusion as to just what is acceptable in their cars have created a market for some less than perfect products. Some companies have advertised and sold HFG 134a as a dropin replacement for CFG12 for the do-it-yourselfer. Some companies have advertised ...

The Transactions Demand for Cash: A Note on the Baumol-Tobin Theory

expenditure. In Baumol's formulation, cash is obtained by borrowing-although all of the cash does not have to be borrowed at once; it may be borrowed intermittently over time. The advantage is the smaller interest cost; the disadvantage is the cost of the additional conversions to cash. In Tobin's formulation, all the cash is available at once although part of it may be converted into an earning asset such as saving deposits, and converted back into cash intermittently over time. The advantage is the interest earned on the deposits; the disadvantage is the cost of the conversions. There is a constant rate of expenditure throughout a given period in the Baumol-Tobin model, and the cost of a conversion is linear in the amount of the conversion.1 The interest rate for the period is constant, and the interest and the conversion costs occur at the end of the period without affecting the volume of transactions within the period. To follow Tobin's formulation, the number of conversions, their timing and their sizes are determined to maximize the net revenue from the transactions balance. The main conclusions are that the average cash balance varies inversely with the interest rate, and less than proportionally with the volume of transactions. Further, the conversions are spaced at intervals of equal length, except that the first interval is extended in the presence of variable conversion costs.