Oak Ridge K-25 Site Technology Logic Diagram (open access)

Oak Ridge K-25 Site Technology Logic Diagram

The Oak Ridge K-25 Technology Logic Diagram (TLD), a decision support tool for the K-25 Site, was developed to provide a planning document that relates envirorunental restoration and waste management problems at the Oak Ridge K-25 Site to potential technologies that can remediate these problems. The TLD technique identifies the research necessary to develop these technologies to a state that allows for technology transfer and application to waste management, remedial action, and decontamination and decommissioning activities. The TLD consists of four separate volumes-Vol. 1, Vol. 2, Vol. 3A, and Vol. 3B. Volume 1 provides introductory and overview information about the TLD. This volume, Volume 2, contains logic diagrams with an index. Volume 3 has been divided into two separate volumes to facilitate handling and use.
Date: February 26, 1993
Creator: Fellows, R. L. (ed.)
Object Type: Report
System: The UNT Digital Library
Interim report on task 1.4: impurity effects part 2 of 2 appendices to Lawrence Livermore National Laboratory for contract b345772 (open access)

Interim report on task 1.4: impurity effects part 2 of 2 appendices to Lawrence Livermore National Laboratory for contract b345772

None
Date: February 26, 1999
Creator: Stewart, M W A; Vance, E R & Day, R A
Object Type: Report
System: The UNT Digital Library
FY00 LDRD Final Report High Power IFE Driver Component Development 00-SI-009 (open access)

FY00 LDRD Final Report High Power IFE Driver Component Development 00-SI-009

We have begun building the ''Mercury'' laser system as the first in a series of new generation diode-pumped solid-state lasers for target physics research. Mercury will integrate three key technologies: diodes, crystals, and gas cooling, within a unique laser architecture that is scalable to kilojoule and megajoule energy levels for fusion energy applications. The primary near-term performance goals include 10% electrical efficiencies at 10 Hz and 100 J with a 2-10 ns pulse length at 1.047 {micro}m wavelength. Currently, this review concentrates on the critical development and production of Yb:S-FAP crystals. After solving many defect issues that can be present in the crystals, reproducibility is the final issue that needs to be resolved. We have enlisted the help of national experts and have strongly integrated two capable commercial crystal growth companies (Litton-Airton/Synoptics and Scientific Materials) into the effort, and have solicited the advice of Robert Morris (retired from Allied Signal), a recognized international expert in high temperature oxide growth.
Date: February 26, 2001
Creator: Bibeau, C.; Schaffers, K.; Tassano, J.; Waide, P. & Bayramian, A.
Object Type: Report
System: The UNT Digital Library
Speckle Reduction for LIDAR Using Optical Phase Conjugation (open access)

Speckle Reduction for LIDAR Using Optical Phase Conjugation

Remote detection of chemicals using LIDAR (Light Detection and Ranging) utilizing DIAL (Differential Absorption LIDAR) is now a standard detection technique for both military and civilian activities. We have developed a novel nonlinear optical phase conjugation system that can reduce the effects of speckle noise and atmospheric turbulence on DIAL remote detection systems. We have shown numerically and experimentally that it is possible to increase the signal-to-noise (S/N) ratio for LIDAR systems under certain conditions using optical phase conjugation. This increase in S/N can result in more accurate detection of chemical effluents while simultaneously reducing the time necessary to acquire this information.
Date: February 26, 2001
Creator: Bowers, M. W.; Kecy, C.; Little, L.; Cooke, J.; Benterou, J.; Boyd, R. et al.
Object Type: Report
System: The UNT Digital Library
Interim report on task 1.4: impurity effects part 1 of 2 to Lawrence Livermore National Laboratory under contract b345772 (open access)

Interim report on task 1.4: impurity effects part 1 of 2 to Lawrence Livermore National Laboratory under contract b345772

From our work with baseline ceramics containing Pu, or Ce substituted for Pu, doped with sets of inactive impurity ions (with supposedly the same valency) and sintered in different atmospheres, the conclusion is that all ions of similar size and valency are indeed crystal-chemically equivalent unless there are volatility problems. However, the real question appears to be what are the appropriate valency states of the multivalent impurity ions under given sintering conditions. For example, when sintered in highly reducing atmospheres (in this case 3.7 % hydrogen in argon) Mo, W, Zn, Fe, Cu, Co and Ni are reduced to metal. The partitioning across the different phases present is apparently not even. The elements from the nominal 2+, 3+, 4+, 5+ and 6+ families will preferentially move to certain phases or result in the formation of new phases if sufficient amounts are present. If the phases of the baseline ceramic (pyrochlore-zirconolite, brannerite and rutile) are saturated with these ions, new phases will form to take up the excess impurity ions. Additional such phases detected in this work included ulvospinel, perovskite, magnetoplumbite, loveringite-like phases, metallic alloys and powellite/scheelite. The Pu and Ce-doped samples give similar results to each other. While samples sintered …
Date: February 26, 1999
Creator: Stewart, M W A; Vance, E R & Day, R A
Object Type: Report
System: The UNT Digital Library
Determination of the Prebomb Southern (Antartic) Ocean Radiocarbon in Organic Matter (open access)

Determination of the Prebomb Southern (Antartic) Ocean Radiocarbon in Organic Matter

The Southern Hemisphere is an important and unique region of the world's oceans for water-mass formation and mixing, upwelling, nutrient utilization, and carbon export. In fact, one of the primary interests of the oceanographic community is to decipher the climatic record of these processes in the source or sink terms for Southern Ocean surface waters in the CO{sub 2} balance of the atmosphere. Current coupled ocean-atmosphere modeling efforts to trace the input of CO{sub 2} into the ocean imply a strong sink of anthropogenic CO{sub 2} in the southern ocean. However, because of its relative inaccessibility and the difficulty in directly measuring CO{sub 2} fluxes in the Southern Ocean, these results are controversial at best. An accepted diagnostic of the exchange of CO{sub 2} between the atmosphere and ocean is the prebomb distribution of radiocarbon in the ocean and its time-history since atmospheric nuclear testing. Such histories of {sup 14}C in the surface waters of the Southern Ocean do not currently exist, primarily because there are few continuous biological archives (e.g., in corals) such as those that have been used to monitor the {sup 14}C history of the tropics and subtropics. One of the possible long-term archives is the scallop …
Date: February 26, 2001
Creator: Guilderson, T. P.
Object Type: Report
System: The UNT Digital Library
Composition Analysis by Scanned Femtosecond Laser Ultraprobing (CASFLU/DOCMT) (open access)

Composition Analysis by Scanned Femtosecond Laser Ultraprobing (CASFLU/DOCMT)

A new technology for ultrahigh-spatial resolution mapping of the isotopic, molecular, and chemical compositions of complex, multi-dimensional objects, in semiconductor, archaeological, paleontological, biological and materials R&D.
Date: February 26, 2001
Creator: Ishikawa, M. Y.; Armstrong, J. P.; Stuart, B. C.; Wood, L. L. & Wynne, A. E.
Object Type: Report
System: The UNT Digital Library
Development and Demonstration of Insulated Pressure Vessels for Vehicular Hydrogen Storage (open access)

Development and Demonstration of Insulated Pressure Vessels for Vehicular Hydrogen Storage

This paper describes the development of an alternative technology for vehicular storage of hydrogen. Insulated pressure vessels are cryogenic-capable pressure vessels that can accept cryogenic liquid fuel, cryogenic compressed gas or compressed gas at ambient temperature. Insulated pressure vessels offer advantages over alternative hydrogen storage technologies. Insulated pressure vessels are more compact and less expensive than compressed hydrogen vessels. They have lower evaporative losses and lower energy requirement for fuel liquefaction than liquid hydrogen tanks, and they are lighter than hydrides. The work described in this paper is directed at verifying that insulated pressure vessels can be used safely for vehicular hydrogen storage. The paper describes multiple tests and analyses that have been conducted to evaluate the safety of insulated pressure vessels. Insulated pressure vessels have been subjected to multiple DOT, ISO and SAE certification tests, and the vessels have always been successful in meeting the passing criteria for the different tests. A draft procedure for insulated pressure vessel certification has been generated to assist in a future commercialization of this technology. Ongoing work includes the demonstration of this technology in a vehicle.
Date: February 26, 2004
Creator: Berry, G D & Aceves, S M
Object Type: Article
System: The UNT Digital Library
A Comparison of Measured and Calculated Gamma Ray Attenuation for a Common Counting Geometry (open access)

A Comparison of Measured and Calculated Gamma Ray Attenuation for a Common Counting Geometry

In order to perform quantitative gamma spectroscopy, it is necessary to know the sample-specific detection efficiency for photons as a function of energy. The detection efficiency, along with the branching ratio for the isotope and gamma ray of interest, is used to convert observed counts/second to actual disintegrations/second, and, hence, has a large effect on the accuracy of the measurement. In cases where the geometry of the source is simple and reproducible, such as a point source, small vial of solid, or jar of liquid, geometry-specific standards may be counted to determine the detection efficiency. In cases where the samples are large, irregular, or unique, this method generally cannot be used. For example, it is impossible to obtain a NIST-traceable standard glovebox or 55-gallon drum. In these cases, a combination of measured absolute detector efficiency and calculated sample-specific correction factors is commonly used. The correction factors may be calculated via Monte Carlo simulation of the item (the method used by Canberra's ISOCS system), or via semi-empirical calculation of matrix and container attenuations based on the thickness and composition of the container and radioactive matrix (ISOTOPIC by EG&G Ortec uses this method). The accuracy of these correction factors for specific geometries …
Date: February 26, 2004
Creator: Gaylord, R. F.
Object Type: Report
System: The UNT Digital Library
Permeability Enhancement in Fine-Grained Sediments by Chemically Induced Clay Fabric Shrinkage (open access)

Permeability Enhancement in Fine-Grained Sediments by Chemically Induced Clay Fabric Shrinkage

The National Research Council [1] identified the entrapment of contaminants in fine-grained clay-bearing soils as a major impediment to the timely and cost-effective remediation of groundwater to regulatory standards. Contaminants trapped in low-permeability, low-diffusivity, high-sorptivity clays are not accessible to advective flushing by treatment fluids from permeable zones, and slowly diffuse out to recontaminate previously cleaned permeable strata. We propose to overcome this barrier to effective remediation by exploiting the ability of certain nontoxic EPA-approved chemicals (e.g., ethanol) to shrink and alter the fabric of clays, and thereby create macro-porosity and crack networks in fine-grained sediments. This would significantly reduce the distance and time scales of diffusive mass transport to advectively flushed boundaries, to yield orders of magnitude reduction in the time required to complete remediation. Given that effective solutions to this central problem of subsurface remediation do not yet exist, the cost and time benefits of successful deployment of this novel concept, both as a stand-alone technology and as an enabling pre-treatment for other remedial technologies that rely on advective delivery, is likely to be very large. This project, funded as a 1-year feasibility study by LLNL's LDRD Program, is a multi-directorate, multi-disciplinary effort that leverages expertise from the …
Date: February 26, 2004
Creator: Wijesinghe, A. M.; Kansa, E. J.; Viani, B. E.; Blake, R. G.; Roberts, J. J. & Huber, R. D.
Object Type: Report
System: The UNT Digital Library
Development of Nuclear Magnetic Resonance Pulse Sequences and Probes to Study Biomacromolecules (open access)

Development of Nuclear Magnetic Resonance Pulse Sequences and Probes to Study Biomacromolecules

The determination of the three dimensional structures at high resolution of biomolecules, such as proteins and nucleic acids, enables us to understand their function at the molecular level. At the present time, there are only two methods available for determining such structures, nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. Compared to well-established X-ray diffraction techniques, NMR methodology is relatively new and has many areas in which improvement can still be attained. In this project, we focused on the development of new NMR probes and pulse sequences that were tailored to tackle specific problems that are not adequately addressed by current technology. Probes are the hardware that contain the radio frequency (RF) circuitry used to both excite and detect the NMR signals. Pulse sequences are composed of a series of RF pulses and delays, which are applied to the sample held within the magnetic field by the probe, so as to manipulate the nuclear spins. Typically, a probe is developed for a specific set of nuclei and types of experiments and the pulse sequences are then written to use the probe in an optimal manner. In addition, the inter-development of instrumentation and methods are determined by the specific biological question …
Date: February 26, 2001
Creator: Cosman, M; Krishnan, V V & Maxwell, R
Object Type: Report
System: The UNT Digital Library
Laser Damage Inspection Final Report (open access)

Laser Damage Inspection Final Report

Large, high-power laser systems are often designed as reimaging multipass cavities to maximize the extraction of energy from the amplifiers. These multipass cavities often have vacuum spatial filters that suppress the growth of beam instability via B-integral effects. These spatial filters also relay images of laser damage, often nearly superimposing these images in common planes. Also, the fluence damage threshold limits the minimum size of the optics. When used as vacuum barriers in the spatial filters, these large optics present a safety hazard from the risk of implosion if the laser damage were sufficiently large. The objective of the project was to develop algorithms and methods for optical detection and characterization of laser-induced damage of optics. The system should detect small defects (about 5% of the critical size), track their growth over multiple laser shots, and characterize the defects accurately so that the optic can be replaced (at 25% of the critical size) and, hence, minimize the risk of implosion. The depth of field must be short enough to isolate the damaged vacuum barrier from other damaged optics in the beamline, and the system should also be capable of inspecting other optics in the beamline, since damage on one optic …
Date: February 26, 2001
Creator: Salmon, J T; Brase, J M; Bliss, E S; Carrano, C J; Kegelmeyer, L M; Miller, M G et al.
Object Type: Report
System: The UNT Digital Library
Southern California Earthquake Center - SCEC1: Final Report Summary Alternative Earthquake Source Characterization for the Los Angeles Region (open access)

Southern California Earthquake Center - SCEC1: Final Report Summary Alternative Earthquake Source Characterization for the Los Angeles Region

The objective my research has been to synthesize current understanding of the tectonics and faults of the Los Angeles Basin and surrounding region to quantify uncertainty in the characterization of earthquake sources used for geologically- and geodetically-based regional earthquake likelihood models. This work has focused on capturing epistemic uncertainty; i.e. uncertainty stemming from ignorance of the true characteristics of the active faults in the region and of the tectonic forces that drive them. In the present context, epistemic uncertainty has two components: First, the uncertainty in source geometrical and occurrence rate parameters deduced from the limited geological, geophysical and geodetic observations available; and second. uncertainties that result from fundamentally different interpretations of regional tectonic deformation and faulting. Characterization of the large number of active and potentially active faults that need to be included in estimating earthquake occurrence likelihoods for the Los Angeles region requires synthesis and evaluation of large amounts of data and numerous interpretations. This was accomplished primarily through a series of carefully facilitated workshops, smaller meetings involving key researchers, and email groups. The workshops and meetings were made possible by the unique logistical and financial resources available through SCEC, and proved to be extremely effective forums for the …
Date: February 26, 2003
Creator: Foxall, B
Object Type: Report
System: The UNT Digital Library
XFEM: Exploratory Research into the Extended Finite-Element Method, FY02 LDRD Final Report (open access)

XFEM: Exploratory Research into the Extended Finite-Element Method, FY02 LDRD Final Report

This report is one of two components, the first an overview document outlining the goals and results of the XFEM LDRD project, and the other (titled ''Structured Extended Finite Element Methods of Solids defined by Implicit Surfaces'') detailing the scientific advances developed under FY01/FY02 LDRD funding. The XFEM (Extended Finite-Element Method) Engineering LDRD/ER Project was motivated by three research and development goals: (1) the extensions of standard finite-element technology into important new research venues of interest to the Engineering Directorate, (2) the automation of much of the engineering analysis workflow, so as to improve the productivity of mesh-generation and problem setup processes, and (3) the development of scalable software tools to facilitate innovation in XFEM analysis and methods development. The driving principle behind this LDRD project was to demonstrate the computational technology required to perform mechanical analysis of complex solids, with minimal extra effort required on the part of mechanical analysts. This need arises both from the growing workload of LLNL analysts in problem setup and mesh generation, and from the requirement that actual as-built mechanical configurations be analyzed. Many of the most important programmatic drivers for mechanical analysis require that the actual (e.g., deformed, aged, damaged) geometric configuration of …
Date: February 26, 2003
Creator: Mish, K.
Object Type: Report
System: The UNT Digital Library
Spectroscopic Confirmation of A Radio-Selected Galaxy Overdensity at z = 1.11 (open access)

Spectroscopic Confirmation of A Radio-Selected Galaxy Overdensity at z = 1.11

We report the discovery of a galaxy overdensity at z = 1.11 associated with the z = 1.110 high-redshift radio galaxy MG 0442+0202. The group, CL 0442+0202, was found in a near-infrared survey of z > 1 radio galaxies undertaken to identify spatially-coincident regions with a high density of objects red in I - K' color, typical of z > 1 elliptical galaxies. Spectroscopic observations from the Keck I telescope reveal five galaxies within 35'' of MG 0442+0202 at 1.10 < z < 1.11. These member galaxies have broad-band colors and optical spectra consistent with passively-evolving elliptical galaxies formed at high redshift. Archival ROSAT observations reveal a 3{sigma} detection of soft X-ray emission coincident with CL 0442+0202 at a level five times greater than expected for the radio galaxy. These data are suggestive of a rich galaxy cluster and inspired a 45 ks Chandra X-Ray Observatory observation. As expected, the radio galaxy is unresolved to Chandra, but is responsible for approximately half of the observed X-ray flux. The remaining ROSAT flux is resolved into four point sources within 15'' of the radio galaxy, corresponding to a surface density two orders of magnitude higher than average for X-ray sources at these …
Date: February 26, 2004
Creator: Stanford, S; Stern, D; Holden, B & Spinrad, H
Object Type: Article
System: The UNT Digital Library
Study of High Mach Number Laser Driven Blast Waves (open access)

Study of High Mach Number Laser Driven Blast Waves

The study of blast waves produced by intense lasers in gases is motivated by the desire to explore astrophysically relevant hydrodynamic phenomena in the laboratory. We have performed a systematic scan of laser produced blast waves and have examined the blast wave structure over a wide range of drive laser energy. Lasers with energies ranging from 10J-1000J illuminated a pin target in either xenon or nitrogen gas, creating a spherical blast wave. We observe a strongly radiating blast wave in xenon gas while blast waves in nitrogen more closely approximate a pure Taylor-Sedov wave. We also find that at all laser energies, blast waves traveling through xenon gas had their hydrodynamic evolution significantly affected by the passage of the illumination laser.
Date: February 26, 2004
Creator: Edens, A.; Ditmire, T.; Hansen, J. F.; Edwards, M. J.; Adams, R. G.; Rambo, P. et al.
Object Type: Article
System: The UNT Digital Library
Modeling of the Transient Ni-Like Ag X-Ray Laser (open access)

Modeling of the Transient Ni-Like Ag X-Ray Laser

Recent high temporal resolution Ni-like x-ray laser experiments have yielded important insights into the output characteristics of picosecond pumped x-ray lasers. However, current experimental observations do not fully explain the plasma dynamics which are critical to the gain generation within the x-ray laser medium. A theoretical study of the Ni-like Silver x-ray laser has therefore been undertaken to compliment our experimental results, in an attempt to further our understanding of the processes at play in yielding the observed x-ray laser output. Preliminary findings are presented within this paper.
Date: February 26, 2002
Creator: Smith, R.; Benredjem, D.; Moller, C.; Kuba, J.; Klisnick, A.; Pert, G. J. et al.
Object Type: Article
System: The UNT Digital Library
Science & Technology Review April 2003 (open access)

Science & Technology Review April 2003

None
Date: February 26, 2003
Creator: Budil, K
Object Type: Journal/Magazine/Newsletter
System: The UNT Digital Library
Recent X-Ray Laser Characterization Experiments at LLNL (open access)

Recent X-Ray Laser Characterization Experiments at LLNL

We report on a series of experiments, using the COMET picosecond facility, designed to characterize and develop different x-ray laser sources. This work encompasses collisional pumping of slab and gas puff targets.
Date: February 26, 2002
Creator: Smith, R F; Dunn, J; Nilsen, J; Fiedorowicz, H; Bartnik, A. & Shlyaptsev, V N
Object Type: Article
System: The UNT Digital Library
River temperature fluctuation problem (open access)

River temperature fluctuation problem

None
Date: February 26, 1965
Creator: Gustafson, L. D.
Object Type: Report
System: The UNT Digital Library
River contamination reduction studies an evaluation of the artificial lake concept (open access)

River contamination reduction studies an evaluation of the artificial lake concept

Currently the Irradiation Processing Department is working on a program which has as its goal the reduction of radioactive discharge to the Columbia River. The most significant radioactive isotopes of concern are the relatively long lived isotopes P{sup 32}, Zn{sup 65}, As{sup 76}, N{sub p}{sup 239} and Cr{sup 5l}. Because of their relatively long life they can be found in the Columbia River well below the Hanford Plant. P{sup 32}, because it is absorbed and concentrated by the river biota is of prime concern because the dose which it contributes to man through the eating of fish is not known for certain. Included in this reactor effluent decontamination study program are studies of process water recirculation systems, process water pre and post treatment methods, and effluent disposal to an artificial lake. This report reviews the artificial lake concept to determine its feasibility and possible effects on the concentration of radioactive isotopes in the Columbia River downstream of the Hanford Plant. The findings are based on the study and evaluation of available data. Meterological, hydrological, and biological absorption aspects of the artificial lake concept were studied several years ago. Little or no scientific work has been done in recent years to …
Date: February 26, 1962
Creator: unknown
Object Type: Report
System: The UNT Digital Library
Solubility of pllutonium in alkaline salt solutions (open access)

Solubility of pllutonium in alkaline salt solutions

Plutonium solubility data from several studies have been evaluated. For each data set, a predictive model has been developed where appropriate. In addition, a statistical model and corresponding prediction intervals for plutonium solubility as a quadratic function of the hydroxide concentration have been developed. Because of the wide range of solution compositions, the solubility of plutonium can vary by as much as three orders of magnitude for any given hydroxide concentration and still remain within the prediction interval. Any nuclear safety assessments that depend on the maximum amount of plutonium dissolved in alkaline salt solutions should use concentrations at least as great as the upper prediction limits developed in this study. To increase the confidence in the prediction model, it is recommended that additional solubility tests be conducted at low hydroxide concentrations and with all of the other solution components involved. To validate the model for application to actual waste solutions, it is recommended that the plutonium solubilities in actual waste solutions be determined and compared to the values predicted by the quadratic model.
Date: February 26, 1993
Creator: Hobbs, D. T. & Edwards, T. B.
Object Type: Report
System: The UNT Digital Library
An assessment of radiolytic gas generation: Impacts from Rocky Flats Plant residue elimination alternatives. Final report (open access)

An assessment of radiolytic gas generation: Impacts from Rocky Flats Plant residue elimination alternatives. Final report

This report evaluates the Sandia National Laboratory-Albuquerque analytical model that is used to support present wattage limit decisions for various matrix forms from the Residue Elimination Project for Waste Isolation Pilot Plant waste acceptability. This study includes (1) a comparison of the SNL-A model to Rocky Flats Plant models for consistency of assumptions and the phenomena considered in the models, and (2) an evaluation of the appropriateness of the Sandia National Laboratory-Albuquerque model to Rocky Flats Plant residues, considering that the original intent was to model wastes rather than residues. The study draws the following conclusions: (1) only real-time gas generation testing of specific waste streams may provide a sound basis for an increase in the transportation wattage limit of specific waste streams, and (2) the radiolytic gas generation rate from Residue Elimination Project waste emplaced at Waste Isolation Pilot Plant, under worst-case conditions, is not a significant factor in comparison to the total gas generation rate due to radiolysis, microbial degradation, and corrosion.
Date: February 26, 1993
Creator: unknown
Object Type: Report
System: The UNT Digital Library
SRL in-situ tests in the United Kingdom: Part 2, Surface analyses of SRS waste glass buried for one and two years in limestone at Ballidon, UK (open access)

SRL in-situ tests in the United Kingdom: Part 2, Surface analyses of SRS waste glass buried for one and two years in limestone at Ballidon, UK

A multiphase experimental program to assess and understand waste glass behavior under a wide range of conditions has been in progress at the Savannah River Laboratory (SRL) for over a decade. An important part of this experimental effort is to assess the effects of repository relevant conditions on performance of SRS waste glass, in both controlled laboratory tests, as well as in actual field experiments. In laboratory test, SRS waste glass, simulated and in many cases also fully radioactive, has been tested in environments of salt, basalt, shale, granite, clay and tuff. In field experiments, there are four joint international programs being conducted in four different countries, involving burial of SRS simulated waste glass in granite, limestone, clay and salt geologies. This report discusses the SRS waste glass studies in limestone at Ballidon, UK..
Date: February 26, 1991
Creator: Namboodri, C. G. Jr. & Wicks, G. G.
Object Type: Report
System: The UNT Digital Library