Statistical closed-loop process scheduling

Traditionally, scheduling algorithms have been implemented as open-loop control systems. This allows the operating system to make quick decisions on the order in which tasks should be scheduled without requiring complex calculations. It is very common for a task to be assigned a priority based on its anticipated performance, or based on general process characteristics (i.e., I/O bound versus CPU bound). The problem with this type of scheduling, and this type of control system in general, is that it is rigid and lacks the ability to adjust based on the actual performance of the system and its processes. This work is an examination of a simple closed-loop scheduling algorithm that dynamically adjusts the way tasks are scheduled based on the actual system and process performance. It is believed that by making this change to the scheduling algorithm, several important aspects of system performance will be affected. The system resources can be more efficiently utilized because scheduling parameters are dynamically adjusted to compensate for the current system load. The apparent responsiveness of the system, from the point of view of the applications, will increase because processes will be treated more fairly. Also, the overall system throughput will improve, because the closed-loop control system allows the scheduler to make better decisions on the order in which tasks should be run. The implementation of a closed-loop scheduler will result in an increase in the overhead of the scheduling algorithm; however, it is believed that this increase in overhead will be minimal. Extensive testing of the algorithm using a wide variety of applications will be used to demonstrate that the increase is indeed acceptable, given the other benefits of the algorithm. Due to the fact that the proposed scheduling algorithm is statistical in nature, it does not apply to hard real-time operating systems, but could be used to improve soft real-time operating systems, which have less stringent deadline requirements, and in general purpose time-sharing operating systems. Although this algorithm could have been implemented in any operating system, Linux was chosen as the base platform for this work due to its open source nature. Linux has the additional benefit of providing a well-known environment, and utilities that facilitate the measurements necessary to evaluate the performance of the algorithm. This work demonstrates that increased overhead required for a closed-loop system is reasonable, and that closed-loop scheduling can provide certain benefits over traditional open-loop schedulers. When compared to the original Linux kernel, the throughput performance degraded typically between 1.5% and 2% depending on the process mix; however, some of the changes to the base kernel can be used to explain this performance degradation. The system clock rate was increased from 100 Hz to 1000 Hz to obtain the timer granularity necessary for the closed-loop control system. Previous work measured a 3.1% increase in overhead when using a 1000 Hz system clock. Measurements were taken on a custom version of the original kernel that was built with a 1000 Hz system clock, which support that claim. When compared to the base kernel with a 1000 Hz system clock, the closed-loop scheduler produces better performance. This work also demonstrates the disadvantage of an open-loop scheduler. An application was developed with fixed length CPU bursts and periodic I/O requests to show that blindly giving the CPU to I/O bound processes and using epochs to age processes results in a significant number of unnecessary process switches that inevitably degrades the performance of the machine. The closed-loop scheduling algorithm balances the load across the processes more evenly, resulting in better performance under a high system load

Shareholders, Creditors, and Directors’ Fiduciary Duties: A Law and Finance Approach

The debate surrounding fiduciary duties owed to creditors by directors, especially in the vicinity of insolvency, has resurfaced in light of two court decisions in Canada and the United States. In this paper, we contribute to the discussion by looking at the issue from a corporate finance perspective, where we utilize well-established theorems and results. We show that creditors are able to protect themselves by the use of covenants. While this idea has been reported extensively in previous discussions about fiduciary duties, we focus on studies that show the extent to which creditors use covenants to protect themselves against opportunistic behavior by managers and shareholders. Additionally, we show that debt can actually increase the value of the firm and the shares, and therefore, the idea that shareholders use debt for opportunistic behavior is misplaced. If anything, debt is used to align managerial incentives to maximize the value of the firm. The Fisher Separation theorem is also introduced and used to show that all stakeholders in a firm will want the firm to pursue projects with the maximum net present value. Hence, we propose that fiduciary duties should always be owed to the corporation as a whole, where the main focus of the managers is investing in those projects that have the highest expected net present value

Systematic variation of central mass density slope in early-type galaxies

We study the total density distribution in the central regions ($<\, 1$ effective radius, $R_{\rm e}$) of early-type galaxies (ETGs), using data from the SPIDER survey. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter (DM) halo profile, and leaving stellar mass-to-light ($M_{\rm \star}/L$) ratios as free fitting parameters to the data. For a Navarro et al. (1996) profile, the slope of the total mass profile is non-universal. For the most massive and largest ETGs, the profile is isothermal in the central regions ($\sim R_{\rm e}/2$), while for the low-mass and smallest systems, the profile is steeper than isothermal, with slopes similar to those for a constant-M/L profile. For a concentration-mass relation steeper than that expected from simulations, the correlation of density slope with mass tends to flatten. Our results clearly point to a "non-homology" in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on 25th-28th november 2014, to be published on Astrophysics and Space Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic

Damping and decoherence of a nanomechanical resonator due to a few two level systems

We consider a quantum model of a nanomechanical flexing beam resonator interacting with a bath comprising a few damped tunneling two level systems (TLS's). In contrast with a resonator interacting bilinearly with an ohmic free oscillator bath (modeling clamping loss, for example), the mechanical resonator damping is amplitude dependent, while the decoherence of quantum superpositions of mechanical position states depends only weakly on their spatial separation

DNA replication: archaeal oriGINS

GINS is an essential eukaryotic DNA replication factor that is found in a simplified form in Archaea. A new study in this issue of BMC Biology reveals the first structure of the archaeal GINS complex. The structure reveals the anticipated similarity to the previously determined eukaryotic complex but also has some intriguing differences in the relative disposition of subunit domains

Composição isotópica de Sr, C e O e geoquímica de ETR das rochas carbonáticas do Bloco São Gabriel, Rio Grande do Sul

The São Gabriel Block, located in the central zone of the crystalline basement in the state of Rio Grande do Sul has extensive Neoproterozoic records of the Brasiliano Cycle, recorded in igneous and metamorphic complexes. These complexes also keep sedimentary records of metamorphosed carbonate successions whose tectonic evolution is poorly understood. Therefore, this study aimed to investigate the origin and evolution of carbonate rocks that occur in São Gabriel Block by geochemical characterization of major, trace, REE and Sr, C and O isotopes. Hence, Passo Feio Formation, Cambaí Complex and Coxilha do Batovi Complex were chosen as research areas. The Passo Feio Formation carbonate rocks consist of impure dolomite marbles. The Cambaí Complex samples are classified as impure calcite marbles. Coxilha do Batovi Complex samples include calcite and calc-silicate marbles, some of them with graphite, with quartz rates up to 10% showing the siliciclastic contribution to the protolith. Ages from detrital zircon of chlorite schists rocks from previous works indicate an interval between 770-700 Ma for carbonate deposition in São Gabriel Block. The carbonates from Passo Feio Formation were affected by dolomitization process during or early after its deposition, while the carbonates from Cambaí Complex were not affected by dolomitization. Trace elements and REE geochemistry of marbles indicate preservation of original composition of carbonate protoliths along different 76 metamorphic grades; Coxilha do Batovi Complex (low grade), Passo Feio Formation and Cambaí Complex (medium grade). The integrated analysis of Sr, C and O isotopes from Passo Feio Formation and Cambaí Complex revealed the preservation of primary isotopic values or very close to the original isotopic composition. For the Passo Feio Formation the values are: 0,7074 (Sr87/Sr86), -0,26‰ and 2,44‰ (δ13CPDB) and -5,68 (δ18OPDB). For the Cambaí Complex, these values are: 0,7069 (Sr87/Sr86), 5,75 (δ13CPDB) and -11,64 (δ18OPDB). When compared with seawater Sr, C and O isotopes variations along the Neoproterozoic it appears that Passo Feio Formation and Cambaí Complex are situated in the range between 770 and 730 Ma. Based on these data it is suggested that the São Gabriel Block depositional event occurred between 770-700 Ma. The contextualization of isotopic data in the chronology of the tectonic events recognized in São Gabriel Block allowed estimation of periods of deposition of carbonate rocks of Passo Feio Formation between 770 and 730 Ma, and between 740 and 730 Ma for Cambaí Complex.O Bloco São Gabriel, localizado na zona central do embasamento cristalino do Rio Grande Sul, apresenta extensos registros do Neoproterozóico do Ciclo Brasiliano, contidos em complexos ígneos e metamórficos. Esses complexos também guardam registros sedimentares, com sequências carbonáticas metamorfisadas, cuja evolução tectônica é pouco conhecida. Por essa razão, buscou-se nesse trabalho investigar a origem e a evolução das rochas carbonáticas ocorrentes no Bloco São Gabriel por meio da caracterização geoquímica de elementos maiores, traço, ETR e isótopos de Sr, C e O. Para tanto, foram escolhidas como áreas de pesquisa no Bloco São Gabriel a Formação Passo Feio, o Complexo Cambaí e o Complexo Coxilha do Batovi. As rochas carbonáticas da Formação Passo Feio compreendem dolomita mármores impuros, as amostras do Complexo Cambaí, calcita mármores impuros e os litotipos do Complexo Coxilha do Batovi, mármores calcíticos e calcissilicáticos, alguns ricos em grafita e com percentuais de até 10% de quartzo demonstrando contribuição siliciclástica no protólito. Idades de zircões detríticos de clorita xistos associados com os mármores, obtidos em trabalhos anteriores, indicam um intervalo entre 770 – 700 Ma para a deposição dos carbonatos do Bloco São Gabriel. Os carbonatos da Formação Passo Feio sofreram dolomitização durante ou logo após a deposição, enquanto os carbonatos do Complexo Cambaí não foram afetados pela dolomitização. A geoquímica dos elementos traço e terras raras indica que os mármores analisados preservaram as composições isotópicas originais do protólito nos diferentes graus metamórficos: Complexo Coxilha do Batovi (grau baixo), Formação Passo Feio e Complexo Cambaí (grau médio). A análise integrada dos isótopos de Sr, C e O da Formação Passo Feio e do Complexo Cambaí revelou a preservação de valores isotópicos primários ou muito próximos da composição isotópica original. Na Formação Passo Feio os valores obtidos são: 0,7074 (87Sr/86Sr), -0,26‰ e 2,44‰ (δ13CPDB) e -5,68‰ (δ18OPDB). No Complexo Cambaí, estes valores são: 0,7069 (87Sr/86Sr), 5,75‰ (δ13CPDB) e -11,64‰ (δ18OPDB). Quando comparadas com a curva de variação da razão 87Sr/86Sr e dos valores de δ13C e δ18O da água do mar ao longo do Neoproterozóico, verifica-se que os mármores da Formação Passo Feio e do Complexo Cambaí estão situados no intervalo entre 770 e 730 Ma. A contextualização dos dados isotópicos na cronologia dos eventos tectônicos reconhecidos no Bloco São Gabriel permitiu a estimativa de períodos de deposição das rochas carbonáticas da Formação Passo Feio entre 770 e 730 Ma, e entre 740 e 730 Ma para o Complexo Cambaí