Effects of pressure on spin fluctuations and the exchange interaction in La2CuO4 as determined by two‐magnon Raman scattering (abstract)

We have measured the two‐magnon Raman scattering spectrum of magnetic La2CuO4 at pressures of up to 100 kbar. Analysis of the moments of the two‐magnon line shape indicates that the renormalization parameters resulting from spin fluctuations are essentially pressure independent in this pressure range. Our results provide the first direct determination of the pressure dependence of the in‐plane exchange coupling constant J. The pressure dependence of J is compared with that of the Néel temperature and discussed in the context of recent theories for quasi‐two‐dimensional magnetic systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71024/2/JAPIAU-69-8-5392-1.pd

Lithium metal for x-ray refractive optics

Lithium metal is the best material for refractive lenses that must focus x-rays with energies below 15 keV, but to date no lens from Li has been reported. This letter demonstrates focusing of 10 keV x-rays with a one-dimensional sawtooth lens made from Li. The lens’ theoretical gain is 4.5, with manufacturing imperfections likely responsible for the threefold gain that is observed. Despite the Li reactivity the lens is stable over months of operation if kept under vacuum. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69644/2/APPLAB-79-25-4085-1.pd

Design and performance of a stable first crystal mount for a cryogenically cooled Si monochromator at the Advanced Photon Source

We present a new design for mounting a cryogenically cooled Si crystal which gives greatly improved beam stability. The design has been successfully implemented at the University of Michigan, Howard University, Bell Laboratories-Lucent Technologies Collaborative Access Team (MHATT-CAT) 7ID Beamline of the Advanced Photon Source. Before the installation of the new crystal mount, our Si (lll) cryogenically cooled monochromator was sensitive to the pressure fluctuations of the liquid nitrogen coolant, such that the angle of incidence on the first crystal varied linearly with the applied pressure in the cooling lines, causing beam motion of about 250 μm, 60 m250μm,60m from the source. The key element of the design is a symmetrically positioned cooling manifold which balances the forces caused by pressure fluctuations. With this new mount, the typical beam stability is now about 10 μm, comparable to the source stability. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69891/2/RSINAK-73-3-1511-1.pd

Asymmetrically cut crystals as optical elements for highly collimated x‐ray beams

Asymmetrically cut perfect crystals, in both the Laue and Bragg geometries, are examined as single crystal monochromators for x‐ray beams that are collimated to a small fraction of the Darwin width, as is typical in experiments with coherent x rays. Both the Laue and asymmetric Bragg geometries are plagued by an inherent chromatic aberration that increases the beam divergence much beyond that of the symmetric Bragg geometry. Measurements from a recent experiment at the ESRF are presented to compare Si(220) (symmetric Bragg), diamond(111) (asymmetric Laue), and diamond(111) (symmetric Bragg inclined) geometries. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70952/2/RSINAK-66-2-1506-1.pd

Performance of the double multilayer monochromator on the NSLS wiggler beam line X25

A tunable, double multilayer x-ray monochromator has recently been implemented on the National Synchrotron Light Source (NSLS) X25 wiggler beam line. It is based on a parallel pair of tungsten-boron-carbide multilayer films grown on silicon substrates and purchased from Osmic, Inc. of Troy, Michigan, USA. It acts as an optional alternative to the conventional double silicon crystal monochromator, and uses the same alignment mechanism. Two other NSLS beam lines also have had this kind of monochromator installed recently, following the lead of the NSLS X20C IBM/MIT beam line which has used a double multilayer monochromator for several years. Owing to the 100 times broader bandwidth of a multilayer x-ray monochromator, compared with a silicon monochromator, the multilayer monochromator has the obvious advantage of delivering 100 times the flux of a silicon monochromator, and thereby makes more efficient use of the continuous synchrotron radiation spectrum, yet preserves the narrow collimation of the incident synchrotron beam. In particular, multilayer x-ray bandwidths, on the order of 1%, are well-matched to x-ray undulator linewidths. Performance results for the X25 multilayer monochromator are presented, comparing it with the silicon monochromator. Of note is its short- and long-term performance as an x-ray monochromator delivering the brightness of the wiggler source in the presence of the high-power white beam. Detailed measurements of its spatial beam profile and wavelength dispersion have been made, and it is shown how its resolution could be improved when desired. Finally, its peculiar, anisotropic resolution function in reciprocal space, and its bearing upon x-ray crystallography and scattering experiments, will be discussed, and highlighted by the results of a protein crystallography experiment. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87844/2/71_1.pd

Cigarette smoking, nicotine dependence and anxiety disorders : a systematic review of population-based, epidemiological studies

Background Multiple studies have demonstrated that rates of smoking and nicotine dependence are increased in individuals with anxiety disorders. However, significant variability exists in the epidemiological literature exploring this relationship, including study design (cross-sectional versus prospective), the population assessed (random sample versus clinical population) and diagnostic instrument utilized.Methods We undertook a systematic review of population-based observational studies that utilized recognized structured clinical diagnostic criteria (Diagnostic and Statistical Manual of Mental Disorders (DSM) or International Classification of Diseases (ICD)) for anxiety disorder diagnosis to investigate the relationship between cigarette smoking, nicotine dependence and anxiety disorders.Results In total, 47 studies met the predefined inclusion criteria, with 12 studies providing prospective information and 5 studies providing quasiprospective information. The available evidence suggests that some baseline anxiety disorders are a risk factor for initiation of smoking and nicotine dependence, although the evidence is heterogeneous and many studies did not control for the effect of comorbid substance use disorders. The identified evidence however appeared to more consistently support cigarette smoking and nicotine dependence as being a risk factor for development of some anxiety disorders (for example, panic disorder, generalized anxiety disorder), although these findings were not replicated in all studies. A number of inconsistencies in the literature were identified.Conclusions Although many studies have demonstrated increased rates of smoking and nicotine dependence in individuals with anxiety disorders, there is a limited and heterogeneous literature that has prospectively examined this relationship in population studies using validated diagnostic criteria. The most consistent evidence supports smoking and nicotine dependence as increasing the risk of panic disorder and generalized anxiety disorder. The literature assessing anxiety disorders increasing smoking and nicotine dependence is inconsistent. Potential issues with the current literature are discussed and directions for future research are suggested

Two-dimensional multiwire gas proportional detector for X-ray photon correlation spectroscopy of condensed matter

Details of a two-dimensional (2-D) multiwire gas proportional detector for X-ray photon correlation spectroscopy (XPCS) of condensed matter are described. The characteristics of the gas proportional detector at 8 keV, 0.3 pC anode charge, and 3 bar (absolute) of Xe/10%CO2 are as follows: 8.5 x 10(-7) counts/s (100 x 100 mu m(2)) dark count rate, similar to mu s time resolution, similar to 48 and 73 mu m position resolution (FWHM) along and across the anode wire direction, respectively, and similar to 80% quantum efficiency. The effects of incident photon energy, anode charge (i.e., gain), gas drift depth, and gas pressure on position resolution are discussed. Static and dynamic speckle patterns, measured from disordered aerogel and polystyrene/polybutadiene blends by a partially coherent synchrotron X-ray source, demonstrate that a 2-D multiwire gas proportional detector is very suitable for the dynamic study of condensed matter with relaxation times in the order of mu s to 10(3) s and atomic length scale