Greatly improved cache update times for conditions data with Frontier/Squid

The CMS detector project loads copies of conditions data to over 100,000 computer cores worldwide by using a software subsystem called Frontier. This subsystem translates database queries into HTTP, looks up the results in a central database at CERN, and caches the results in an industry-standard HTTP proxy/caching server called Squid. One of the most challenging aspects of any cache system is coherency, that is, ensuring that changes made to the underlying data get propagated out to all clients in a timely manner. Recently, the Frontier system was enhanced to drastically reduce the time for changes to be propagated everywhere without heavily loading servers. The propagation time is now as low as 15 minutes for some kinds of data and no more than 60 minutes for the rest of the data. This was accomplished by taking advantage of an HTTP and Squid feature called If-Modified-Since. In order to use this feature, the Frontier server sends a Last-Modified timestamp, but since modification times are not normally tracked by Oracle databases, a PL/SQL program was developed to track the modification times of database tables. We discuss the details of this caching scheme and the obstacles overcome including database and Squid bugs

The CMS DBS Query Language

The CMS experiment has implemented a flexible and powerful system enabling users to find data within the CMS physics data catalog. The Dataset Bookkeeping Service (DBS) comprises a database and the services used to store and access metadata related to CMS physics data. To this, we have added a generalized query system in addition to the existing web and programmatic interfaces to the DBS. This query system is based on a query language that hides the complexity of the underlying database structure by discovering the join conditions between database tables. This provides a way of querying the system that is simple and straightforward for CMS data managers and physicists to use without requiring knowledge of the database tables or keys. The DBS Query Language uses the ANTLR tool to build the input query parser and tokenizer, followed by a query builder that uses a graph representation of the DBS schema to construct the SQL query sent to underlying database. We will describe the design of the query system, provide details of the language components and overview of how this component fits into the overall data discovery system architecture

CMS conditions data access using FroNTier

The CMS experiment at the LHC has established an infrastructure using the FroNTier framework to deliver conditions (i.e. calibration, alignment, etc.) data to processing clients worldwide. FroNTier is a simple web service approach providing client HTTP access to a central database service. The system for CMS has been developed to work with POOL which provides object relational mapping between the C++ clients and various database technologies. Because of the read only nature of the data, Squid proxy caching servers are maintained near clients and these caches provide high performance data access. Several features have been developed to make the system meet the needs of CMS including careful attention to cache coherency with the central database, and low latency loading required for the operation of the online High Level Trigger. The ease of deployment, stability of operation, and high performance make the FroNTier approach well suited to the GRID environment being used for CMS offline, as well as for the online environment used by the CMS High Level Trigger (HLT). The use of standard software, such as Squid and various monitoring tools, make the system reliable, highly configurable and easily maintained. We describe the architecture, software, deployment, performance, monitoring and overall operational experience for the system

Hydrogen storage properties of B- and N-doped microporous carbon

A B- and N-doped microporous carbon has been synthesized via a substitution reaction. The obtained carbon exhibited much higher surface area than the previously reported B- and N-doped carbon. The hydrogen storage measurements indicated that the B- and N-doped microporous carbon had a 53% higher storage capacity than the carbon materials with similar surface areas. Furthermore, hydrogen storage via spillover was studied on Ru-supported B- and N-doped microporous carbon and a storage capacity of 1.2 wt % at 298 K and 10 MPa was obtained, showing an enhancement factor of 2.2. Ab initio molecular orbital calculations were also performed for the binding energies between the spiltover hydrogen atom and various sites on the doped carbon. The theoretical calculations can explain the experimental results well, which also shed light on the most favorable and possible sites with which the spiltover hydrogen atoms bind. © 2009 American Institute of Chemical Engineers AIChE J, 2009Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63091/1/11851_ftp.pd

Hydrogen storage in carbon nanotubes: Residual metal content and pretreatment temperature

Hydrogen storage in MWNT was enhanced via the catalytic activity of NiMgO. The magnitude of the hydrogen to metal ratio for the MWNT/NiMgO system, combined with temperature programmed adsorption and desorption studies, showed hydrogen spillover from the catalyst to the carbon surface. Metal doping combined with temperature activation studies showed that both nickel and magnesium are active in the catalytic process. The yield, quality, and carbon-metal contact were shown to affect hydrogen uptake. Higher pretreatment temperatures enhanced uptake, for both low- and high-pressure measurements, due to increased carbon-metal contact and activation of the catalyst. At 69 bar (or 1,000 psia), the hydrogen adsorption and desorption of the MWNT/NiMgO system were 3.7% and 3.6%, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34249/1/690490619_ftp.pd

Search for Kaluza-Klein Graviton Emission in ppˉp\bar{p} Collisions at s=1.8\sqrt{s}=1.8 TeV using the Missing Energy Signature

We report on a search for direct Kaluza-Klein graviton production in a data sample of 84 ${pb}^{-1}$ of \ppb collisions at $\sqrt{s}$ = 1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and one or two high energy jets. We compare the data with the predictions from a $3+1+n$-dimensional Kaluza-Klein scenario in which gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for $n$=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71 TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure

Ratio of the Isolated Photon Cross Sections at \sqrt{s} = 630 and 1800 GeV

The inclusive cross section for production of isolated photons has been measured in \pbarp collisions at $\sqrt{s} = 630$ GeV with the \D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy ($E_T$) range from 7-49 GeV and have pseudorapidity $|\eta| < 2.5$. This measurement is combined with to previous \D0 result at $\sqrt{s} = 1800$ GeV to form a ratio of the cross sections. Comparison of next-to-leading order QCD with the measured cross section at 630 GeV and ratio of cross sections show satisfactory agreement in most of the $E_T$ range.Comment: 7 pages. Published in Phys. Rev. Lett. 87, 251805, (2001

Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron

We have measured the number of like-sign (LS) and opposite-sign (OS) lepton pairs arising from double semileptonic decays of $b$ and $\bar{b}$-hadrons, pair-produced at the Fermilab Tevatron collider. The data samples were collected with the Collider Detector at Fermilab (CDF) during the 1992-1995 collider run by triggering on the existence of $\mu \mu$ and $e \mu$ candidates in an event. The observed ratio of LS to OS dileptons leads to a measurement of the average time-integrated mixing probability of all produced $b$-flavored hadrons which decay weakly, $\bar{\chi} = 0.152 \pm 0.007$ (stat.) $\pm 0.011$ (syst.), that is significantly larger than the world average $\bar{\chi} = 0.118 \pm 0.005$.Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.

Search for R-parity Violating Supersymmetry in Dimuon and Four-Jets Channel

We present results of a search for R-parity-violating decay of the neutralino chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that this decay proceeds through one of the lepton-number violating couplings lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data, collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at a center of mass energy of 1.8 TeV in 1992-1995.Comment: 10 pages, 3 figure

Spin Correlation in tt-bar Production from pp-bar Collisions at sqrt(s)=1.8 TeV

The D0 collaboration has performed a study of spin correlation in tt-bar production for the process tt-bar to bb-bar W^+W^-, where the W bosons decay to e-nu or mu-nu. A sample of six events was collected during an exposure of the D0 detector to an integrated luminosity of approximately 125 pb^-1 of sqrt{s}=1.8 TeV pp-bar collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the tt-bar decay products. The degree of spin correlation is characterized by a correlation coefficient k. We find that k>-0.25 at the 68% confidence level, in agreement with the SM prediction of k=0.88.Comment: Submitted to PRL, Added references, minor changes to tex