Monitoring elevation variations in leaf phenology of deciduous broadleaf forests from SPOT/VEGETATION time-series

In mountain forest ecosystems where elevation gradients are prominent, temperature gradient-based phenological variability can be high. However, there are few studies that assess the capability of remote sensing observations to monitor ecosystem phenology along elevation gradients, despite their relevance under climate change. We investigated the potential of medium resolution remotely sensed data to monitor the elevation variations in the seasonal dynamics of a temperate deciduous broadleaf forested ecosystem. Further, we explored the impact of elevation on the onset of spring leafing. This study was based on the analysis of multi-annual time-series of VEGETATION data acquired over the French Pyrenees Mountain Region (FPMR), in conjunction with simultaneous ground-based observations of leaf phenology made for two dominant tree species in the region (oak and beech). The seasonal variations in the perpendicular vegetation index (PVI) were analyzed during a five-year period (2002 to 2006). The five years of data were averaged into a one sole year in order to fill the numerous large spatio-temporal gaps due to cloud and snow presence - frequent in mountains - without altering the temporal resolution. Since a VEGETATION pixel (1 km²) includes several types of land cover, the broadleaf forest-specific seasonal dynamics of PVI was reconstructed pixel-by-pixel using a temporal unmixing method based on a non-parametric statistical approach. The spatial pattern of the seasonal response of PVI was clearly consistent with the relief. Nevertheless the elevational or geographic range of tree species, which differ in their phenology sensitivity to temperature, also has a significant impact on this pattern. The reduction in the growing season length with elevation was clearly observable from the delay in the increase of PVI in spring and from the advance of its decrease in the fall. The elevation variations in leaf flushing timing were estimated from the temporal change in PVI in spring over the study area. They were found to be consistent with those measured in situ (R2 > 0.95). It was deduced that, over FPMR, the mean delay of leaf flushing timing for every 100 m increase in elevation was estimated be approximately 2.3 days. The expected estimation error of satellite-based leaf unfolding date for a given elevation was approximately 2 days. This accuracy can be considered as satisfactory since it would allow us to detect changes in leafing timing of deciduous broadleaf forests with a magnitude equivalent to that due to an elevation variation of 100 m (2.3 days on average), or in other words, to that caused by a variation in the mean annual air temperature of 0.5 °C. Although averaging the VEGETATION data over five years led to a loss of interannual information, it was found to be a robust approach to characterise the elevation variations in spring leafing and its long-term trends.     

Collective investigations on two typical semi-insulating GaAs ingots

Due to its high potential technological interest, semi-insulating GaAs has been a material extensively studied for some years. Nevertheless the published results and conclusions are scattered ; comparisons between the various data in litterature are often very risky because of the diversified nature of samples and preparations and also of the diversity of experimental set up used. This paper reports a set of coherent experimental measurements performed on two typical ingots. The first one is grown by horizontal Bridgman method with Cr and Ga₂O₃ added in the melt ; the second one is grown (undoped) by liquid encapsulated (B₂O₃) Czochralski method. The numbered samples were analysed following various physical, optical or electrical technics by different laboratories. Results and conclusions reported here show a good consistancy. Chemical and crystalline homogeneity are especially studied ; the role of chromium doping is also discussed. It is hop ed that this work will help the understanding of GaAs.     

Algodystrophy (reflex sympathetic dystrophy syndrome) and causalgia: novel concepts regarding the nosology, pathophysiology, and pathogenesis of complex regional pain syndromes. Is the sympathetic hyperactivity hypothesis wrong?

Concepts regarding the nosology, pathophysiology and pathogenesis of reflex sympathetic dystrophy syndrome are currently in a state of flux. Causalgia and reflex sympathetic dystrophy syndrome are now generally felt to be on the same continuum and as a result interest for defining criteria for the latter condition has waned. The pathogenic role of adrenergic sympathetic activity has been so successfully challenged that the last international consensus conference judged inappropriate any reference to the sympathetic system in the terms used to designate these conditions, thus confirming the position long defended by most French authors. The vasomotor abnormalities may be due to antidromic release of neuromediators by the endings of polymodal C fibers. These fibers do not belong to the sympathetic system but often travel with sympathetic nerves, a characteristic that may explain the efficacy of sympathetic nerve blocks, although other possibilities exist including a placebo effect. Also, efferent sympathetic fibers may undergo activation by nonadrenergic mediators. The mechanisms capable of initiating and perseverating activation of polymodal C afferents are being actively investigated and have been found to exhibit similarities with the mechanisms underlying peripheral and central sensitization of pain-producing afferents. Growth factors, such as nerve growth factor, may play an important role in causalgia. In "reflex sympathetic dystrophy syndrome", microcirculatory stasis may contribute to the initiation or perpetuatation of the disorders. Further work on the nerve supply to the venular network and on the venoarterial reflex is needed.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Electrostrictive effect in polyurethanes

Polyurethane electrostriction was investigated by measuring the tensile electromechanical coupling coefficients of structurally different materials. True values of the strain coefficients M₃₃₁₁, M₃₃₂₂, and M₃₃₃₃ were obtained for four types of polymer: one commercial polyurethane (DOW 2103‐80 AE) and three polyurethanes synthesized at the Naval Surface Warfare Center, including two phase‐separated (PS) materials with molecular weights of 1000 and 2000 and one phase‐mixed (PM) material with a molecular weight of 2000. Measurements were performed at 2 kHz under a bias field of 4 MV/m at room temperature. Measured values of M₃₃₃₃ ranged from ?9.4 × 10^?18 to ?74.6 × 10^?18 m²/V², with the PM material exhibiting the largest coefficient. The electrostatic interaction (Maxwell stress) did not account for more than 15% of the total electromechanical activity in any of the materials. Furthermore, at the macroscopic level, an empirical relationship was established to predict the values of the electrostrictive coefficients from the dielectric constants and the compliance coefficients of the material. Finally, results indicated that, at the microscopic level, the phenomenon of electrostriction in polyurethanes could be best explained by the presence of charges inside the material (space–charge theory). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 399–404, 2003     

Determination of interfacial tensions for latex particles

The possibility of measuring in situ the interfacial tension at the monomer-swollen polymer-water interface of synthetic latices is considered in detail. Experimental measurements of certain liquid or vapor phase properties of the latex can, in principle, yield values of the desired interfacial tension. This technique requires the evaluation and comparison of the Flory–Huggins term and the Morton term of the thermodynamic expression for the chemical potential of the monomer in the latex particle. While each term can be evaluated, it turns out that the relative magnitudes of the two terms are such that unrealistically high precision is required in the experimental measurements for this technique to be useful for obtaining reasonably accurate interfacial tensions. At saturated swelling conditions with highly surface-active emulsifiers (e.g., sodium dodecyl sulfate), the interfacial tension values obtained have a precision of only about ±50%. The reliability of these approximate values degrades rapidly as one moves away from saturation conditions, so as to render in situ experimental techniques inappropriate for gaining accurate knowledge about the surface energy at the latex particle–water interface at any monomer–polymer ratio. © 1994 John Wiley & Sons, Inc.     

Genomic cloning and species-specific properties of the recombinant canine beta3-adrenoceptor

A molecular clone encoding a beta3-adrenoceptor was isolated from a canine genomic library. The cloned receptor exhibited a pharmacological profile similar to that of other species: in particular, high efficiency of the two selective beta3-adrenoceptor agonists, CL 316,243 (disodium(R,R)-5[2[[2-(chlorophenyl)-2hydroxyethyl]-amino]propyl]- 1,3-benzodioxole-2,2-dicarboxylate) and ICI 201651 ((R)4-(2-hydroxy-3-phenoxypropylaminoethoxy)-N-(2-methoxyethyl)phe noxy acetic acid) and a low affinity for the radioligand (-)-[3-(125)I]-iodocyanopindolol. Interestingly, CGP 12177A ((+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one), which is described as a partial agonist for the human receptor, was a full agonist for the canine receptor. After expression and stimulation of the canine beta3-adrenoceptor in stably transfected Chinese hamster ovary cells there was a very low accumulation of cAMP, suggesting weak coupling to Gs-protein and adenylyl cyclase. However, the response was much better in human embryonal kidney cells transfected with the canine beta3-adrenoceptor gene. The cloning of the canine beta3-adrenoceptor and the insights gained from its pharmacological characterization may allow the development of selective compounds for use in the treatment of obese dogs.     

Comparative measurements between a new logging tool and a reference instrument

Measurements were performed on reference samples (D2O-H2O mixtures) and on highly heterogeneous rocks (Vosges sandstone) with a new logging tool designed to give access to a high spatial resolution, below 1.5 cm on the vertical scale, for a toroidal sensitive volume of 20 cm3. The results were compared to measurements obtained on a clinical magnetic resonance imaging (MRI) equipment working at the same frequency (4.3 MHz). T2 differences as high as 30% were observed for the reference samples; the shortest values were obtained with the logging tool. Porosity profiles of the rock samples were also compared to reference profiles obtained with a conventional computed tomography (CT) scanner. Both nuclear magnetic resonance (NMR) measurements underevaluate porosity by 2-4% for short T2 values (< 10 ms).