Dynamics of Nucleation in Solids: A Self-Consistent Phase Field Approach.

We derive a phase field method for computing rigorously the nucleation rate and the incubation time from the sole knowledge of the free energy of the system in the metastable regime. Our theoretical results are assessed against experimental data relative to demixing of an iron-chromium alloy. Our work clarifies the notions of nucleation rate and incubation time extensively used in classical nucleation theory (CNT) processes in solids. Our work thus emerges as an alternative to CNT but of more general applicability, and enables us to model the nucleation process across the whole range of condition encountered in first order phase transitions, an aspect in which CNT fails.

Strangulated lesser sac hernia.

Internal hernias account for less than 1% of acute mechanical bowel obstruction. Because of their rarety, they are often not considered in the clinical or radiologic diagnosis of bowel obstruction; diagnosis is often delayed, and is most often made at the time of surgery. We present images obtained during the management of a strangulated transomental internal hernia; computerized tomography permitted timely preoperative diagnosis and specifically adapted surgical therapy.

New reactor dedicated to in operando studies of model catalysts by means of surface x-ray diffraction and grazing incidence small angle x-ray scattering.

A new experimental setup has been developed to enable in situ studies of catalyst surfaces during chemical reactions by means of surface x-ray diffraction (SXRD) and grazing incidence small angle x-ray scattering. The x-ray reactor chamber was designed for both ultrahigh-vacuum (UHV) and reactive gas environments. A laser beam heating of the sample was implemented; the sample temperature reaches 1100 K in UHV and 600 K in the presence of reactive gases. The reactor equipment allows dynamical observations of the surface with various, perfectly mixed gases at controlled partial pressures. It can run in two modes: as a bath reactor in the pressure range of 1-1000 mbars and as a continuous flow cell for pressure lower than 10(-3) mbar. The reactor is connected to an UHV preparation chamber also equipped with low energy electron diffraction and Auger spectroscopy. This setup is thus perfectly well suited to extend in situ studies to more complex surfaces, such as epitaxial films or supported nanoparticles. It offers the possibility to follow the chemically induced changes of the morphology, the structure, the composition, and growth processes of the model catalyst surface during exposure to reactive gases. As an example the Pd(8)Ni(92)(110) surface structure was followed by SXRD under a few millibars of hydrogen and during butadiene hydrogenation while the reaction was monitored by quadrupole mass spectrometry. This experiment evidenced the great sensitivity of the diffracted intensity to the subtle interaction between the surface atoms and the gas molecules.

No evidence for proliferation in the blood CD4+ T-cell pool during HIV-1 infection and triple combination therapy.

OBJECTIVE: To evaluate the role of cell proliferation in peripheral blood lymphocyte (PBL) dynamics during HIV infection and potent antiretroviral therapy including protease inhibitors. DESIGN: Transverse study of 150 patients at different stages of infection. Longitudinal study of 50 patients on triple combination antiretroviral therapy with 9-month follow-up. METHODS: Ex vivo incubation of fresh PBL with the DNA biosynthetic marker bromodeoxyuridine (BrdU). Flow cytometric analysis of cell phenotypes and BrdU incorporation. Parallel determination of plasma virus load and CD4+ cell counts. RESULTS: Percentages of BrdU+ B and T lymphocytes found in patients with asymptomatic HIV infection were not different from the low values found in HIV-seronegative controls, and were not correlated with the CD4+ cell count. DNA synthesis increased significantly only during acute opportunistic infections occurring in patients with high plasma viral load and fewer than 100 x 10(6) CD4+ cells/l. Triple combination therapy induced a decrease of plasma virus load and a rise of CD4+ cell counts, whereas BrdU incorporation remained low or decreased. CONCLUSION: Proliferation of peripheral blood T cells observed at late stages of HIV infection corresponds to a response to opportunistic infections. Apart from these particular cases, proliferation in this compartment does not appear as a critical parameter of CD4+ cell kinetics during chronic HIV infection and potent therapy.

[Magnetic resonance study of complex anal fistulae. Preliminary results apropos of 28 cases]. / Exploration par résonance magnétique des fistules anales complexes. Résultats préliminaires à propos de vingt-huit cas.

PURPOSE: To evaluate the use of Magnetic Resonance Imaging (MRI) for the treatment of problematical anal fistulas and follow-up of cases treated by long-term seton drainage with two or three-stage fistulotomy. METHOD: prospective study on 24 patients with surgical treatment between July 1993 and March 1995 selected for MRI among 100 anal suppurations according to following criteria: high trans-sphincteric or supra-sphincteric fistula with one or more previous definitive attempts at treatment (15), and/or severe anal or rectal fibrosis (11). Patients with Crohn's disease were not included. For 14 of these patients who had a long-term seton drainage, MRI tried to assess the quality of the surgical drainage and the course of residual abscess. RESULTS: the overall accuracy of MRI for visualization of internal opening, primary and secondary tract was 84% when compared with surgical data. The sensitivity and specificity were 100% for the detection of horse shoe fistulous tracts (8). For the 14 patients followed by MRI, only one false positive was noted and in 5 cases the results of MRI modified the previous staged procedure (prolonged seton drainage or new excision). For the 20 patients treated for more than 6 months, the mean follow-up was 18 months and median was 14 months. Only one recurrence was noted with no loss of follow-up. CONCLUSION: this study confirms the high degree of accuracy of MRI for mapping of high complex fistula in ano. MRI is very helpful for the survey of healing in cases treated with seton drainage and two or three stage fistulotomy to preserve continence.

[Ano-perineal fistula in MRI. Contribution of T2 weighted sequences]. / Etude des fistules anopérinéales en IRM. Apport des séquences pondérées T2.

INTRODUCTION: Anal fistulae are pathological conditions observed in infections of the Hermann and Defosses' glands or related to Crohn's diseases. The success and the lack of complication of surgical treatment depends on how accurately the tracks are assessed. The contribution of MRI in anal fistulas is now well established but the imaging appearance is not well discribed. The purpose of this work was to discribe the different patterns of lesions. MATERIAL AND METHODS: Eighteen patients with anal fistulas were examined with MRI before operation (mean delay: 14 days. range: 1-56). SE T2 sequences, in coronal and axial planes referred to the anal canal were performed. The examinations were reviewed and compared with the results of surgical assessment to correlate imaging and surgical findings. RESULTS: Lesions were hyperintense on T2-weighted sequences but were also iso- or poorly hyper-intense when they did not contain fluids but only inflammatory tissue. When involving the supra-levator space, lesions were nodular. They were well limited if they occurred in the supra-levator space itself. On the contrary, the rectal wall was thickened and hyper-intense when the fistulous tract reached it. Lesions were similar in Crohn's disease, except for anal fissures which were seen as a tubular hypersignal in contact with the anal lumen. On T2 sequences, healed fistulas were not visible. CONCLUSION: The simple SE T2 sequences can discriminate between different patterns of lesions, especially for supra-levator extensions, fissures in Crohn's disease and chronic inflammatory lesions without fluid. The use of more recent machines or fat suppression sequences may improve the detectability of lesions, especially the more chronic ones.

[Interobserver concordance of echographic semiology in liver cirrhosis]. / Concordance inter-observateurs de la sémiologie échographique de la cirrhose.

OBJECTIVES: The aim of this study was to evaluate the interobserver agreement of cirrhosis symptomatology. METHODS: Eight patients with cirrhosis (without ascites) and 23 patients with chronic liver disease without cirrhosis were included. Four observers (2 juniors and 2 seniors, with 1 specialist and 1 general radiologist in each group) independently evaluated video recordings. Agreement of 18 variables was calculated by using kappa index (k), intraclass correlation coefficient (r) and agreement proportion. Observer bias and poorly trained observers were also investigated. RESULTS: Liver: surface: k = 0.68, homogeneity: k = 0.25, span: r = 0.87, caudate lobe: r = 0.4 to 0.57 according to 3 dimensions, right lobe length: k = 0.33. Veins: portal diameter: r = 0.73, splenic diameter: r = 0.75; umbilical vein: presence: k = 0.19, diameter: r = 0.5; left gastric vein: presence: k = 0, diameter: r = 0.18; spleno-renal shunt: k = 0.41. Spleen length: r = 0.93. Presence of cirrhosis: k = 0.53. The mean agreement for the 18 variables was not significantly different between juniors (0.53 +/- 0.32) and seniors (0.40 +/- 0.38) but was significantly better in specialists (0.61 +/- 0.22) than in general radiologists (0.43 +/- 0.40; P < 0.05). CONCLUSIONS: Interobserver agreement of ultrasonography is good to excellent for the main characteristics of the liver, the main splanchnic veins and spleen but poor to fair for collateral vessels and the caudate lobe. Agreement for diagnosis of cirrhosis is good but should be improved by only selecting reliable signs or experienced echographists.

Dynamic adhesion of CD8-positive cells to antibody-coated surfaces: the initial step is independent of microfilaments and intracellular domains of cell-binding molecules.

Cell adhesion is a multistep, metabolically active process usually requiring several minutes or even hours to complete. This results in the formation of strong bonds that cannot be ruptured by mechanical forces encountered by living cells in their natural environment. However, the first seconds after contact formation are much more sensitive to external conditions and may be the critical step of adhesion. This step is very difficult to monitor without disturbing the observed system. We addressed this problem by studying the interaction between anti-CD8-coated or control surfaces and murine lymphoid cell lines bearing wild-type CD8 molecules, or genetically engineered molecules bearing extracellular CD8 domains and transmembranar and intracytoplasmic domains of class I histocompatibility molecules, or with extensive deletion of intracytoplasmic domains. We used a new method that consisted of monitoring the motion of cells driven along adhesive surfaces by a hydrodynamic force weaker than the reported strength of single ligand-receptor bonds, but sufficient to make free cells move with an easily detectable velocity of several micrometers per second. Cells exhibited short-term (< or = 0.5 s) adhesions to the surface with a frequency of about one event per 30-s period of contact. These events did not require specific antigen-antibody bonds. However, when anti-CD8 were present, strong adhesion was achieved within < 1 s, since most arrests were longer than a standard observation period of 1 min. This bond strengthening was not affected by cytochalasin, and it did not require intact intracellular domains on binding molecules. It is concluded that the initial step in strong adhesion may be viewed as a passive, diffusion-driven formation of a new specific bonds.

Granulocyte-endothelium initial adhesion. Analysis of transient binding events mediated by E-selectin in a laminar shear flow.

The adhesion of moving cells to receptor-bearing surfaces is a key step to many important biological processes. Attachment was subjected to extensive modeling. However, the numerical values of kinetic bonding parameters relevant to realistic models of cell adhesion remain poorly known. In this report, we describe the motion of human granulocytes to interleukin-1-activated endothelial cells in presence of a low hydrodynamic drag (a few piconewtons) estimated to be much weaker than a standard ligand-receptor bond. It was thus expected to visualize the formation and rupture of individual bonds. We observed multiple short-time cell arrests with a median duration of 2.43 s. Stop frequency, not duration, was significantly inhibited by anti-E-selectin antibodies. Binding efficiency exhibited an almost linear relationship with the inverse of cell velocity. The distribution of arrest duration was determined: results were consistent with the view that these arrests reflected the formation/dissociation of single ligand-receptor bonds with a spontaneous dissociation rate of 0.5 s-1. The rate of bond formation was on the order of 0.04 s-1 when cells were freely rolling (mean velocity: 19 microns/s) and it exhibited an approximately 10-fold increase after the formation of a first adhesion.

Motion of cells sedimenting on a solid surface in a laminar shear flow.

Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step.