Neutron diffraction studies on liquids

The above examples serve to illustrate the extent to which neutron diffraction isotopic substitution methods have been used to determine interatomic structure in a wide range of liquid and amorphous systems. The direct determination of pair radial functions not only offers a means of characterising the different structures in liquids, but also provides theorists with information to construct more realistic model potentials which can be used to explore properties in regimes not currently accessible to experiment.\ud \ud It is anticipated that the NDIS methods will continue to be developed and applied to a wider range of systems. The construction and commissioning of new diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions will enable new and more extensive research to be undertaken. Besides the many problems of immediate interest suggested at the end of some sections, there are several investigations which will become feasible in the longer term as the technology develops. These include: (i) the use of isotopes such as 12C and 13C which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and (ii) the exploitation of higher count rates to investigate changes of structure as a chemical reaction occurs

Neutron and X-ray diffraction studies on complex liquids

The above examples illustrate the extent to which present day neutron and X-ray diffraction methods are being used to determine interatomic structure in a wide range of liquid and amorphous systems. The determination of pair radial distribution functions not only offers a means to characterise different structures in liquids, but also provides theorists with information to construct realistic model potentials that can be used to calculate macroscopic behaviour and structural properties in regimes not currently accessible to experiment.\ud The well-established NDIS difference methods remain superior to all other methods for the determination of interatomic pairwise structure. The relatively new AXD (or DAS) difference methods have the potential to answer long-standing questions about the structure around species with mass number greater than about 30. However, the relatively low X-ray scattering power from light elements such as hydrogen, carbon, nitrogen etc. means that it will never be possible to resolve completely structures of biologically important liquids by X-ray methods alone. EXAFS spectroscopy has the distinct advantage over both diffraction techniques as it can be used to study local structure around particular species at high dilution. Therefore studies which combine reference data from AXD or NDIS, with extensive EXAFS data, are likely to be useful in studies of structure in regimes which prove difficult for AXD and NDIS. \ud It is clear that no one method will be sufficient to resolve structure at the required level of detail around all species in a complex liquid. Instead one must rely on a full complement of diffraction and other techniques including computer simulation to determine the complete atomic structure of a complex liquid or amorphous system.\ud On the technical front, the construction and commissioning of new neutron diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions, will enable new and more extensive research to be undertaken. Additionally, the new custom-built X-ray diffractometer for liquids proposed for the DIAMOND synchrotron being established at RAL will provide a much-needed boost for wide-ranging AXD and EXAFS investigations of complex liquids. \ud Besides the many studies of immediate interest suggested at the end of some sections, there are several investigations that will become feasible in the longer term as the technology develops. These include 1. the use of isotopes such as 12C and 13C and 33S and 32S which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and 2. the exploitation of higher neutron and X-ray count rates to facilitate real time experiments to investigate changes of structure as a chemical or biochemical reaction occurs. \ud The one strong theme which emerges from all the work described in this paper is that diffraction, especially that based on difference techniques, remains the best means to determine structure at atomic resolution in complex liquids

On the evolutionary and pulsation mass of Classical Cepheids: III. the case of the eclipsing binary Cepheid CEP0227 in the Large Magellanic Cloud

We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass, age) of the eclipsing binary system CEP0227 in the LMC. We computed evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were constructed either by neglecting or by including a moderate convective core overshooting (beta=0.2) during central H-burning phases. Models were also constructed either by neglecting or by assuming a canonical (eta=0.4,0.8) or an enhanced (eta=4) mass loss rate. The solutions were computed in three different planes: luminosity-temperature, mass-radius and gravity-temperature. By using the Bayes Factor, we found that the most probable solutions were obtained in the gravity-temperature plane with a Gaussian mass prior distribution. The evolutionary models constructed by assuming a moderate convective core overshooting (beta=0.2) and a canonical mass loss rate (eta=0.4) give stellar masses for the primary Cepheid M=4.14^{+0.04}_{-0.05} M_sun and for the secondary M=4.15^{+0.04}_{-0.05} M_sun that agree at the 1% level with dynamical measurements. Moreover, we found ages for the two components and for the combined system t=151^{+4}_{-3} Myr that agree at the 5% level. The solutions based on evolutionary models that neglect the mass loss attain similar parameters, while those ones based on models that either account for an enhanced mass loss or neglect convective core overshooting have lower Bayes Factors and larger confidence intervals. The dependence on the mass loss rate might be the consequence of the crude approximation we use to mimic this phenomenon. By using the isochrone of the most probable solution and a Gaussian prior on the LMC distance, we found a distance modulus 18.53^{+0.02}_{-0.02} mag and a reddening value E(B-V)= 0.142^{+0.005}_{-0.010} mag that agree well with literature estimates.Comment: Accepted for publication in ApJ. 17 pages, 9 figure

Immunolocalization of fibroblast growth factor-1 (FGF-1), its receptor (FGFR-1), and fibroblast-specific protein-1 (FSP-1) in inflammatory renal disease

Immunolocalization of fibroblast growth factor-1 (FGF-1), its receptor (FGFR-1), and fibroblast-specific protein-1 (FSP-1) in inflammatory renal disease.BackgroundThe fibroblast growth factor (FGF) family has functions in development, cell proliferation, migration, and differentiation. While FGF-2 induces fibrosis, the role of FGF-1 in inflammation and fibrosis is less defined. We examined the expression of FGF-1 and FGF receptor (FGFR-1) to determine if renal diseases with varying etiologies of inflammation, including lupus nephritis (LN), acute interstitial nephritis (AIN) and acute rejection superimposed on chronic allograft nephropathy (CAN), showed varying patterns of expression. We also examined the expression of fibroblast-specific protein-1 (FSP-1), which has been linked to epithelial-mesenchymal transition (EMT) and fibrosis, to determine whether it was linked to potential profibrotic and inflammatory FGF-1 mechanisms.MethodsProliferative LN (PLN) (N = 12), nonproliferative lupus nephritis (NPLN) (N = 5), AIN (N = 6), CAN (N = 4), and normal kidneys (N = 3) were studied. FGF, FGFR-1, and FSP-1 were localized by immunohistochemistry, and intensity scored on a 0 to 3+ scale. Double staining with CD68 and separate immunohistochemical staining for CD4 and CD8 with serial sections analysis were done to identify if T lymphocytes or macrophages showed staining for FGF-1 and FGFR-1 or FSP-1.ResultsIn normal kidneys, FGF-1 was expressed in mesangial cells (0.67 ± 0.58), glomerular endothelial (0.67 ± 0.58), visceral, and parietal epithelial cells (1.67 ± 0.58). FGFR-1 showed a similar pattern of staining but also was expressed in tubular epithelium, and arterial endothelium and smooth muscle. Expression of FGF-1 was increased over normal in glomerular parenchymal cells only in CAN in podocytes (2.30 ± 0.58 vs. 3.00 ± 0.00) (P < 0.05) and parietal epithelial cells (1.67 ± 0.58 vs. 2.25 ± 0.50) (P < 0.05). Infiltrating glomerular and interstitial inflammatory cells in diseased glomeruli also expressed FGF-1 and FGFR-1. Tubular cells expressed slightly increased FGFR-1 in renal diseases vs. normal, whereas tubules remained negative for FGF-1 in diseased kidneys. FSP-1 expression was prominent in the interstitium in all kidneys with interstitial inflammation, and most prominent in CAN. Interstitial FSP-1+ cells were consistent with a myofibroblast-type morphology, and did not stain with CD-68. FSP-1 expression was closely associated with inflammatory cells expressing FGF-1 and FGFR-1. FSP-1 also showed positivity within crescents and occasional podocytes in PLN.ConclusionThe expression of FGF-1 and FGFR-1 in infiltrating lymphocytes and macrophages, and of FGFR-1 in tubules, is supportive, but does not prove causality, of the possibility that FGF-1 might have both autocrine and paracrine functions in renal inflammation. However, the initial stimulus for renal inflammation, whether immune complex, hypersensitivity or rejection, did not alter expression patterns of FGF-1 or its receptor. The colocalization of inflammatory infiltrates with interstitial fibrosis supports the possibility of a contribution of FGF-1 for chemotaxis and associated fibrosis, further supported by interstitial FSP-1 expression closely associated with these inflammatory cells expressing FGF-1 and FGFR-1

Many-body correlations probed by plasmon-enhanced drag measurements in double quantum well structures

Electron drag measurements of electron-electron scattering rates performed close to the Fermi temperature are reported. While evidence of an enhancement due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys. Rev. Lett. 73, 3572 (1994)], is found, important differences with the random-phase approximation based calculations are observed. Although static correlation effects likely account for part of this difference, it is argued that correlation-induced multiparticle excitations must be included to account for the magnitude of the rates and observed density dependences.Comment: 4 pages, 3 figures, revtex Accepted in Phys. Rev.

Dynamic correlations in symmetric electron-electron and electron-hole bilayers

The ground-state behavior of the symmetric electron-electron and electron-hole bilayers is studied by including dynamic correlation effects within the quantum version of Singwi, Tosi, Land, and Sjolander (qSTLS) theory. The static pair-correlation functions, the local-field correction factors, and the ground-state energy are calculated over a wide range of carrier density and layer spacing. The possibility of a phase transition into a density-modulated ground state is also investigated. Results for both the electron-electron and electron-hole bilayers are compared with those of recent diffusion Monte Carlo (DMC) simulation studies. We find that the qSTLS results differ markedly from those of the conventional STLS approach and compare in the overall more favorably with the DMC predictions. An important result is that the qSTLS theory signals a phase transition from the liquid to the coupled Wigner crystal ground state, in both the electron-electron and electron-hole bilayers, below a critical density and in the close proximity of layers (d <~ r_sa_0^*), in qualitative agreement with the findings of the DMC simulations.Comment: 13 pages, 11 figures, 2 table

Phases in Strongly Coupled Electronic Bilayer Liquids

The strongly correlated liquid state of a bilayer of charged particles has been studied via the HNC calculation of the two-body functions. We report the first time emergence of a series of structural phases, identified through the behavior of the two-body functions.Comment: 5 pages, RevTEX 3.0, 4 ps figures; Submitted to Phys. Rev. Let

Dynamic exchange-correlation potentials for the electron gas in dimensionality D=3 and D=2

Recent progress in the formulation of a fully dynamical local approximation to time-dependent Density Functional Theory appeals to the longitudinal and transverse components of the exchange and correlation kernel in the linear current-density response of the homogeneous fluid at long wavelength. Both components are evaluated for the electron gas in dimensionality D=3 and D=2 by an approximate decoupling in the equation of motion for the current density, which accounts for processes of excitation of two electron-hole pairs. Each pair is treated in the random phase approximation, but the role of exchange and correlation is also examined; in addition, final-state exchange processes are included phenomenologically so as to satisfy the exactly known high-frequency behaviours of the kernel. The transverse and longitudinal spectra involve the same decay channels and are similar in shape. A two-plasmon threshold in the spectrum for two-pair excitations in D=3 leads to a sharp minimum in the real part of the exchange and correlation kernel at twice the plasma frequency. In D=2 the same mechanism leads to a broad spectral peak and to a broad minimum in the real part of the kernel, as a consequence of the dispersion law of the plasmon vanishing at long wavelength. The numerical results have been fitted to simple analytic functions.Comment: 13 pages, 11 figures included. Accepted for publication in Phys. Rev.