Engineering topics

Huang, C.-H.

Publications and source records attributed to Huang, C.-H..

5 records

DOE OSTI2014

Request for All - A Generalized Request Framework for PhEDEx

PhEDEx has been serving CMS community since 2004 as the data broker. Every PhEDEx operation is initiated by a request, e.g. request to move or to delete data, and so on. A request has it own life cycle, including creation, approval, notification, and book keeping and the details depend on its type. Currently, only two kinds of requests, transfer and deletion, are fully integrated in PhEDEx. They are tailored specifically to the operations' workflows. To be able to serve a new type of request it generally means a fair amount of development work. After several many years of operation, we have gathered enough experience to rethink the request handling in PhEDEx. Generalized Request Project is set to abstract such experience and design a request system which is not tied into current workflow yet it is general enough to accommodate current and future requests. The challenges are dealing with different stages in a request's life cycle, complexity of approval process and complexity of the ability and authority associated with each role in the context of the request. We start with a high level abstraction driven by a deterministic finite automata, followed by a formal description and handling of approval process, followed by a set of tools that make such system friendly to the users. Since we have a formal way to describe the life of a request and a mechanism to systematically handle it, to serve a new kind of request is merely a configuration issue, adding the description of the new request rather than development effort. In this paper, we share the design and implementation of a generalized request framework and the experience of taking an existing serving system through a re-design and re-deployment.

Huang, C.-H.↗

DOE OSTI2014

CMS Space Monitoring

During the first LHC run, CMS stored about one hundred petabytes of data. Storage accounting and monitoring help to meet the challenges of storage management, such as efficient space utilization, fair share between users and groups and resource planning. We present a newly developed CMS space monitoring system based on the storage metadata dumps produced at the sites. The information extracted from the storage dumps is aggregated and uploaded to a central database. A web based data service is provided to retrieve the information for a given time interval and a range of sites, so it can be further aggregated and presented in the desired format. The system has been designed based on the analysis of CMS monitoring requirements and experiences of the other LHC experiments. In this paper, we demonstrate how the existing software components of the CMS data placement system, PhEDEx, have been re-used, dramatically reducing the development effort.

Ratnikova, N.↗

DOE OSTI2014

Re-designing the PhEDEx Security Model

PhEDEx, the data-placement tool used by the CMS experiment at the LHC, was conceived in a more trusting time. The security model provided a safe environment for site agents and operators, but offerred little more protection than that. Data was not sufficiently protected against loss caused by operator error or software bugs or by deliberate manipulation of the database. Operators were given high levels of access to the database, beyond what was actually needed to accomplish their tasks. This exposed them to the risk of suspicion should an incident occur. Multiple implementations of the security model led to difficulties maintaining code, which can lead to degredation of security over time. In order to meet the simultaneous goals of protecting CMS data, protecting the operators from undue exposure to risk, increasing monitoring capabilities and improving maintainability of the security model, the PhEDEx security model was redesigned and re-implemented. Security was moved from the application layer into the database itself, fine-grained access roles were established, and tools and procedures created to control the evolution of the security model over time. In this paper we describe this work, we describe the deployment of the new security model, and we show how these enhancements improve security on several fronts simultaneously.

Huang, C.-H.↗

NASA NTRS2012

Cloud Droplet Size and Liquid Water Path Retrievals From Zenith Radiance Measurements: Examples From the Atmospheric Radiation Measurement Program and the Aerosol Robotic Network

The ground-based Atmospheric Radiation Measurement Program (ARM) and NASA Aerosol Robotic Network (AERONET) routinely monitor clouds using zenith radiances at visible and near-infrared wavelengths. Using the transmittance calculated from such measurements, we have developed a new retrieval method for cloud effective droplet size and conducted extensive tests for non-precipitating liquid water clouds. The underlying principle is to combine a water-absorbing wavelength (i.e. 1640 nm) with a nonwater-absorbing wavelength for acquiring information on cloud droplet size and optical depth. For simulated stratocumulus clouds with liquid water path less than 300 g/sq m and horizontal resolution of 201m, the retrieval method underestimates the mean effective radius by 0.8 m, with a root-mean-squared error of 1.7 m and a relative deviation of 13 %. For actual observations with a liquid water path less than 450 gm.2 at the ARM Oklahoma site during 2007-2008, our 1.5 min-averaged retrievals are generally larger by around 1 m than those from combined ground-based cloud radar and microwave radiometer at a 5min temporal resolution. We also compared our retrievals to those from combined shortwave flux and microwave observations for relatively homogeneous clouds, showing that the bias between these two retrieval sets is negligible, but the error of 2.6 m and the relative deviation of 22% are larger than those found in our simulation case. Finally, the transmittance-based cloud effective droplet radii agree to better than 11% with satellite observations and have a negative bias of 1 m. Overall, the retrieval method provides reasonable cloud effective radius estimates, which can enhance the cloud products of both ARM and AERONET.

Chiu, J. C.↗

NASA NTRS1983

Review of pseudoinverse control for use with kinematically redundant manipulators

Kinematically redundant manipulators have a number of potential advantages over current manipulator designs. For this type of arm, velocity control through pseudoinverses has been suggested. Questions associated with pseudoinverse control are examined in detail and show that in some cases this control leads to undesired arm configurations. A method for distributing joint angles of a redundant arm in a good approximation to a true minimax criterion is described. In addition several numerical considerations are discussed.

Klein, C. A.↗