Catalytic reactions with bulk-mediated excursions: mixing fails to restore chemical equilibrium

In this paper we analyze the effect of the bulk-mediated excursions (BME) of reactive species on the long-time behavior of the catalytic Langmuir-Hinshelwood-like A+B-->0 reactions in systems in which a catalytic plane (CP) is in contact with a liquid phase, containing concentrations of reactive particles. Such BME result from repeated particles desorption from the CP, subsequent diffusion in the liquid phase, and eventual readsorption on the CP away from the initial detachment point. This process leads to an effective superdiffusive transport along the CP. We consider both "batch" reactions, in which all particles of reactive species were initially adsorbed onto the CP, and reactions followed by a steady inflow of particles onto the CP. We show that for batch reactions the BME provide an effective mixing channel and here the mean-field-type behavior emerges. On the contrary, for reaction followed by a steady inflow of particles, we observe essential departures from the mean-field behavior and find that the mixing effect of the BME is insufficient to restore chemical equilibrium. We show that a steady state is established as t--> infinity, in which the limiting value of the mean coverage of the CP depends on the particles' diffusion coefficient in the bulk liquid phase, and that the spatial distributions of adsorbed particles are strongly correlated. Moreover, we show that the relaxation to such a steady state is a power-law function of time, in contrast to the exponential time dependence describing the approach to equilibrium in perfectly stirred systems.

Obesity, body fat distribution and incidence of sick leave in the Belgian workforce: the Belstress study

OBJECTIVES

In many studies, obesity has been associated with morbidity or mortality, but only a few have studied the relation between obesity and sick leave. Our aim is to analyse the independent effects of both adiposity and body fat distribution in relation to the 1-y incidence of sick leave in a large cohort of male and female workers covering a variety of occupations, taking into account a wide range of socio-demographic, behavioural and bioclinical variables.

DESIGN AND SETTING

The baseline survey of the Belstress study was conducted in 25 companies across Belgium between 1994 and 1998. A cohort of 20 463 workers (15 557 males and 4906 females) aged 35-59 y was followed for absenteeism during 1 y. The 75th percentile of the distribution of the total annual sickness days was used as a cutoff to classify the workers with a high 1-y incidence rate of sick leave. The relation between sick leave and both obesity and body fat distribution assessed by the body mass index (BMI) and the waist circumference, respectively, was analysed by multivariate logistic regression models.

RESULTS

Using a backward procedure based on the likelihood ratio, we found central abdominal fatness to be an independent predictor of sick leave in both genders (high sick-leave incidence and long spells), but not BMI. In men, the odds ratios was 1.31 (99% CI 1.12-1.52, P<0.0001) and in women it ranged from 1.32 (99% CI 1.03-1.70, P=0.005) to 1.47 (99% CI 1.14-1.90, P<0.0001). Two baseline covariables, respiratory problems and perceived health, are confounders or mediators.

CONCLUSIONS

In this study, body fat distribution was associated with a high annual sick-leave incidence and long spells of sickness absence. If this link is reversible, employers may benefit from programs aiming at the prevention and treatment of central obesity.

Pascal principle for diffusion-controlled trapping reactions

In this paper, we analyze the long-time behavior of the survival probability P(A)(t) of an A particle, that performs lattice random walk in the presence of randomly moving traps B. We show that for both perfect and imperfect trapping reactions, for arbitrary spatial dimension d and for a rather general class of random walks, P(A)(t) is less than or equal to the survival probability of an immobile target A in the presence of randomly moving traps.

Clinical evaluation of a nutraceutical, carprofen and meloxicam for the treatment of dogs with osteoarthritis

The efficacy, tolerance and ease of administration of a nutraceutical, carprofen or meloxicam were evaluated in a prospective, double-blind study on 71 dogs with osteoarthritis. The client-owned dogs were randomly assigned to one of the three treatments or to a placebo control group. The influence of osteoarthritis on the dogs' gait was described by comparing the ground reaction forces of the arthritic dogs and 10 normal dogs. Before the treatments began, and 30 and 60 days later, measurements were made of haematological and biochemical variables and of the ground reaction forces of the arthritic limb, and subjective assessments were made by the owners and by the orthopaedic surgeons. Changes in the ground reaction forces were specific to the arthritic joint, and were significantly improved by carprofen and meloxicam but not by the nutraceutical; the values returned to normal only with meloxicam. The orthopaedic surgeons assessed that there had been an improvement with carprofen and meloxicam, but the owners considered that there had been an improvement only with meloxicam. The blood and faecal analyses did not reveal any changes. The treatments were well tolerated, except for a case of hepatopathy in a dog treated with carprofen.

Corporate ergonomics programme at automobiles Peugeot-Sochaux

An ergonomic assessment tool for design procedures, exclusive to Peugeot-Citroën, called ECM, was developed and applied at the design stage by method technicians in the 1990s. It generates data, which are followed up by the project leader of a new model and ergonomists until two years before each launch. During this time, vehicle design is subject to modification, to adapt to ergonomic demands. Simplified methods (DACORS and METEO) were also developed to assess workstations on the shop floor in trim and final plants. Assessments were used to grade the workstations into four profiles linked to physical and static requirements. Production technicians are responsible for the application of these local methods on the shop floor. The management of these centres aimed to reduce the risks of musculoskeletal disorders by reduced heavy profiles of these stations. New cases of musculoskeletal disorders, surveyed by the company doctor among workers on the assembly lines had decreased since 1996. In 1999, the incidence increased again, despite the pursuit of ergonomic methods. This increase in musculoskeletal disorders was above all linked to a major reorganisation of work conditions, including a reduction in the cycle time on the assembly line, and to a move into a new workshop.

Trapping reactions with randomly moving traps: exact asymptotic results for compact exploration

In a recent paper, Bray and Blythe have shown that the survival probability P(A)(t) of an A particle diffusing with a diffusion coefficient D(A) in a one-dimensional system with diffusive traps B is independent of D(A) in the asymptotic limit t--> infinity and coincides with the survival probability of an immobile target in the presence of diffusive traps. Here, we show that this remarkable behavior has a more general range of validity and holds for systems of an arbitrary dimension d, integer or fractal, provided that the traps are "compactly exploring" the space, i.e., the "fractal" dimension d(w) of traps' trajectories is greater than d. For the marginal case when d(w)=d, as exemplified here by conventional diffusion in two-dimensional systems, the decay form is determined up to a numerical factor in the characteristic decay time.

MRI characteristics of the neurocentral synchondrosis

BACKGROUND AND OBJECTIVES

The neurocentral synchondrosis (NCS) is a cartilaginous growth plate that since the early 1900s has been implicated as a potential cause of adolescent idiopathic scoliosis (AIS). Previous studies have focused only on the closure age without characterizing normal NCS development. Using MRI, the normal development of the NCS image can be characterized, and the stages preceding the disappearance of this image can be specified.

METHODS

A total of 405 NCSs were visualized in 11 normal pediatric patients using T1 and T2 transverse and sagittal MRI views. The images were correlated and the variety of images recorded to categorize the NCS into developmental stages.

RESULTS

The development of the NCS was categorized into five developmental stages. The image of the NCS became absent in a specific pattern along the vertebral column, first in the cervical region (age 6), then in the lumbar region (age 12), and finally in the thoracic region (age 14).

CONCLUSION

The normal development of the NCS at the level of individual vertebrae and also along the vertebral column as a whole was determined using MRI. These patterns of development are valuable and necessary to evaluate the role of the NCS in pathological conditions.

Defect-induced perturbations of atomic monolayers on solid surfaces

We study long-range morphological changes in atomic monolayers on solid substrates induced by different types of defects; e.g., by monoatomic steps in the surface, or by the tip of an atomic force microscope (AFM), placed at some distance above the substrate. Representing the monolayer in terms of a suitably extended Frenkel-Kontorova-type model, we calculate the defect-induced density profiles for several possible geometries. In case of an AFM tip, we also determine the extra force exerted on the tip due to the tip-induced dehomogenization of the monolayer.

Imported viral haemorrhagic fever with a potential for person-to-person transmission: review and recommendations for initial management of a suspected case in Belgium

Viral haemorrhagic fevers are caused by a wide range of viruses. There are 4 types of viruses well known to spread from person to person and able to cause nosocomial outbreaks with a high case fatality rate: an arenavirus (Lassa fever and more exceptionally the Junin and Machupo virus), a bunyavirus (Crimean-Congo haemorrhagic fever) and the Filoviridae (Ebola and Marburg viruses). So far there have been only a limited number of imported cases of viral haemorrhagic fever in industrialized countries. In recent years an increasing number of outbreaks of filovirus infections have occurred in Africa and in 2000 5 cases of Lassa fever were brought from Sierra Leone to Europe. Therefore European physicians should consider the possibility of a viral haemorrhagic fever in an acutely ill patient just returning from Africa or South-America with fever for which there is no obvious cause. Such patients should be questioned for risk factors for viral haemorrhagic fever. Using universal precautions for handling blood and body fluids and barrier nursing techniques there is little risk that if a patient with viral haemorrhagic fever arrives in Belgium there will be secondary cases.

Biodistribution of dual radiolabeled lipidic nanocapsules in the rat using scintigraphy and gamma counting

The aim of the present work was to study the biodistribution of a radiolabeled lipidic nanocapsule formulation after intravenous administration in rat by scintigraphy and gamma counting. This formulation is expected to be used as anticancer agent delivery devices and as transfection complexes. For this purpose, 99mTc-oxine was incorporated in the lipidic core, while 125I labeled tensioactive shell of the nanocapsule. First, in vitro stability of radiolabeled nanocapsules was evaluated by dialysis against distilled water and size measurements. Second, the nanocapsule biodistribution was followed after intravenous administration for 3 h by dynamic scintigraphic acquisition and up to 24 h by determining the gamma activity in blood and tissues. Radiolabeling was efficient and stable in vitro. After intravenous injection blood radioactivity decreased with an early half disappearance time of about 45 min for both radioisotopes. Liver and intestine radioactivities raised up to 24 h. The relatively long remanence in blood of the tracers which is probably due to the presence of PEG at the nanocarrier surface seems promising for the use of these solvent free lipidic nanocapsules as carrier of lipophilic drugs.

In vitro investigation of calcium distribution and tissue thickness in the human thoracic aorta

Atherosclerosis represents a significant cause of morbidity and mortality in the western world. Manifestations of atherosclerotic disease among the elderly include the development of raised lesions that often include calcified regions with material properties similar to bone. There is little information available about the amount and distribution of these calcified plaques within the human aorta, partly due to the difficulty in obtaining this information during in vivo studies. We report the results of a cadaveric investigation of thoracic aortic wall thickness, diameter and calcium content. A non-destructive x-ray imaging technique was used to obtain two-dimensional maps of total thickness and mineral content in excised thoracic aortic specimens. In a study of 39 individuals (23 male and 16 female, aged 20-92 years) we report a significant non-linear correlation between calcium burden and age, with calcium deposition most commonly occurring proximal to the ostia of major branching vessels. We also found a significant linear correlation between age and both total aortic wall thickness and aortic diameter. An improved understanding of the pathological changes in the ageing thoracic aorta may be useful in the development of strategies to reduce the undesirable vessel calcification associated with atherosclerosis.

[Calcium and bioluminescent probes]

Ca2+ is an universal second messenger in numerous cell physiological processes. Aequorin, a bioluminescent calcium-binding protein is used today as a cellular probe to measure and image variations in calcium concentrations. The paper describes the characteristics and the use of aequorin as a luminescent calcium probe, and the future in the use of this protein for calcium imaging.

[HIV-1 Tat protein induces IL-10 production by human monocytes: implications of the PKC and calcium pathway]

In asymptomatic patients infected by HIV-1, the level of IL-10, a cytokine with immunosuppressive activity, is associated with the course of HIV infection towards AIDS. We show that HIV-1 Tat, a viral protein secreted by infected cells, induces IL-10 production by human peripheral blood monocytes. The analysis of the signal transduction pathways strongly suggests that the protein kinase C may play an essential role in this induction. Stimulation by Tat induces nuclear translocation of the transcription factor NFkB the activation of which seems to be necessary for IL-10 production. Using microspectrofluorimetry and confocal microscopy, we also show that Tat induces a calcium influx.

[Calcium-dependent pathways involved in the production of cytokines in lymphocytes]

CD4+ T lymphocytes are divided in Th1 cells producing IFN gamma and Th2 cells that synthetize IL-4. This paper describes signaling pathways activated following T cell receptor (TCR) engagement and emphasizes differences that can account for differential cytokine production. This paper focuses on a new signaling pathway involved in IL-4 synthesis. This pathway couples the TCR to PKC that controls a calcium entry through dihydropyridine sensitive calcium channels. The calcium response is sufficient to initiate IL-4 gene transcription. Differing from that of IL-4, IFN gamma gene expression always requires MAP-kinase activation in addition to a calcium signal.

[Neural determination in Xenopus laevis embryos: control of early neural gene expression by calcium]

In amphibian embryos the central nervous system derives from the dorsal region of the ectoderm. Molecular studies led to the formulation of the "neural default model" in which neural development is under the inhibitory control of members of the BMP family. These growth factors also act as epidermis inducers. The neural fate is revealed by factors secreted by the Spemann Organizer such as noggin, chordin, follistatin, Xnr3 and cerberus which act by blocking BMP signalling. We propose a new model for neural cell determination in which a signalling pathway controlled by an increase in intracellular calcium suppresses the epidermis fate and activates the neural fate instead. This increase in calcium is due to an influx through calcium channels of the L-type, expressed in ectodermal cells during gastrulation. The possible involvement of a calcium-dependent phosphatase (calcineurin) to inhibit the epidermis fate and a calcium-calmodulin kinase (CaMkinase II) which activates the neural fate is discussed.

The components of the magnetic resonance image of the neurocentral junction

The neurocentral junction (NCJ) is a cartilaginous growth plate located between the vertebral centrurn and the neural arch. In characterizing the age of closure of this growth plate, anatomic studies have suggested that the NCJ closes before age 10, whereas MRI studies have suggested that the NCJ does not fuse until adolescence In this study, gross anatomic and histologic sections were correlated with MR images to determine the components of the NCJ image. The NCJ image appeared as a thick white line that was shown to encompass the cartilage of the growth plate, the surrounding woven bone and a portion of the trabecular bone of the vertebra. Although the MR pixels were too large to completely resolve the tissues that surround the growth plate, MRI was shown to be a valuable technique of visualizing the NCJ cartilage and further MRI studies of the human NCJ are needed.

Assessing the impact of pelvic obliquity in post-operative neuromuscular scoliosis

The goal of this pilot study was to explore the relationship between pelvic obliquity and patient pain, sitting tolerance, pressure sores, and function. Five neuromuscular patients who underwent spinal surgery 6-26 weeks prior to assessment took part in this on-going study (4F; 1M); age at surgery (14.6 +/- 2.6 years). Pelvic obliquity was measured from pre- and post-operative anterior-posterior radiographs. A force-sensing pad with a grid of sensors was placed on a flat surface and the weight distribution pattern was recorded. The pressures were divided into left and right sides and peak levels were noted on each side. The parents or caregivers completed a questionnaire on their child's pain, sitting tolerance, pressure sores, and functional abilities. Pelvic obliquity was reduced after surgery by approximately 50% depending on the method used to assess pelvic obliquity. The major curve was reduced from 64 degrees(10 degrees) to 39 degrees (10 degrees). Post operatively, the average pressure (left/right side) ranged from 1.2 to 2.0 (average 1.6). The peak pressure ratio ranged from 1.1 to 1.9 (average 1.4). The ratio of left/right pressure correlated with improvement in pelvic obliquity (r2=0.9). Pain was moderate/severe in the 2 patients with the least correction as measured with the Cobb angle from surgery; both improved following surgery. Two patients suffered pressure sores pre-operatively and one post-operatively. Only 3/5 felt sitting endurance had increased. All parents felt their child sat straighter after surgery. The outcome measures of pain, pressure sores, sitting tolerance, and function were not well related to the amount of pelvic obliquity. More candidates and a longer follow-up may shed light on the many relationships.