Extensibility and rheology of collenchyma I. Creep relaxation and viscoelasticity of young and senescent cells

The extensibility of collenchyma cells was methodologically analyzed; extensibility (elasticity and plasticity) and rheology of this tissue are discussed. Experimental conditions are described. Rheological data for young and senescent cells were obtained; they were found to be not Boltzmannian. The permanent strain is not viscous, and is larger for young cells than older one

Extensibility and rheology of collenchyma cells: II. Low-pH effect on the extension of collocytes isolated from high- and low-growing material

Low-pH effects were studied on the extension of isolated fresh, methanol-killed and frozen-thawed collocytes. Fresh and frozen-thawed samples responded to low pH. This response decreased with increasing differentiation. A yield stress was found for frozen-thawed samples. The significance of the response during growth and differentiation is discusse

Non-luminescent disexcitation of F-center pairs by exchange-softened vibrational modes

The non-luminescent and spin-dependent disexcitation process observed in F-center pairs in alkali halides at low temperature is explained by a covalent bond within the pair. Exchange effects give a negative contribution to the lattice potential energy. If the pair separataion is small, local modes become unstable and spontaneous lattice distortions bring back the pair in its ground state

EPR optical detection of F centre pairs in alkali halides. - I : Pumping cycle kinetics and characteristics of the resonances

The EPR of F centres in the ground and excited states was optically detected in the following alkali halide crystals: NaCl, KF, KCl, KBr, KI, RbBr, and RbI. A decrease of the radiative quantum efficiency of the F centre luminescence was observed when microwave transitions were induced between the spin levels. The mechanism responsible for this effect was an electronic tunnelling through the crystal field potential; the electron in the relaxed excited state of an F centre (F~*) is transferred nonradiatively to another nearby F centre in its ground state (F0), and leads to the momentary formation of an ƒ¿ and an F\u27 centre. Such a process is a function of the total spin of the F~*-F0 pair. The role played by the paired centres was confirmed by measurements at different F centre concentration. Moreover, at high optical excitation pumping rates, the population of the intermediate complexes (F\u27-ƒ¿) is large enough to allow an estimation of the rate of the reverse process F\u27 + ƒ¿ \u27¨ F0 + F0

Optical and ESR studies on an IR absorption band in CsI:Na after x-ray irradiation

The nature of the defect giving rise to a near IR absorption band (717 nm)in x-irradiated CaI:Na by measuring its linear dichroism, its magnetic CD and its change due to the resonance microwave was studied. The defect (g|| = 1.96, g\u27Û = 2.23 with axis near 100\u27r) involves a Na+ ion and an excess electron

A 1-Year Prospective French Nationwide Study of Emergency Hospital Admissions in Children and Adults with Primary Immunodeficiency.

PURPOSE: Patients with primary immunodeficiency (PID) are at risk of serious complications. However, data on the incidence and causes of emergency hospital admissions are scarce. The primary objective of the present study was to describe emergency hospital admissions among patients with PID, with a view to identifying "at-risk" patient profiles. METHODS: We performed a prospective observational 12-month multicenter study in France via the CEREDIH network of regional PID reference centers from November 2010 to October 2011. All patients with PIDs requiring emergency hospital admission were included. RESULTS: A total of 200 admissions concerned 137 patients (73 adults and 64 children, 53% of whom had antibody deficiencies). Thirty admissions were reported for 16 hematopoietic stem cell transplantation recipients. When considering the 170 admissions of non-transplant patients, 149 (85%) were related to acute infections (respiratory tract infections and gastrointestinal tract infections in 72 (36%) and 34 (17%) of cases, respectively). Seventy-seven percent of the admissions occurred during winter or spring (December to May). The in-hospital mortality rate was 8.8% (12 patients); death was related to a severe infection in 11 cases (8%) and Epstein-Barr virus-induced lymphoma in 1 case. Patients with a central venous catheter (n = 19, 13.9%) were significantly more hospitalized for an infection (94.7%) than for a non-infectious reason (5.3%) (p = 0.04). CONCLUSION: Our data showed that the annual incidence of emergency hospital admission among patients with PID is 3.4%. The leading cause of emergency hospital admission was an acute infection, and having a central venous catheter was associated with a significantly greater risk of admission for an infectious episode

Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO₂ rise

A rise in the atmospheric CO2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO2, and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO2 in the ocean interior, possibly explaining the Holocene atmospheric CO2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene