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Pushing high-heat-load optics to the limit

Description: A cryogenically cooled silicon monochromator and a water-cooled diamond monochromator have been tested under twice the standard power load conditions at the Advanced Photon Source. Both monochromators performed satisfactorily under these extreme power loads (several hundred watts of incident power and up to 300 W/mm{sup 2} of incident normal peak power density). The experimental data and the parameters derived to predict the performance limits of the cryogenic silicon monochromator are presented.
Date: November 8, 1999
Creator: Fernandez, P. B.
Partner: UNT Libraries Government Documents Department

Silicon bonding techniques for X-ray optics: A summary of R&D work carried out by the Experimental Facilities Division Optics Group (XFD-OP) through July 1995

Description: Some of the most efficient heat-exchanger designs for direct-cooled optics consist of two or more pieces of silicon single crystal bonded to each other and attached to a coolant manifold. Therefore, achieving successful silicon-to-silicon and silicon-to-metal bonds has become one of the goals of the high heat load (HHL) optics program. A viable bond for a cooled silicon optic has to satisfy the following requirements: strain free; compatible with the coolant used; radiation resistant; coefficient of thermal expansion of the bonding agent must be close to that of silicon. The techniques that have been pursued by XFD-OP members are: Si-Si direct bonding; Si-Si die attach paste bonding; Si-Si and Si-metal epoxy bonding; Si-Si and Si-metal glass frit bonding; and Si-metal gold-based solder. A description of each of these techniques and their performance are described in this report.
Date: August 31, 1995
Creator: Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Feasibility of using a high power CO{sub 2} laser as an alternative source to test high heat load x-ray optics

Description: To determine the feasibility of using the CO{sub 2} laser at LAL as an alternative heat source for x-ray optics tests, we have studied the absorption of the 10.6-micron laser light in silicon for two different dopant concentrations, using the resistivity as a predictor for the absorption length. We describe the results from these tests in this report.
Date: May 10, 1993
Creator: Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Asymmetric-cut monochromator with adjustable asymmetry

Description: A variable incident angle, asymmetric cut, double crystal monochromator was tested for use on beamlines at the Advanced Photon Source (APS). For both undulator and wiggler beams the monochromator can expand area of footprint of beam on surface of the crystals to 50 times the area of incident beam; this will reduce the slope errors by a factor of 2500. The asymmetric cut allows one to increase the acceptance angle for incident radiation and obtain a better match to the opening angle of the incident beam. This can increase intensity of the diffracted beam by a factor of 2 to 5 and can make the beam more monochromatic, as well. The monochromator consists of two matched, asymmetric cut (18 degrees), silicon crystals mounted so that they can be rotated about three independent axes. Rotation around the first axis controls the Bragg angle. The second rotation axis is perpendicular to the diffraction planes and controls the increase of the area of the footprint of the beam on the crystal surface. Rotation around the third axis controls the angle between the surface of the crystal and the wider, horizontal axis for the beam and can make the footprint a rectangle with a minimum. length for this area. The asymmetric cut is 18 degrees for the matched pair of crystals, which allows one to expand the footprint area by a factor of 50 for Bragg angles up to 19.15 degrees (6 keV for Si[111] planes). This monochromator, with proper cooling, will be useful for analyzing the high intensity x-ray beams produced by both undulators and wigglers at the APS.
Date: January 1, 1993
Creator: Smither, R.K. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Further tests on liquid-nitrogen-cooled, thin silicon-crystal monochcromators using a focused wiggler synchrotron beam

Description: A newly designed, cryogenically cooled, thin Si crystal monochromator was tested at the European Synchrotron Radiation Facility (ESRF) beamline BL3. It exhibited less than 1 arcsec of thermal strain up to a maximum incident power of 186 W and average power density of 521 W/mm{sup 2}. Data were collected for the thin (0.7 mm) portion of the crystal and for the thick (>25 mm) part. Rocking curves were measured as a function of incident power. With a low power beam, the Si(333) rocking curve at 30 keV for the thin and thick sections was < 1 arcsec FWHM at room temperature. The rocking curve of the thin section increased to 2.0 arcsec when cooled to 78 K, while the thick part was unaffected by the reduction in temperature. The rocking curve of the thin section broadened to 2.5 arcsec FWHM and that of the thick section broadened to 1.7 arcsec at the highest incident power. The proven range of performance for this monochromator has been extended to the power density, but not the absorbed power, expected for the Advanced Photon Source (APS) undulator A in closed-gap operation (first harmonic at 3.27 keV) at a storage-ring current of 300 mA.
Date: January 1, 1996
Creator: Rogers, C.S.; Mills, D.M. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Advanced photon source undulator beamline tests of a contact-cooled silicon u-shaped monochromator

Description: At the Advanced Photon Source (APS), undulator insertion devices are capable of producing x-ray beams with total power of about 5 kW and normal incidence heat fluxes of about 170 W/mm{sup 2} at 30 m from the source. On beamlines in which the first optical element is a mirror, the reflected beam from the mirror still carries considerable power and power density. Depending on its location, the monochromator downstream of the mirror might be subject to 300 W total power and 5 W/mm{sup 2} normal incidence heat flux. Thus, it is still necessary to carefully design a monochromator that provides acceptable performance under these heat loads. A contact-cooled u-shaped monochromator may be used in this case. The main feature of the u-shaped monochromator is that, by carefully selecting the geometry and cooling locations, is passively corrects for some of the thermally induced crystal distortions. We present experimental and computational results of a contact cooled u-shaped monochromator tested on an APS undulator beamline. The results are encouraging and compare favorably with liquid-gallium internally cooled crystals.
Date: September 1, 1997
Creator: Lee, W.K.; Fernandez, P.B. & Khounsary, A.
Partner: UNT Libraries Government Documents Department

Progress in silicon-to-silicon direct bonding and its application to synchrotron x-ray optics

Description: X-ray optical elements (such as single-crystal silicon monochromators) illuminated with high-power synchrotron-radiation beams produced by insertion devices and, to a lesser extent bending magnets, require cooling, When operating a silicon crystal at room temperature, channels for the coolant are often fabricated directly beneath the diffracting surface. Then a separate silicon distribution manifold/plenum is manufactured, and the components are bonded together using an adhesive or some intermediate material. In many cases, such monochromators suffer from strains induced by the bond. A silicon-to-silicon direct-bonding technique (i.e., without any intermediate material) has been developed that appears to be an attractive method for creating a bond with less strain between two pieces of silicon. This technique is well understood for the case of thin wafers ({approximately}0.5 mm thickness) and is used by the semiconductor industry. Recently, bonding of 16-mm-thick 10-cm-diameter silicon crystals has been successfully performed inducing very little strain. A short review of the silicon-to-silicon crystals has been successfully performed inducing very little strain. A short review of the silicon-to-silicon direct-bonding process will be presented with an emphasis on its application to room temperature high-heat-load x-ray optics with the present status of direct bonding efforts at the APS.
Date: February 1, 1997
Creator: Graber, T.; Krasnicki, S. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

High-heat-load synchrotron tests of room-temperature, silicon crystal monochromators at the CHESS F-2 wiggler station

Description: This note summarizes the results of the single crystal monochromator high-heat-load tests performed at the CHESS F-2 wiggler station. The results from two different cooling geometries are presented: (1) the ``pin-post`` crystal and (2) the ``criss-cross`` crystal. The data presented were taken in August 1993 (water-cooled pin-post) and in April 1995 (water- and gallium-cooled pin-post crystal and gallium-cooled criss-cross crystal). The motivation for trying these cooling (or heat exchanger) geometries is to improve the heat transfer efficiency over that of the conventional slotted crystals. Calculations suggest that the pin-post or the microchannel design can significantly improve the thermal performance of the crystal. The pin-post crystal used here was fabricated by Rocketdyne Albuquerque Operations. From the performance of the conventional slotted crystals, it was thought that increased turbulence in the flow pattern may also enhance the heat transfer. The criss-cross crystal was a simple attempt to achieve the increased flow turbulence. The criss-cross crystal was partly fabricated in-house (cutting, etching and polishing) and bonded by RAO. Finally, a performance comparison among all the different room temperature silicon monochromators that have been tested by the APS is presented. The data includes measurements with the slotted crystal and the core-drilled crystals. Altogether, the data presented here were taken at the CHESS F-2 wiggler station between 1991 and 1995.
Date: September 8, 1995
Creator: Lee, W.K.; Fernandez, P.B.; Graber, T. & Assoufid, L.
Partner: UNT Libraries Government Documents Department

High-heat-load studies of silicon and diamond monochromators using the APS/CHESS prototype undulator

Description: The results of the latest high-heat-load studies made on the APS/CHESS prototype undulator are summarized. Four different crystals were tested: two slotted, symmetrically cut silicon crystals and a core-drilled, asymmetrically cut silicon crystal and a diamond crystal that was jet cooled using water. The purpose of the silicon crystal tests was to reevaluate the surface power loading at which appreciable degradation of the diffraction efficiency was observed. The diamond tests, allotted only a brief period of time during the testing period, were our first attempt at using diamonds for high-heat-flux x-ray monochromators and were performed primarily to gain first-hand experience with diamond monochromators. Measurements with the silicon crystal at 5 keV reconfirmed our previous measurements of performance degradation at around 4-6 watts/mm{sup 2} using liquid gallium with slotted coolant channels. A value of only 2 watts/mm{sup 2} was observed to cause a degradation of the diffraction performance at 15 keV with the same crystals due to the increased sensitivity to strain because of the reduced Darwin widths. The performance of the asymmetric crystal, with its core-drilled coolant channels, was not found to be as good as that of the slotted crystals. This was probably due to poorer heat transfer properties of the core-drilled geometry in combination with the narrowing of the rocking curves because of the asymmetric cut. Fabrication issues for construction of the gallium-cooled crystals is also discussed. Although the diamonds were only successfully tested at low total power the results were very encouraging and motivated us to accelerate our program on the use of diamonds for high-heat-load monochromators.
Date: September 16, 1994
Creator: Mills, D.M.; Lee, W.K.; Smither, R.K. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Apparent temperature versus true temperature of silicon crystals as a function of their thickness using infrared measurements

Description: The very high intensity x-ray beams that will be present at the Advanced Photon Source and other third generation synchrotron sources will require that the first optical element in the beamline and, possibly, the second optical element as well, be cooled to remove the heat deposited by the x-ray beam. In many of the beamlines this heat will be in the 1 to 5 kW range, and any failure of the cooling system will require a quick response from safety control circuits to shut off the beam before damage is done to the optical element. In many cases, this first optical element will be a silicon diffraction crystal. Viewing the surface of objects subjected to high heat fluxes with an infrared camera or infrared sensor has proved to be a very effective method for monitoring the magnitude and distribution of surface temperatures on the object. This approach has been quite useful in studies of cooling silicon crystals in monochromators subject to high heat loads. The main drawback to this method is that single crystals of silicon are partially transparent to the infrared radiation monitored in most infrared cameras. This means that the infrared radiation emitted from the surface contains a component that comes from the interior of the crystal and that the intensity of the emitted radiation and thus the apparent temperature of the surface of the crystal depends on the thickness of the crystal and the kind of coating on the back (and/or the front) of the crystal. The apparent temperature of the crystal increases as the crystal is made thicker. A series of experiments were performed at Argonne National Laboratory to calibrate the apparent surface temperature of the crystal as measured with an infrared camera as a function of the crystal thickness and the type of coating (if ...
Date: December 31, 1993
Creator: Smither, R. K. & Fernandez, P. B.
Partner: UNT Libraries Government Documents Department

Brilliance and flux reduction in imperfect inclined crystals

Description: The inclined crystal geometry has been suggested as a method of reducing the surface absorbed power density of high-heat-load monochromators for third-generation synchrotron radiation sources. Computer simulations have shown that if the crystals are perfectly aligned and have no strains then the diffraction properties of a pair of inclined crystals are very similar to a pair of conventional flat crystals with only subtle effects differentiating the two configurations. However, if the crystals are strained, these subtle differences in the behavior of inclined crystals can result in large beam divergences causing brilliance and flux losses. This manuscript elaborates on these issues and estimates potential brilliance and flux losses from strained inclined crystals at the APS.
Date: January 1, 1996
Creator: Lee, W.K.; Blasdell, R.C.; Fernandez, P.B.; Macrander, A.T. & Mills, D.M.
Partner: UNT Libraries Government Documents Department

Experimental results with cryogenically cooled, thin, silicon crystal x-ray monochromators on high-heat-flux beamlines

Description: A novel, silicon crystal monochromator has been designed and tested for use on undulator and focused wiggler beamlines at third-generation synchrotron sources. The crystal utilizes a thin, partially transmitting diffracting element fabricated within a liquid-nitrogen cooled, monolithic block of silicon. This report summarizes the results from performance tests conducted at the European Synchrotron Radiation Facility (ESRF) using a focused wiggler beam and at the Advanced Photon Source (APS) on an undulator beamline. These experiments indicate that a cryogenic crystal can handle the very high power and power density x-ray beams of modem synchrotrons with sub-arcsec thermal broadening of the rocking curve. The peak power density absorbed on the surface of the crystal at the ESRF exceeded go W/mm{sup 2} with an absorbed power of 166 W, this takes into account the spreading of the beam due to the Bragg angle of 11.4{degrees}. At the APS, the peak heat flux incident on the crystal was 1.5 W/mA/mm{sup 2} with a power of 6.1 W/mA for a 2.0 H x 2.5 V mm{sup 2} beam at an undulator gap of 11.1 mm and stored current up to 96 mA.
Date: August 1, 1996
Creator: Rogers, C.S.; Mills, D.M.; Lee, W.K.; Fernandez, P.B. & Graber, T.
Partner: UNT Libraries Government Documents Department

Test results of a diamond double-crystal monochromator at the advanced photon source

Description: We have tested the first diamond double-crystal monochromator at the Advanced Photon Source (APS). The monochromator consisted of two synthetic type lb (111) diamond plates in symmetric Bragg geometry. We tested two pairs of single-crystal plates: the first pair was 6 mm by 5 mm by 0.25 mm and 6 mm by 5 mm by 0.37 mm; the second set was 7 mm by 5.5 mm by 0.44 mm. The monochromator first crystal was indirectly cooled by edge contact with a water-cooled copper holder. We studied the performance of the monochromator under the high-power x-ray beam delivered by the APS undulator A. We found no indication of thermal distortions or strains even at the highest incident power (280 watts) and power density (123 W/mm{sup 2} at normal incidence). The calculated maximum power and power density absorbed by the first crystal were 37 watts and 16 W/mm{sup 2} respectively. We also compared the maximum intensity delivered by the diamond monochromator and by a silicon (111) cryogenically cooled monochromator. For energies in the range of 6 to 10 keV, the flux through the diamond monochromator was about a factor of two less than through the silicon monochromator, in good agreement with calculations. We conclude that water-cooled diamond monochromators can handle the high-power beams from the undulator beams from the undulator beamlines at the APS. As single-crystal diamond plates of larger size and better quality become available, the use of diamond monochromators will become a very attractive option.
Date: June 1, 1997
Creator: Fernandez, P.B.; Graber, T.; Krasnicki, S. & Lee, W.K.
Partner: UNT Libraries Government Documents Department

A tunable crystal diffraction telescope for the International Space Station

Description: Even though technically innovative, a tunable crystal diffraction telescope for use in nuclear astrophysics has become feasible today. The focusing gamma-ray telescope the authors intended to propose for the space station consists of a tunable crystal diffraction lens, focusing gamma-rays onto a small array of Germanium detectors perched on an extendible boom. While the weight of such an instrument is less than 500 kg, it features an angular resolution of 15 inches, an energy resolution of 2 keV and a 3 {sigma} sensitivity of a few times 10{sup {minus}7} photons{center_dot}s{sup {minus}1}{center_dot}cm{sup {minus}2} (10{sup 6} sec observation) for any individual narrow line at energies between 200--1,300 keV. This experience would greatly profit from the continuous presence of man on the station. Besides of the infrastructure for maintenance and servicing of the various innovative techniques used for the first time in space, the available extra-vehicular robotics will facilitate deployment of the required boom structure.
Date: February 1, 1997
Creator: Ballmoos, P. von; Kohnle, A.; Olive, J.F.; Vedrenne, G.; Smither, R.K.; Fernandez, P.B. et al.
Partner: UNT Libraries Government Documents Department

Crystal diffraction lens telescope for focusing nuclear gamma rays

Description: A crystal diffraction lens was constructed at Argonne National Laboratory for use as a telescope to focus nuclear gamma rays. It consisted of 600 single crystals of germanium arranged in 8 concentric rings. The mounted angle of each crystal was adjusted to intercept and diffract the incoming gamma rays with an accuracy of a few arc sec. The performance of the lens was tested in two ways. In one case, the gamma rays were focused on a single medium size germanium detector. In the second case, the gamma rays were focused on the central germanium detector of a 3 x 3 matrix of small germanium detectors. The efficiency, image concentration and image quality, and shape were measured. The tests performed with the 3 x 3 matrix detector system were particularly interesting. The wanted radiation was concentrated in the central detector. The 8 other detectors were used to detect the Compton scattered radiation, and their energy was summed with coincident events in the central detector. This resulted in a detector with the efficiency of a large detector (all 9 elements) and the background of a small detector (only the central element). The use of the 3 x 3 detector matrix makes it possible to tell if the source is off axis and, if so, to tell in which direction. The crystal lens acts very much like a simple convex lens for visible light. Thus if the source is off to the left then the image will focus off to the right illuminating the detector on the right side: telling one in which direction to point the telescope. Possible applications of this type of crystal lens to balloon and satellite experiments will be discussed.
Date: August 1, 1996
Creator: Smither, R.K.; Fernandez, P.B.; Graber, T.; Ballmoos, P. von; Naya, J.; Albernhe, F. et al.
Partner: UNT Libraries Government Documents Department

Further tests on liquid-nitrogen-cooled, thin silicon-crystal monochromators using a focused wiggler synchrotron beam

Description: A newly designed cryogenically cooled, thin Si crystal monochromator was tested at the European Synchrotrons Radiation Facility (ESRF) beamline BL3. It exhibited less than 1 arcsec of thermal strain up to a maximum incident power of 186 W and average power density of 521 W/mm{sup 2}. Data were collected for the thin (0.7 mm) portion of the crystal and for the thick (&gt;25 mm) part. Rocking curves were measured as a function of incident power. With a low power beam, the Si(333) rocking curve at 30 keV for the thin and thick sections was &lt; 1 arcsec FWHM at room temperature. The rocking curve of the thin section increased to 2.0 arcsec when cooled to 78 K, while the thick part was unaffected by the reduction in temperature. The rocking curve of the this section broadened to 2.5 arcsec FWHM and that of the thick section broadened to 1.7 arcsec at the highest incident power. The proven range of performance for this monochromator has been extended to the power density, but not the absorbed power, expected for the Advanced Photon Source (APS) undulator A in closed-gap operation (first harmonic at 3.27 kev) at a storage-ring current of 300 mA.
Date: May 9, 2000
Creator: Rogers, C. S.; Mills, D. M.; Fernandez, P. B.; Knapp, G. S.; Wulff, M.; Hanfland, M. et al.
Partner: UNT Libraries Government Documents Department

Experimental results obtained with the positron-annihilation- radiation telescope of the Toulouse-Argonne collaboration

Description: We present laboratory measurements obtained with a ground-based prototype of a focusing positron-annihilation-radiation telescope developed by the Toulouse-Argonne collaboration. This balloon-borne telescope has been designed to collect 511-keV photons with an extremely low instrumental background. The telescope features a Laue diffraction lens and a detector module containing a small array of germanium detectors. It will provide a combination of high spatial and energy resolution (15 arc sec and 2 keV, respectively) with a sensitivity of {approximately}3{times}10{sup {minus}5} photons cm{sup {minus}2}s{sup {minus}1}. These features will allow us to resolve a possible narrow 511-keV line both energetically and spatially within a Galactic center ``microquasar`` or in other broad-class annihilators. The ground-based prototype consists of a crystal lens holding small cubes of diffracting germanium crystals and a 3{times}3 germanium array that detects the concentrated beam in the focal plane. Measured performances of the instrument at different line energies (511 keV and 662 keV) are presented and compared with Monte-Carlo simulations. The advantages of a 3{times}3 Ge-detector array with respect to a standard-monoblock detector have been confirmed. The results obtained in the laboratory have strengthened interest in a crystal-diffraction telescope, offering new perspectives for die future of experimental gamma-ray astronomy.
Date: October 1, 1995
Creator: Naya, J.E.; von Ballmoos, P.; Albernhe, F.; Vedrenne, G.; Smither, R.K.; Faiz, M. et al.
Partner: UNT Libraries Government Documents Department

Review of crystal diffraction and its application to focusing energetic gamma rays

Description: The basic features of crystal diffraction and their application to the construction of a crystal diffraction lens for focusing energetic gamma rays are described using examples from the work preformed at the Argonne National Laboratory. Both on-axis and off-axis performance are discussed. The review includes of normal crystals, bent crystals, and crystals with variable crystal-plane spacings to develop both condenser-type lenses and point-to-point imaging lenses.
Date: October 1, 1995
Creator: Smither, R.K.; Fernandez, P.B.; Graber, T.; von Ballmoos, P.; Naya, J.; Albernhe, F. et al.
Partner: UNT Libraries Government Documents Department

Proton-induced fission at ultra sub-barrier energies

Description: Cross sections for proton-induced fission of {sup 238}U have been measured at seven proton energies ranging from 3.0 to 4.45 MeV using two position sensitive parallel-grid avalanche counters in a kinematic coincidence. In addition, an upper limit for the fission cross section was established at extreme sub-barrier energies down to a level of {approx equal}20 pb at 3 MeV. This result is in contradiction to recent findings of Ajitanand et al., who found that the fission excitation function exhibited a plateaux at about 1000 pb in the energy range from 1.0 to 3.5 MeV. 7 refs., 3 figs., 1 tab.
Date: January 1, 1991
Creator: Back, B.B.; Betts, R.R.; Fernandez, P.B.; Gehring, J.C.; Henderson, D.J. & Nagame, Y.
Partner: UNT Libraries Government Documents Department

The Hg region: Superdeformation and other shapes

Description: We shall first summarize the present experimental situation concerning {sup 192}Hg, the nucleus regarded as the analog of {sup 152}Dy{sup 8} for this SD region in that shell gaps are calculated {sup 5} to occur at large deformation for Z=80 and N=112. Proton and neutron excitations out of te {sup 192}Hg core will then be reviewed with particular emphasis on {sup 191}Hg and {sup 193}Tl. The implications of the results for pairing at large deformations and the need to consider other degrees of freedom (such as octupole correlations) will be addressed. The presentation will conclude with a brief discussion on other shapes seen in this region, with a particular emphasis on {sup 191}Hg.
Date: January 1, 1990
Creator: Janssens, R.V.F.; Carpenter, M.P.; Fernandez, P.B.; Moore, E.F.; Ahmad, I.; Khoo, T.L. et al.
Partner: UNT Libraries Government Documents Department

Superdeformation in the mercury nuclei

Description: We shall first summarize the present experimental situation concerning {sup 192}Hg, the nucleus regarded as the analog of {sup 152}Dy for this superdeformation (SD) region in that gaps are calculated to occur at large deformation for Z = 80 and N = 112. Proton and neutron excitations out of the {sup 192}Hg core will then be reviewed with particular emphasis on {sup 191}Hg and {sup 193}Tl. The presentation will conclude with a brief discussion on limits of the SD region for neutron deficient Hg nuclei. 26 refs., 10 figs.
Date: January 1, 1990
Creator: Janssens, R.V.F.; Carpenter, M.P.; Fernandez, P.B.; Moore, E.F.; Ahmad, I.; Khoo, T.L. et al.
Partner: UNT Libraries Government Documents Department

Feeding and decay of superdeformed states

Description: The mechanisms for feeding and decay of superdeformed (SD) bands are examined. Data connected with both processes in [sup 192]Hg are compared with model calculations. The calculations successfully reproduce the data, suggesting that the mechanisms for both processes are understood. Constraints on the energy of the SD band energies and on the well-depths at low and high spins have been obtained. At the point of decay around spin 10, we suggest that the SD band is 3.3--4.3 MeV above the normal yrast line and that the well depths at spin 10 and 40 are 0.5--1.3 and 3.5--4.5 MeV, respectively.
Date: January 1, 1992
Creator: Khoo, T.L.; Lauritsen, T.; Ahmad, I.; Carpenter, M.P.; Fernandez, P.B.; Janssens, R.V.F. et al.
Partner: UNT Libraries Government Documents Department