scholarly journals Frequency estimation under local differential privacy

2021 ◽  
Vol 14 (11) ◽  
pp. 2046-2058
Author(s):  
Graham Cormode ◽  
Samuel Maddock ◽  
Carsten Maple
Keyword(s):  
Large Scale ◽  
Differential Privacy ◽  
Frequency Estimation ◽  
Careful Choice ◽  
The Core ◽  
Private Collection ◽  
Privacy Model ◽  
Common Framework ◽  
Heavy Hitter ◽  
Series Of Experiments

Private collection of statistics from a large distributed population is an important problem, and has led to large scale deployments from several leading technology companies. The dominant approach requires each user to randomly perturb their input, leading to guarantees in the local differential privacy model. In this paper, we place the various approaches that have been suggested into a common framework, and perform an extensive series of experiments to understand the tradeoffs between different implementation choices. Our conclusion is that for the core problems of frequency estimation and heavy hitter identification, careful choice of algorithms can lead to very effective solutions that scale to millions of users.

scholarly journals Local Differential Privacy for Evolving Data

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Matthew Joseph ◽  
Aaron Roth ◽  
Jonathan Ullman ◽  
Bo Waggoner
Keyword(s):  
Large Scale ◽  
Differential Privacy ◽  
Statistical Information ◽  
Underlying Distribution ◽  
Specific Distribution ◽  
Time Period ◽  
Long Time ◽  
Heavy Hitter ◽  
Single Use ◽  
A New Technique

There are now several large scale deployments of differential privacy used to collect statistical information about users. However, these deployments periodically recollect the data and recompute the statistics using algorithms designed for a single use. As a result, these systems do not provide meaningful privacy guarantees over long time scales. Moreover, existing techniques to mitigate this effect do not apply in the “local model” of differential privacy that these systems use. In this paper, we introduce a new technique for local differential privacy that makes it possible to maintain up-to-date statistics over time, with privacy guarantees that degrade only in the number of changes in the underlying distribution rather than the number of collection periods. We use our technique for tracking a changing statistic in the setting where users are partitioned into an unknown collection of groups, and at every time period each user draws a single bit from a common (but changing) group-specific distribution. We also provide an application to frequency and heavy-hitter estimation.

Creating a local food procurement community of practice: The Alberta Flavour Learning Lab

2019 ◽  
Vol 6 (1) ◽  
pp. 155-169 ◽  
Author(s):  
Mary Anne Beckie ◽  
Leanne Hedberg ◽  
Jessie Radies
Keyword(s):  
Community Of Practice ◽  
Large Scale ◽  
Food System ◽  
Local Food ◽  
Provincial Government ◽  
Local Foods ◽  
Social Infrastructure ◽  
City Region ◽  
Physical Scale ◽  
Common Framework

In order for local food initiatives (LFIs) to have a transformative effect on the larger food system, greater levels of economic, organizational and physical scale are needed. One way for LFIs to reach the scale necessary to generate a more significant impact is through increased institutional procurement of local foods. But how do people and organizations come together to generate the social infrastructure required to shift food purchasing practices and processes? This field report shares the story of an innovative community of practice consisting of institutional food buyers, large-scale distributors, regional retailers, processors, producers, researchers, municipal and provincial government representatives within the Edmonton city-region that formed for the express purpose of “creating a positive community impact by getting more local foods on more local plates”. In describing the formation and first three years of the Alberta Flavour Learning Lab we examine the unique characteristics of this community of practice that has aided the development of a common framework for learning, understanding and joint action. In addition to the accomplishments to date, we also discuss the challenges faced by the Learning Lab and the strategies used to overcome them.  

scholarly journals Effect of Mechanical Ventilation on Accidental Hydrogen Releases—Large-Scale Experiments

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3008
Author(s):  
Agnieszka W. Lach ◽  
André V. Gaathaug
Keyword(s):  
Mechanical Ventilation ◽  
Mass Flow ◽  
Large Scale ◽  
Ventilation System ◽  
Hydrogen Gas ◽  
Forced Ventilation ◽  
British Standard ◽  
Confined Spaces ◽  
Series Of Experiments ◽  
Rate Limit

This paper presents a series of experiments on the effectiveness of existing mechanical ventilation systems during accidental hydrogen releases in confined spaces, such as underground garages. The purpose was to find the mass flow rate limit, hence the TPRD diameter limit, that will not require a change in the ventilation system. The experiments were performed in a 40 ft ISO container in Norway, and hydrogen gas was used in all experiments. The forced ventilation system was installed with a standard 315 mm diameter outlet. The ventilation parameters during the investigation were British Standard with 10 ACH and British Standard with 6 ACH. The hydrogen releases were obtained through 0.5 mm and 1 mm nozzles from different hydrogen reservoir pressures. Both types of mass flow, constant and blowdown, were included in the experimental matrix. The analysis of the hydrogen concentration of the created hydrogen cloud in the container shows the influence of the forced ventilation on hydrogen releases, together with TPRD diameter and reservoir pressure. The generated experimental data will be used to validate a CFD model in the next step.

Capacity of prestressed concrete bridge decks under fatigue loading

2021 ◽  
Author(s):  
Eva O. L. Lantsoght ◽  
Cor van der Veen ◽  
Rutger Koekkoek ◽  
Henk Sliedrecht
Keyword(s):  
Prestressed Concrete ◽  
Large Scale ◽  
Fatigue Loading ◽  
Membrane Action ◽  
Variable Amplitude ◽  
Girder Bridges ◽  
Prestressed Girders ◽  
Series Of Experiments ◽  
Prestressed Concrete Bridge ◽  
Compressive Membrane Action

<p>In The Netherlands, existing slab-between-girder bridges with prestressed girders and thin transversely prestressed concrete decks require assessment. The punching capacity was studied in a previous series of experiments, showing a higher capacity thanks to compressive membrane action in the deck. Then, concerns were raised with regard to fatigue loading. To address this, two series of large-scale experiments were carried out, varying the number of loads (single wheel print versus double wheel print), the loading sequence (constant amplitude versus variable amplitude, and different loading sequences for variable amplitude), and the distance between the prestressing ducts. An S-N curve is developed for the assessment of slab-between-girder bridges. The experiments showed that compressive membrane actions enhances the capacity of thin transversely prestressed decks subjected to fatigue loading.</p>

Progressive Evolution of the Core of the Fast Breeder Test Reactor

2010 ◽  
Author(s):  
S. Varatharajan ◽  
K. V. Sureshkumar ◽  
K. V. Kasiviswanathan ◽  
G. Srinivasan
Keyword(s):  
Fast Reactor ◽  
Large Scale ◽  
Power Reactor ◽  
Test Bed ◽  
Fast Breeder Test Reactor ◽  
The Core ◽  
Linear Heat ◽  
Mox Fuel ◽  
Test Reactor ◽  
Carbide Fuel

The second stage of Indian nuclear programme envisages the deployment of fast reactors on a large scale for the effective use of India’s limited uranium reserves. The Fast Breeder Test Reactor (FBTR) at Kalpakkam is a loop type, sodium cooled fast reactor, meant as a test bed for the fuels and structural materials for the Indian fast reactor programme. The reactor was made critical with a unique high plutonium MK-I carbide fuel (70% PuC+30%UC). Being a unique untested fuel of its kind, it was decided to test it as a driver fuel, with conservative limits on Linear Heat Rating and burn-up, based on out-of-pile studies. FBTR went critical in Oct 1985 with a small core of 23 MK-I fuel subassemblies. The Linear Heat Rating and burn-up limits for the fuel were conservatively set at 250 W/cm & 25 GWd/t respectively. Based on out-of-pile simulation in 1994, it was possible to raise the LHR to 320 W/cm. It was decided that when the fuel reaches the target burn-up of 25 GWd/t, the MK-I core would be progressively replaced with a larger core of MK-II carbide fuel (55% PuC+45%UC). Induction of MK-II subassemblies was started in 1996. However, based on the Post-Irradiation Examination (PIE) of the MK-I fuel at 25, 50 & 100 GWd/t, it became possible to enhance the burn-up of the MK-I fuel to 155 GWd/t. More than 900 fuel pins of MK-I composition have reached 155 GWd/t without even a single failure and have been discharged. One subassembly (61 pins) was taken to 165 GWd/t on trial basis, without any clad failure. The core has been progressively enlarged, adding MK-I subassemblies to compensate for the burn-up loss of reactivity and replacement of discharged subassemblies. The induction of MK-II fuel was stopped in 2003. One test subassembly simulating the composition of the MOX fuel (29% PuO2) to be used in the 500 MWe Prototype Fast Breeder Reactor was loaded in 2003. It is undergoing irradiation at 450 W/cm, and has successfully seen a burn-up of 92.5 GWd/t. In 2006, it was proposed to test high Pu MOX fuel (44% PuO2), in order to validate the fabrication and fuel cycle processes developed for the power reactor MOX fuel. Eight MOX subassemblies were loaded in FBTR core in 2007. The current core has 27 MK-I, 13 MK-II, eight high Pu MOX and one power reactor MOX fuel subassemblies. The reactor power has been progressively increased from 10.5 MWt to 18.6 MWt, due to the progressive enlargement of the core. This paper presents the evolution of the core based on the progressive enhancement of the burn-up limit of the unique high Pu carbide fuel.

Performance of Core Exit Thermocouple for PWR Accident Management Action in Vessel Top Break LOCA Simulation Experiment at OECD/NEA ROSA Project

2008 ◽  
Author(s):  
Mitsuhiro Suzuki ◽  
Takeshi Takeda ◽  
Hideo Nakamura
Keyword(s):  
Time Delay ◽  
Large Scale ◽  
Simulation Experiment ◽  
Three Dimensional ◽  
Test Facility ◽  
Large Temperature ◽  
Energy Agency ◽  
Pressurized Water ◽  
The Core ◽  
Accident Management

Presented are experiment results of the Large Scale Test Facility (LSTF) conducted at the Japan Atomic Energy Agency (JAEA) with a focus on core exit thermocouple (CET) performance to detect core overheat during a vessel top break loss-of-coolant accident (LOCA) simulation experiment. The CET temperatures are used to start accident management (AM) action to quickly depressurize steam generator (SG) secondary sides in case of core temperature excursion. Test 6-1 is the first test of the OECD/NEA ROSA Project started in 2005, simulating withdraw of a control rod drive mechanism penetration nozzle at the vessel top head. The break size is equivalent to 1.9% cold leg break. The AM action was initiated when CET temperature rose up to 623K. There was no reflux water fallback onto the CETs during the core heat-up period. The core overheat, however, was detected with a time delay of about 230s. In addition, a large temperature discrepancy was observed between the CETs and the hottest core region. This paper clarifies the reasons of time delay and temperature discrepancy between the CETs and heated core during boil-off including three-dimensional steam flows in the core and core exit. The paper discusses applicability of the LSTF CET performance to pressurized water reactor (PWR) conditions and a possibility of alternative indicators for earlier AM action than in Test 6-1 is studied by using symptom-based plant parameters such as a reactor vessel water level detection.

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