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Diffusion Compton profondement virtuelle dans le Hall A au Jefferson Laboratory

Description: Generalized Parton Distributions (GPDs), introduced in the late 90s, provide a universal description of hadrons in terms of the underlying degrees of freedom of Quantum Chromodynamics: quarks and gluons. GPDs appear in a wide variety of hard exclusive reactions and the advent of high luminosity accelerator facilities has made the study of GPDs accessible to experiment. Deeply Virtual Compton Scattering (DVCS) is the golden process involving GPDs. The first dedicated DVCS experiment ran in the Hall A of Jefferson Lab in Fall 2004. An electromagnetic calorimeter and a plastic scintillator detector were constructed for this experiment, together with specific electronics and acquisition system. The experiment preparation, data taking and analysis are described in this document. Results on the absolute cross section difference for opposite beam helicities provide the first measurement of a linear combination of GPDs as a function of the momentum transfer to the nucleon.
Date: December 1, 2005
Creator: Camacho, Carlos Munoz
Partner: UNT Libraries Government Documents Department

Biomolecular Assembly of Gold Nanocrystals

Description: Over the past ten years, methods have been developed to construct discrete nanostructures using nanocrystals and biomolecules. While these frequently consist of gold nanocrystals and DNA, semiconductor nanocrystals as well as antibodies and enzymes have also been used. One example of discrete nanostructures is dimers of gold nanocrystals linked together with complementary DNA. This type of nanostructure is also known as a nanocrystal molecule. Discrete nanostructures of this kind have a number of potential applications, from highly parallel self-assembly of electronics components and rapid read-out of DNA computations to biological imaging and a variety of bioassays. My research focused in three main areas. The first area, the refinement of electrophoresis as a purification and characterization method, included application of agarose gel electrophoresis to the purification of discrete gold nanocrystal/DNA conjugates and nanocrystal molecules, as well as development of a more detailed understanding of the hydrodynamic behavior of these materials in gels. The second area, the development of methods for quantitative analysis of transmission electron microscope data, used computer programs written to find pair correlations as well as higher order correlations. With these programs, it is possible to reliably locate and measure nanocrystal molecules in TEM images. The final area of research explored the use of DNA ligase in the formation of nanocrystal molecules. Synthesis of dimers of gold particles linked with a single strand of DNA possible through the use of DNA ligase opens the possibility for amplification of nanostructures in a manner similar to polymerase chain reaction. These three areas are discussed in the context of the work in the Alivisatos group, as well as the field as a whole.
Date: May 20, 2005
Creator: Micheel, Christine Marya
Partner: UNT Libraries Government Documents Department

Fragmentation of quark and gluon jets in proton-antiproton collisions at center-of-mass energy of 1.8-TeV

Description: The author reports the first model independent measurement of charged particle multiplicities in quark and gluon jets, N{sub q} and N{sub g}, produced at the Tevatron in p{bar p} collisions with center-of-mass energy 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies 41 and 53 GeV by counting charged particle tracks in cones with opening angle of {theta}{sub c} = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = E{sub jet}{theta}{sub c} varies in the range from 12 GeV to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = N{sub g}/N{sub q} is found to be 1.64 {+-} 0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with re-summed perturbative QCD calculations and are consistent with recent e{sup +}e{sup -} measurements.
Date: May 1, 2005
Creator: Pronko, Alexandre P. & U., /Florida
Partner: UNT Libraries Government Documents Department

A Globally Distributed System for Job, Data, and Information Handling for High Energy Physics

Description: The computing infrastructures of the modern high energy physics experiments need to address an unprecedented set of requirements. The collaborations consist of hundreds of members from dozens of institutions around the world and the computing power necessary to analyze the data produced surpasses already the capabilities of any single computing center. A software infrastructure capable of seamlessly integrating dozens of computing centers around the world, enabling computing for a large and dynamical group of users, is of fundamental importance for the production of scientific results. Such a computing infrastructure is called a computational grid. The SAM-Grid offers a solution to these problems for CDF and DZero, two of the largest high energy physics experiments in the world, running at Fermilab. The SAM-Grid integrates standard grid middleware, such as Condor-G and the Globus Toolkit, with software developed at Fermilab, organizing the system in three major components: data handling, job handling, and information management. This dissertation presents the challenges and the solutions provided in such a computing infrastructure.
Date: December 1, 2005
Creator: Garzoglio, Gabriele & U., /DePaul
Partner: UNT Libraries Government Documents Department

The Charge asymmetry in W bosons produced in p anti-p collisions at center of mass energy - 1.96 TeV

Description: The primary mode of production of W{sup +} bosons in a p{bar p} collider is u + {bar d} {yields} W{sup +}. The u quark generally carries more momentum than the {bar d} and the resultant W{sup +} tends to be boosted in the proton direction. Similarly, W bosons are boosted in the anti-proton direction. This is observed as an asymmetry in the rapidity distributions of positive and negative W bosons. Measurement of this asymmetry serves as a probe of the momentum distribution of partons within the proton. These distributions are required as input to the calculation of every p{bar p} production cross section. This thesis presents the first measurement at D0 of the charge asymmetry of the W boson production cross section as measured in W {yields} ev decays in 0.3 fb{sup -1} of p{bar p} collisions collected with the D0 Detector. Theoretical predictions made using the CTEQ6.1M and MRST(2004) parton distribution functions are compared with the measurement.
Date: July 1, 2005
Creator: Torborg, Julie M. & U., /Notre Dame
Partner: UNT Libraries Government Documents Department

A Parallel Ocean Model With Adaptive Mesh Refinement Capability For Global Ocean Prediction

Description: An ocean model with adaptive mesh refinement (AMR) capability is presented for simulating ocean circulation on decade time scales. The model closely resembles the LLNL ocean general circulation model with some components incorporated from other well known ocean models when appropriate. Spatial components are discretized using finite differences on a staggered grid where tracer and pressure variables are defined at cell centers and velocities at cell vertices (B-grid). Horizontal motion is modeled explicitly with leapfrog and Euler forward-backward time integration, and vertical motion is modeled semi-implicitly. New AMR strategies are presented for horizontal refinement on a B-grid, leapfrog time integration, and time integration of coupled systems with unequal time steps. These AMR capabilities are added to the LLNL software package SAMRAI (Structured Adaptive Mesh Refinement Application Infrastructure) and validated with standard benchmark tests. The ocean model is built on top of the amended SAMRAI library. The resulting model has the capability to dynamically increase resolution in localized areas of the domain. Limited basin tests are conducted using various refinement criteria and produce convergence trends in the model solution as refinement is increased. Carbon sequestration simulations are performed on decade time scales in domains the size of the North Atlantic and the global ocean. A suggestion is given for refinement criteria in such simulations. AMR predicts maximum pH changes and increases in CO{sub 2} concentration near the injection sites that are virtually unattainable with a uniform high resolution due to extremely long run times. Fine scale details near the injection sites are achieved by AMR with shorter run times than the finest uniform resolution tested despite the need for enhanced parallel performance. The North Atlantic simulations show a reduction in passive tracer errors when AMR is applied instead of a uniform coarse resolution. No dramatic or persistent signs of error growth ...
Date: September 8, 2005
Creator: Herrnstein, A
Partner: UNT Libraries Government Documents Department

Finding the charm in 800 GeV/c p-Cu and p-Be single muon spectra

Description: Fermilab Experiment 866 took single muon data from 800 GeV/c ({radical}s = 38.8 GeV) p-Cu and p-Be interactions in an attempt to extract the inclusive nuclear open charm/anti-charm (D/{bar D}) differential cross sections as a function of p{sub T}. The muons were decay products from semi-leptonic decays of open charm mesons as well as decays from lighter non-charmed mesons ({pi}'s and K's). Data were taken simultaneously from two interaction regions; one of two thin nuclear targets and a copper beam dump 92 inches downstream. The open decay length for hadrons produced in the targets increased the contribution to the muon spectrum from light hadron decays, relative to those from the dump. Production cross sections for light hadrons from previous experiments were used in conjunction with parameterized open charm cross sections to produce total Monte Carlo single muon spectra that were subsequently fit to the data. The sensitivity of this measurement covered an open charm hadron p{sub T} range of approximately 2 to 7 GeV/c, center-of-mass rapidity, y{sub cm}, between 0 and 2, and x{sub F} between 0.2 and 0.8. Previous experimental results for p-p or p-A open charm production at comparable energy was limited to {radical}5 GeV/ Three functions describing the shape of the open charm/anti-charm cross sections were fit to the data; an exponential, A{sub 1} exp (-B p{sub T}), and two polynomials, A{sub 2}/p{sub T}{sup 2} + {alpha}m{sub c}{sup 2}{sup n} and A{sub 2} (1-p{sub T}/p{sub beam}){sup m}/(p{sub T}{sup 2} + {alpha}m{sub c}{sup 2}){sup n}. The first polynomial was fit with the parameter n as a free parameter, and constant with three integer values, 4, 5 and 6. The second was fit with n held fixed at the constant integer values only. The best results were with the first polynomial with n around 6. All three parameterizations resulted ...
Date: January 1, 2005
Creator: Klinksiek, Stephen A. & U., /New Mexico
Partner: UNT Libraries Government Documents Department

Ion Deflection for Final Optics in Laser Inertial Fusion Power Plants

Description: Left unprotected, both transmissive and reflective final optics in a laser-driven inertial fusion power plant would quickly fail from melting, pulsed thermal stress, or degradation of optical properties as a result of ion implantation. One potential option for mitigating this threat is to magnetically deflect the ions such that they are directed to a robust energy dump. In this paper we detail integrated studies that have been carried out to assess the viability of this approach for protecting final optics.
Date: December 12, 2005
Creator: Abbott, R P
Partner: UNT Libraries Government Documents Department

Length-Limited Data Transformation and Compression

Description: Scientific computation is used for the simulation of increasingly complex phenomena, and generates data sets of ever increasing size, often on the order of terabytes. All of this data creates difficulties. Several problems that have been identified are (1) the inability to effectively handle the massive amounts of data created, (2) the inability to get the data off the computer and into storage fast enough, and (3) the inability of a remote user to easily obtain a rendered image of the data resulting from a simulation run. This dissertation presents several techniques that were developed to address these issues. The first is a prototype bin coder based on variable-to-variable length codes. The codes utilized are created through a process of parse tree leaf merging, rather than the common practice of leaf extension. This coder is very fast and its compression efficiency is comparable to other state-of-the-art coders. The second contribution is the Piecewise-Linear Haar (PLHaar) transform, a reversible n-bit to n-bit wavelet-like transform. PLHaar is simple to implement, ideal for environments where transform coefficients must be kept the same size as the original data, and is the only n-bit to n-bit transform suitable for both lossy and lossless coding.
Date: May 17, 2005
Creator: Senecal, J G
Partner: UNT Libraries Government Documents Department

Large Pt processes in ppbar collisions at 2 TeV: measurement of ttbar production cross section in ppbar collisions at s**(1/2) = 1.96 TeV in the dielectron final states at the D0 experiment

Description: The measurement of the top-antitop pair production cross section in p{bar p} collisions at {radical}s = 1.96 TeV in the dielectron decay channel using 384 pb{sup -1} of D0 data yields a t{bar t} production cross-section of {sigma}{sub t{bar t}} = 7.9{sub -3.8}{sup +5.2}(stat){sub -1.0}{sup +1.3}(syst) {+-} 0.5 (lumi) pb. This measurement [98] is based on 5 observed events with a prediction of 1.04 background events. The cross-section corresponds to the top mass of 175 GeV, and is in good agreement with the Standard Model expectation of 6.77 {+-} 0.42 pb based on next-to-next-leading-order (NNLO) perturbative QCD calculations [78]. This analysis shows significant improvement from our previous cross-section measurement in this channel [93] with 230 pb{sup -1} dataset in terms of significantly better signal to background ratio and uncertainties on the measured cross-section. Combination of all the dilepton final states [98] yields a yields a t{bar t} cross-section of {sigma}{sub t{bar t}} = 8.6{sub -2.0}{sup +2.3}(stat){sub -1.0}{sup +1.2}(syst) {+-} 0.6(lumi) pb, which again is in good agreement with theoretical predictions and with measurements in other final states. Hence, these results show no discernible deviation from the Standard Model. Fig. 6.1 shows the summary of cross-section measurements in different final states by the D0 in Run II. This measurement of cross-section in the dilepton channels is the best dilepton result from D0 till date. Previous D0 result based on analysis of 230 pb{sup -1} of data (currently under publication in Physics Letters B) is {sigma}{sub t{bar t}} = 8.6{sub -2.7}{sup +3.2}(stat){sub -1.1}{sup +1.1}(syst) {+-} 0.6(lumi) pb. It can be seen that the present cross-section suffers from less statistical uncertainty. This result is also quite consistent with CDF collaboration's result of {sigma}{sub t{bar t}} = 8.6{sub -2.4}{sup +2.5}(stat){sub -1.1}{sup +1.1}(syst) pb. These results have been presented as D0's preliminary results in the ...
Date: October 1, 2005
Creator: Kumar, Ashish & U., /Delhi
Partner: UNT Libraries Government Documents Department

Measurement of the top - anti-top Production Cross Section at s**(/1/2) = 1.96-TeV in the e + jets Final State of proton anti-proton Collisions at the Tevatron

Description: We discuss the measurement of the cross section for t{bar t} production in p{bar p} collisions at {radical}s = 1.96 TeV in e+jets final states observed at the D0 experiment at the Fermilab Tevatron. Our result is based on data collected from the June 2002 to September 2003 period of Run II of the p{bar p} Collider. In the Standard Model, the top quark is expected to decay mainly into a W boson and a b quark. The W boson can decay subsequently into a lepton and its neutrino or a q{bar q} quark-antiquark pair. In this thesis, we focus on the e{sup +} {nu}{sub e} or e{sup -} {bar {nu}}{sub e} decays of one of the W bosons and the q{bar q} decays of the other W boson in t{bar t} final states. The b, q and q' quarks appear as jets of particles in the detector, thereby defining the e+jets final state. We present two methods used for performing this measurement. The first method is based on a Random Grid Search (RGS) that minimizes the uncertainty on the extracted cross section. The variables used in the search take advantage of differences between expected background and signal processes to obtain the yield of t{bar t} events. The second method uses a Neural Network (NN) procedure that discriminates signal from background through the application of a NN trained on simulated t{bar t} signal and W+jets background events. The preliminary results presented in this thesis for inclusive t{bar t} production are {sigma}{sub p{bar p} {yields} t{bar t} + x} of 7.9{sub -2.4}{sup +2.6}(stat) {sub -2.3}{sup +2.2}(syst) {+-} 0.5 (L) pb for the NN analysis, where the uncertainties correspond to contributions from statistical and systematic sources and from the uncertainty on luminosity. Our measurements are consistent with each other, and are within ...
Date: February 1, 2005
Creator: Cho, DooKee & U., /Rochester
Partner: UNT Libraries Government Documents Department

Measurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton+Jets Final State

Description: The mass of the top quark is a fundamental parameter of the Standard Model. Its precise knowledge yields valuable insights into unresolved phenomena in and beyond the Standard Model. A measurement of the top quark mass with the matrix element method in the lepton+jets final state in D0 Run II is presented. Events are selected requiring an isolated energetic charged lepton (electron or muon), significant missing transverse energy, and exactly four calorimeter jets. For each event, the probabilities to originate from the signal and background processes are calculated based on the measured kinematics, the object resolutions and the respective matrix elements. The jet energy scale is known to be the dominant source of systematic uncertainty. The reference scale for the mass measurement is derived from Monte Carlo events. The matrix element likelihood is defined as a function of both, m{sub top} and jet energy scale JES, where the latter represents a scale factor with respect to the reference scale. The top mass is obtained from a two-dimensional correlated fit, and the likelihood yields both the statistical and jet energy scale uncertainty. Using a dataset of 320 pb{sup -1} of D0 Run II data, the mass of the top quark is measured to be: m{sub top}{sup {ell}+jets} = 169.5 {+-} 4.4(stat. + JES){sub -1.6}{sup +1.7}(syst.) GeV; m{sub top}{sup e+jets} = 168.8 {+-} 6.0(stat. + JES){sub -1.9}{sup +1.9}(syst.) GeV; m{sub top}{sup {mu}+jets} = 172.3 {+-} 9.6(stat.+JES){sub -3.3}{sup +3.4}(syst.) GeV. The jet energy scale measurement in the {ell}+jets sample yields JES = 1.034 {+-} 0.034, suggesting good consistency of the data with the simulation. The measurement forecasts significant improvements to the total top mass uncertainty during Run II before the startup of the LHC, as the data sample will grow by a factor of ten and D0's tracking capabilities will be employed in ...
Date: August 1, 2005
Creator: Schieferdecker, Philipp & U., /Munich
Partner: UNT Libraries Government Documents Department

Measurement of the inclusive bb jet cross section at the Collidor Detector at Fermilab

Description: Data collected by the Fermilab CDF detector are used to measure the inclusive b{bar b} jet production cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. Vertices displaced from the primary interaction point (secondary vertices) are a signature for long-lived decay and are used to identify jets originating from b quarks. An event sample containing two jets, each having an identified secondary vertex, is used. The jets are required to be within the pseudo-rapidity region |{eta}| < 1.2. One of the jets is required to have a transverse energy greater than 30 GeV and the other jet is required to have a transverse energy greater than 20 GeV. The results are compared to Leading Order (Pythia and Herwig) and Next to Leading Order (MC{at}NLO) predictions.
Date: September 1, 2005
Creator: Gajjar, Anant & U., /Liverpool
Partner: UNT Libraries Government Documents Department

Measurement of the w and z cross sections in the electron channel for p anti-p collisions at s**(1/2) = 1.96 TeV and extraction of the w total width from the ratio

Description: This dissertation presents measurements of the inclusive production cross sections for W and Z gauge bosons decaying through the electron channel with p{bar p} collisions at a center-of-mass energy of 1.96 TeV. The ratio of these cross sections is then used to extract the W total width. The Standard Model (SM) of electroweak and strong interactions is a collection of theories which together encompass what is currently known about the elementary particles that make up matter and the forces through which they interact. Experimentalists are constantly searching for violations of the Standard Model by making precision measurements of predicted interactions. The decay of the W boson is one such interaction. The rate of its decay is reflected in its width which is predicted to high precision using Standard Model-based calculations. Therefore, a high precision experimental width measurement would be very sensitive to any such violation. In principle the W and Z boson production cross sections could also be good Standard Model tests. However, a precise knowledge of integrated luminosity is required which is unfortunately difficult to obtain at the Tevatron. In fact, the W and Z cross section results can be used to obtain a more precise luminosity measurement. The data set consists of a total integrated luminosity of 177 pb{sup -1} collected from September 2002 to September 2003 using the D0 detector at Fermilab.
Date: January 1, 2005
Creator: Gardner, John Michael & U., /Kansas
Partner: UNT Libraries Government Documents Department

Measurement of differential cross sections and Cx and Cz for gamma photon-proton going to kaon-lambda baryon and gamma photon-proton going to kaon-sigma baryon using CLAS at Jefferson Lab

Description: This work presents several observables for the reactions γ<italic> p</italic> → <italic>K</italic><super>+</super>Λ and γ<italic> p</italic> → <italic>K</italic><super>+</super>Σ°. In addition to measuring differential cross sections, we have made first measurements of the double polarization observables <italic>C<sub>x</sub></italic> and <italic> C<sub>z</sub></italic>. <italic>C<sub>x</sub></italic> and <italic>C<sub> z</sub></italic> characterize the transfer of polarization from the incident photon to the produced hyperons. Data were obtained at Jefferson Lab using a circularly polarized photon beam at endpoint energies of 2.4, 2.9, and 3.1 GeV. Events were detected with the CLAS spectrometer. In the Λ channel, the cross sections support the recent observation of new resonant structure at <italic>W</italic> = 1900 MeV. Studies of the invariant cross section, <math> <f> <fr><nu>d<g>s</g></nu><de>dd</de></fr></f> </math> show scaling behavior suggesting that the production mechanism becomes <italic> t</italic>-channel dominated near threshold at forward kaon angles. The double polarization observables show that the recoiling Λ is almost maximally polarized along the direction of the incident photon from mid to forward kaon angles. While Σ<super>o</super> differential cross sections are of the same magnitude as the Λ differential cross sections, there is evidence of different physics dominating the production mechanism. The Σ° invariant cross sections do not show the same <italic>t</italic>-scaling behavior present in the Λ results. The double polarization observables indicate that the Σ° is not polarized as strongly as the Λ. They also fail to identify one preferred polarization axis. Complete interpretation of these results will rely on model calculations. Currently available isobar models obtain varying degrees of success while attempting to predict the double polarization observables. While the models are in better agreement with the differential cross sections, discrepancies with our cross sections indicate that they must be re-optimized in light of the new data. While the data suggest that a Regge model would provide a good description of <italic>K</italic><super>+</super>Λ over most of the ...
Date: May 11, 2005
Creator: Bradford, Robert
Partner: UNT Libraries Government Documents Department

Measurement of single spin asymmetry and fifth structure function for the proton(electron vec, electron Kaon+)Lambda reaction with CEBAF Large Acceptance Spectrometer (CLAS)

Description: The single spin asymmetry, A{sub LT} ?, and the polarized structure function, ?{sub LT}?, for the p(e,e?K{sup +})? reaction in the resonance region have been measured and extracted using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Data were taken at an electron beam energy of 2.567 GeV. The large acceptance of CLAS allows for full azimuthal angle coverage over a large range of center-of-mass scattering angles. Results were obtained that span a range in Q{sup 2} from 0.5 to 1.3 GeV{sup 2} and W from threshold up to 2.1 GeV and were compared to existing theoretical calculations. The polarized structure function is sensitive to the interferences between various resonant amplitudes, as well as to resonant and non-resonant amplitudes. This measurement is essential for understanding the structure of nucleons and searching for previously undetected nucleon excited states (resonances) predicted by quark models. The W dependence of the ?{sub LT} ? in the kinematic regions dominated by s and u channel exchange (cos q{sup cm} k = ?0.50, ?0.167, 0.167) indicated possible resonance structures not predicted by theoretical calculations. The ?{sub LT} ? behavior around W = 1.875 GeV could be the signature of a resonance predicted by the quark models and possibly seen in photoproduction. In the very forward angles where the reaction is dominated by the t-channel, the average ?{sub LT} ? was zero. There was no indication of the interference between resonances or resonant and non-resonant amplitudes. This might be indicating the dominance of a single t-channel exchange. Study of the sensitivity of the fifth structure function data to the resonance around 1900 MeV showed that these data were highly sensitive to the various assumptions of the models for the quantum number of this resonance. This project was part of a larger CLAS program to measure cross ...
Date: August 31, 2005
Creator: Nasseripour, Rahksha
Partner: UNT Libraries Government Documents Department

Precision Rosenbluth Measurement of the Proton Elastic Electromagnetic Form Factors and Their Ratio at Q^2=2.64, 3.20, and 4.10 GeV^2

Description: Due to the inconsistency in the results of the mupGEp/GMp ratio of the proton, as extracted from the Rosenbluth and recoil polarization techniques, high precision measurements of the e-p elastic scattering cross sections were made at Q{sup 2} = 2.64, 3.20, and 4.10 GeV{sup 2}. Protons were detected, in contrast to previous measurements where the scattered electrons were detected, which dramatically decreased-dependent systematic uncertainties and corrections. A single spectrometer measured the scattered protons of interest while simultaneous measurements at Q{sup 2} = 0.5 GeV{sup 2} were carried out using another spectrometer which served as a luminosity monitor in order to remove any uncertainties due to beam charge and target density fluctuations. The absolute uncertainty in the measured cross sections is {approx}3% for both spectrometers and with relative uncertainties, random and slope, below 1% for the higher Q{sup 2} protons, and below 1% random and 6% slope for the monitor spectrometer. The extracted electric and magnetic form factors were determined to 4%-7% for GEp and 1.5% for GMp. The ratio mupGEp/GMp was determined to 4%-7% and showed mupGEp/GMp {approx} 1.0. The results of this work are in agreement with the previous Rosenbluth data and inconsistent with high-Q{sup 2} recoil polarization results, implying a systematic difference between the two techniques.
Date: December 1, 2005
Creator: Qattan, Issam A.
Partner: UNT Libraries Government Documents Department