2,825 research outputs found
Optimal Design of a Hexakis Icosahedron Vacuum Based Lighter than Air Vehicle
Due to the rising cost and scarcity of helium, new methods to ensure buoyancy for lighter-than-air vehicles (LTAVs) are being sought. One alternative under study uses an internal vacuum to reduce the weight to buoyancy ratio. It\u27s a novel approach; however, the vacuum presents challenges for the vehicle\u27s structure. The structure must have minimum mass while preventing buckling and excess stress throughout the frame and membrane. The structure under analysis is a hexakis icosahedron with a membrane covering. Achieving minimum mass involves optimizing the structure under the loading conditions. Finite-element analysis (FEA) and direct-search methods are employed, providing an optimal design under various regimes. Specifically, ABAQUS R is used as a FEA modeler, and mesh-adaptive direct search (MADS) is the optimization procedure. The goal of this research is to reduce the diameter of the vehicle using optimization techniques to a goal size of 31 inches (0.7874 meters). The smallest design to date has a diameter of 20 feet (6.096 meters). This research demonstrates the feasibility of two designs, one at 15 feet (4.572 meters) and another at 4 feet (1.2192 meters). The problem formulation includes multiple black-box objectives and constraints. Results for a number of designs are presented and compared
Implementing High Availability with Cots Components and Open-Source Software
High Availability of IT services is essential for the successful operation of large experimental facilities such as the LHC experiments. In the past, high availability was often taken for granted and/or ensured by using very expensive high-end hardware based on proprietary, single-vendor solutions. Today's IT infrastructure in HEP is usually a heterogeneous environment of cheap, off the shelf components which usually have no intrinsic failure tolerance and can thus not be considered reliable at all. Many services, in particular networked services like the Domain Name Service, shared storage and databases need to run on this unreliable hardware, while they are indispensable for the operation of today's control systems. We present our approach to this problem which is based on a combination of open-source tools, such as the Linux High Availability Projet and home-made tools to ensure high-availability for the LHCb Experiment Control system, which consists of over 200 servers, several hundred switches and is controlling thousands of devices ranging from custom made devices, connected to the LAN, to the servers of the event-filter farm
Water vapor lidar
The feasibility was studied of measuring atmospheric water vapor by means of a tunable lidar operated from the space shuttle. The specific method evaluated was differential absorption, a two-color method in which the atmospheric path of interest is traversed by two laser pulses. Results are reported
Rashba spin-orbit coupling in the square lattice Hubbard model: A truncated-unity functional renormalization group study
The Rashba-Hubbard model on the square lattice is the paradigmatic case for studying the effect of spin-orbit coupling, which breaks spin and inversion symmetry, in a correlated electron system. We employ a truncated-unity variant of the functional renormalization group which allows us to analyze magnetic and superconducting instabilities on equal footing. We derive phase diagrams depending on the strengths of Rasbha spin-orbit coupling, real second-neighbor hopping and electron filling. We find commensurate and incommensurate magnetic phases which compete with d-wave superconductivity. Due to the breaking of inversion symmetry, singlet and triplet components mix; we quantify the mixing of d-wave singlet pairing with f-wave triplet pairing
The LHCb experiment control system : on the path to full automation
http://accelconf.web.cern.ch/AccelConf/icalepcs2011/papers/mobaust06.pdfInternational audienceThe experiment control system is in charge of the configuration, control and monitoring of the different subdetectors and of all areas of the online system. The building blocks of the control system are based on the PVSS SCADA System complemented by a control Framework developed in common for the 4 LHC experiments. This framework includes an "expert system" like tool called SMI++ which is used for the system automation. The experiment's operations are now almost completely automated, driven by a top-level object called Big-Brother, which pilots all the experiment's standard procedures and the most common error-recovery procedures. The architecture, tools and mechanisms used for the implementation as well as some operational examples will be described
Analysing multiparticle quantum states
The analysis of multiparticle quantum states is a central problem in quantum
information processing. This task poses several challenges for experimenters
and theoreticians. We give an overview over current problems and possible
solutions concerning systematic errors of quantum devices, the reconstruction
of quantum states, and the analysis of correlations and complexity in
multiparticle density matrices.Comment: 20 pages, 4 figures, prepared for proceedings of the "Quantum
[Un]speakables II" conference (Vienna, 2014
Rank-based model selection for multiple ions quantum tomography
The statistical analysis of measurement data has become a key component of
many quantum engineering experiments. As standard full state tomography becomes
unfeasible for large dimensional quantum systems, one needs to exploit prior
information and the "sparsity" properties of the experimental state in order to
reduce the dimensionality of the estimation problem. In this paper we propose
model selection as a general principle for finding the simplest, or most
parsimonious explanation of the data, by fitting different models and choosing
the estimator with the best trade-off between likelihood fit and model
complexity. We apply two well established model selection methods -- the Akaike
information criterion (AIC) and the Bayesian information criterion (BIC) -- to
models consising of states of fixed rank and datasets such as are currently
produced in multiple ions experiments. We test the performance of AIC and BIC
on randomly chosen low rank states of 4 ions, and study the dependence of the
selected rank with the number of measurement repetitions for one ion states. We
then apply the methods to real data from a 4 ions experiment aimed at creating
a Smolin state of rank 4. The two methods indicate that the optimal model for
describing the data lies between ranks 6 and 9, and the Pearson test
is applied to validate this conclusion. Additionally we find that the mean
square error of the maximum likelihood estimator for pure states is close to
that of the optimal over all possible measurements.Comment: 24 pages, 6 figures, 3 table
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