scholarly journals Effectiveness of Rack-Level Fans—Part I: Energy Savings Through Consolidation

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Richard Eiland ◽  
John Edward Fernandes ◽  
Bharath Nagendran ◽  
Veerendra Mulay ◽  
Dereje Agonafer
Keyword(s):  
Energy Savings ◽  
Total Efficiency ◽  
Single Server ◽  
Case Scenario ◽  
Double Peak ◽  
Similar Reduction ◽  
Worst Case ◽  
Linear Dimensions ◽  
Initial Characterization

In general, smaller fans operate at lower efficiencies than larger fans of proportional linear dimensions. In this work, the applicability of replacing smaller, 60 mm baseline fans from within the chassis of web servers with an array of larger, geometrically proportional 80 mm and 120 mm fans consolidated to the back of a rack is experimentally tested. Initial characterization of the selected fans showed that the larger fans operate at double peak total efficiency of the smaller fans. A stack of four servers were used in a laboratory setting to represent a rack of servers. When all four servers were stressed at uniform computational loadings, the 80 mm fans resulted in 50.1–52.6% reduction in total rack fan power compared to the baseline fans. The 120 mm fans showed similar reduction in rack fan power of 47.6–54.0% over the baseline. Since actual data centers rarely operate at uniform computational loading across servers in a rack, a worst case scenario test was conceived in which the array of larger fans were controlled by a single server operating at peak computational workload while the other three in the rack remained idle. Despite significant overcooling in the three idle servers, the 80 mm and 120 mm fan configurations still showed 35% and 34% reduction in total rack fan power compared to the baseline fans. The findings strongly suggest that a rack-level fan scheme in which servers share airflow from an array of consolidated larger fans is superior to traditional chassis fans.

scholarly journals Multiserver queueing networks and the tandem queue model

1998 ◽  
Vol 11 (3) ◽  
pp. 377-390
Author(s):  
Pierre Le Gall
Keyword(s):  
Queueing Networks ◽  
The Other ◽  
Single Server ◽  
Tandem Queue ◽  
Case Scenario ◽  
Worst Case ◽  
Worst Case Scenario ◽  
Other Hand ◽  
Queueing Delay ◽  
Queue Model

Using a tandem queue model we evaluate the local “endogenous” (= internal) queueing delay in single server and multiserver queueing networks. The new concept of the apparent overall upstream queueing delay(as perceived by the downstream network) allows us to analyze the distribution of this local queue by interpolating between the distributions of the tandem queue (generated by a concentration tree) and the isolated G/G/squeue. The interpolation coefficients depend on the proportion of “premature departures”, typically interfering in the upstream stage and leaving the considered path without being offered to the considered local queue. On the other hand, local “exogenous” arrivals (from outside the network) require the introduction of the “interference delay” concept. Finally, in the case of single server queueing networks, we stress the need to extend the capacities of the buffers, by considering the “worst case” scenario and by using an “equivalent tandem queue” model.

scholarly journals Towards Enhanced System Efficiency while Mitigating Row Hammer

2021 ◽  
Vol 18 (4) ◽  
pp. 1-26
Author(s):  
Kaustav Goswami ◽  
Dip Sankar Banerjee ◽  
Shirshendu Das
Keyword(s):  
Energy Savings ◽  
Random Access ◽  
Spin Transfer Torque ◽  
Lookup Table ◽  
Case Scenario ◽  
Detection Mechanism ◽  
Worst Case ◽  
Extensive Evaluation ◽  
Proposed Model ◽  
Handling Technique

In recent years, DRAM-based main memories have become susceptible to the Row Hammer (RH) problem, which causes bits to flip in a row without accessing them directly. Frequent activation of a row, called an aggressor row , causes its adjacent rows’ ( victim ) bits to flip. The state-of-the-art solution is to refresh the victim rows explicitly to prevent bit flipping. There have been several proposals made to detect RH attacks. These include both probabilistic as well as deterministic counter-based methods. The technique of handling RH attacks, however, remains the same. In this work, we propose an efficient technique for handling the RH problem. We show that the mechanism is agnostic of the detection mechanism. Our RH handling technique omits the necessity of refreshing the victim rows. Instead, we use a small non-volatile Spin-Transfer Torque Magnetic Random Access Memory (STTRAM) that ensures no unnecessary refreshes of the victim rows on the DRAM device and thus allowing more time for normal applications in the same DRAM device. Our model relies on the migration of the aggressor rows. This accounts for removing blocking of the DRAM operations due to the refreshing of victim rows incurred in the previous solution. After extensive evaluation, we found that, compared to the conventional RH mitigation techniques, our model minimizes the blocking time of the memory that is imposed due to explicit refreshing by an average of 80.72% in the worst-case scenario and provides energy savings of about 15.82% on average, across different types of RH-based workloads. A lookup table is necessary to pinpoint the location of a particular row, which, when combined with the STTMRAM, limits the storage overhead to 0.39% of a 2 GB DRAM. Our proposed model prevents repeated refreshing of the same victim rows in different refreshing windows on the DRAM device and leads to an efficient RH handling technique.

Reducing Probabilistic Weather Forecasts to the Worst Case Scenario: Anchoring Effects

2008 ◽  
Author(s):  
Sonia Savelli ◽  
Susan Joslyn ◽  
Limor Nadav-Greenberg ◽  
Queena Chen
Keyword(s):  
Case Scenario ◽  
Worst Case ◽  
Weather Forecasts ◽  
Worst Case Scenario ◽  
Anchoring Effects

EXPEDITION TO MALI, 2020

2020 ◽  
pp. 12-28
Author(s):  
D. V. Vaniukova ◽  
◽  
P. A. Kutsenkov ◽  
Keyword(s):  
Mass Murder ◽  
The State ◽  
Case Scenario ◽  
Worst Case ◽  
Traditional Art ◽  
Peter The Great ◽  
State Museum ◽  
Bobo Dioulasso ◽  
Oriental Studies ◽  
The Village

The research expedition of the Institute of Oriental studies of the Russian Academy of Sciences has been working in Mali since 2015. Since 2017, it has been attended by employees of the State Museum of the East. The task of the expedition is to study the transformation of traditional Dogon culture in the context of globalization, as well as to collect ethnographic information (life, customs, features of the traditional social and political structure); to collect oral historical legends; to study the history, existence, and transformation of artistic tradition in the villages of the Dogon Country in modern conditions; collecting items of Ethnography and art to add to the collection of the African collection of the. Peter the Great Museum (Kunstkamera, Saint Petersburg) and the State Museum of Oriental Arts (Moscow). The plan of the expedition in January 2020 included additional items, namely, the study of the functioning of the antique market in Mali (the “path” of things from villages to cities, which is important for attributing works of traditional art). The geography of our research was significantly expanded to the regions of Sikasso and Koulikoro in Mali, as well as to the city of Bobo-Dioulasso and its surroundings in Burkina Faso, which is related to the study of migrations to the Bandiagara Highlands. In addition, the plan of the expedition included organization of a photo exhibition in the Museum of the village of Endé and some educational projects. Unfortunately, after the mass murder in March 2019 in the village of Ogossogou-Pel, where more than one hundred and seventy people were killed, events in the Dogon Country began to develop in the worst-case scenario: The incessant provocations after that revived the old feud between the Pel (Fulbe) pastoralists and the Dogon farmers. So far, this hostility and mutual distrust has not yet developed into a full-scale ethnic conflict, but, unfortunately, such a development now seems quite likely.

Risk-Based Robust Bidding Strategies for EVs’ Aggregators in Day-ahead Markets with Uncertainty

2020 ◽  
Author(s):  
Ahmed Abdelmoaty ◽  
Wessam Mesbah ◽  
Mohammad A. M. Abdel-Aal ◽  
Ali T. Alawami
Keyword(s):  
Robust Optimization ◽  
Electricity Market ◽  
Real Life ◽  
Optimization Approach ◽  
Case Scenario ◽  
Worst Case ◽  
Bidding Strategies ◽  
Wind Generators ◽  
Proposed Model ◽  
Optimal Bidding

In the recent electricity market framework, the profit of the generation companies depends on the decision of the operator on the schedule of its units, the energy price, and the optimal bidding strategies. Due to the expanded integration of uncertain renewable generators which is highly intermittent such as wind plants, the coordination with other facilities to mitigate the risks of imbalances is mandatory. Accordingly, coordination of wind generators with the evolutionary Electric Vehicles (EVs) is expected to boost the performance of the grid. In this paper, we propose a robust optimization approach for the coordination between the wind-thermal generators and the EVs in a virtual<br>power plant (VPP) environment. The objective of maximizing the profit of the VPP Operator (VPPO) is studied. The optimal bidding strategy of the VPPO in the day-ahead market under uncertainties of wind power, energy<br>prices, imbalance prices, and demand is obtained for the worst case scenario. A case study is conducted to assess the e?effectiveness of the proposed model in terms of the VPPO's profit. A comparison between the proposed model and the scenario-based optimization was introduced. Our results confirmed that, although the conservative behavior of the worst-case robust optimization model, it helps the decision maker from the fluctuations of the uncertain parameters involved in the production and bidding processes. In addition, robust optimization is a more tractable problem and does not suffer from<br>the high computation burden associated with scenario-based stochastic programming. This makes it more practical for real-life scenarios.<br>

scholarly journals Identification and initial characterization of POLIII-driven transcripts by msRNA-sequencing.

RNA Biology ◽  
2021 ◽  
Author(s):  
Peter Zorn ◽  
Danny Misiak ◽  
Michael Gekle ◽  
Marcel Köhn
Keyword(s):  
Initial Characterization

scholarly journals A Thermally Conductive Pt/AAO Catalyst for Hydrogen Passive Autocatalytic Recombination

Catalysts ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 491
Author(s):  
Alina E. Kozhukhova ◽  
Stephanus P. du Preez ◽  
Aleksander A. Malakhov ◽  
Dmitri G. Bessarabov
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Combustion Temperature ◽  
Volume Fraction ◽  
Morphological Characteristics ◽  
Al Alloy ◽  
Impregnation Method ◽  
Case Scenario ◽  
Worst Case ◽  
Thermal Distribution

In this study, a Pt/anodized aluminum oxide (AAO) catalyst was prepared by the anodization of an Al alloy (Al6082, 97.5% Al), followed by the incorporation of Pt via an incipient wet impregnation method. Then, the Pt/AAO catalyst was evaluated for autocatalytic hydrogen recombination. The Pt/AAO catalyst’s morphological characteristics were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average Pt particle size was determined to be 3.0 ± 0.6 nm. This Pt/AAO catalyst was tested for the combustion of lean hydrogen (0.5–4 vol% H2 in the air) in a recombiner section testing station. The thermal distribution throughout the catalytic surface was investigated at 3 vol% hydrogen (H2) using an infrared camera. The Al/AAO system had a high thermal conductivity, which prevents the formation of hotspots (areas where localized surface temperature is higher than an average temperature across the entire catalyst surface). In turn, the Pt stability was enhanced during catalytic hydrogen combustion (CHC). A temperature gradient over 70 mm of the Pt/AAO catalyst was 23 °C and 42 °C for catalysts with uniform and nonuniform (worst-case scenario) Pt distributions. The commercial computational fluid dynamics (CFD) code STAR-CCM+ was used to compare the experimentally observed and numerically simulated thermal distribution of the Pt/AAO catalyst. The effect of the initial H2 volume fraction on the combustion temperature and conversion of H2 was investigated. The activation energy for CHC on the Pt/AAO catalyst was 19.2 kJ/mol. Prolonged CHC was performed to assess the durability (reactive metal stability and catalytic activity) of the Pt/AAO catalyst. A stable combustion temperature of 162.8 ± 8.0 °C was maintained over 530 h of CHC. To confirm that Pt aggregation was avoided, the Pt particle size and distribution were determined by TEM before and after prolonged CHC.

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