Transparent solids may show strong absorption when irradiated by a high-intensity laser pulse. Such laser induced breakdown is due to the formation of a free-electron gas. We investigate theoretically the role of ionization processes in a defect-free crystal, including in our model two competing processes: strong-electricfield ionization and electron impact ionization. Free-electron heating is described in terms of electron-phononphoton collisions. Relaxation of the free electron gas occurs through electron-electron collisions and electronphonon collisions. The latter are also responsible for energy transfer from the free-electron gas to the phonon gas. We solve numerically a system of time dependent Boltzmann equations, where each considered process is included by its corresponding collision integral. Our results show formation, excitation, and relaxation of the electron gas in the conduction band. We find that strong-electric-field ionization is mainly responsible for free-electron generation. No avalanche occurs at femtosecond laser irradiation. The electron density and the internal energies of the subsystems are calculated. Critical fluences obtained using various criteria for damage threshold are in good agreement with recent experiments.
In plants, isoprene plays a dual role: (a) as thermo-protective agent proposed to prevent degradation of enzymes/membrane structures involved in photosynthesis, and (b) as reactive molecule reducing abiotic oxidative stress. The present work addresses the question whether suppression of isoprene emission interferes with genome wide transcription rates and metabolite fluxes in grey poplar (Populusxcanescens) throughout the growing season. Gene expression and metabolite profiles of isoprene emitting wild type plants and RNAi-mediated non-isoprene emitting poplars were compared by using poplar Affymetrix microarrays and non-targeted FT-ICR-MS (Fourier transform ion cyclotron resonance mass spectrometry). We observed a transcriptional down-regulation of genes encoding enzymes of phenylpropanoid regulatory and biosynthetic pathways, as well as distinct metabolic down-regulation of condensed tannins and anthocyanins, in non-isoprene emitting genotypes during July, when high temperature and light intensities possibly caused transient drought stress, as indicated by stomatal closure. Under these conditions leaves of non-isoprene emitting plants accumulated hydrogen peroxide (H2O2), a signaling molecule in stress response and negative regulator of anthocyanin biosynthesis. The absence of isoprene emission under high temperature and light stress resulted transiently in a new chemo(pheno)type with suppressed production of phenolic compounds. This may compromise inducible defenses and may render non-isoprene emitting poplars more susceptible to environmental stress.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-010-9654-z) contains supplementary material, which is available to authorized users.
organic linkers with a periodic, nanoscaled structure and ultrahigh surface areas. With their tunable pore/cage sizes, flexible skeleton, and large surface-to-volume ratio, [13][14][15][16][17][18][19] MOFs have a large potential for a wide range of applications, including gas storage and separation, rechargeable batteries, supercapacitors, solar cells, nanoreactors, heterogeneous catalysis, or drug delivery. [20][21][22][23][24][25][26][27] Recently, significant efforts have been devoted to the design and synthesis of new MOFs structures and the investigation of their physical or chemical properties. MOFs are generally prepared as bulk form through traditional hydrothermal or solvothermal synthesis. [28][29][30][31] In order to expand the application range, suitable pathways for the structuring of MOF powders into a functional architecture or devices are highly desirable.Currently, intensive efforts are focusing on the structuring of MOFs at the mesoscopic/macroscopic scale for the use as coatings, membranes, or sophisticated architectures in specific devices and applications. [32][33][34][35] A major difference in the structuring of MOFs into complex shapes compared to inorganic microporous materials, such as zeolites or silica, is the fact that most inorganic binders cannot be used for MOFs as these binders usually require heat treatment. The intrinsic fragility of MOFs needs to be considered which is related to the inorganic/organic hybrid character of this class of materials and the resulting limited thermal and mechanical stability. Alternatively, a more effective way to structure MOFs is the combination with polymer materials. The polymer which acts as a binder improves the mechanical flexibility and ensures chemical stability. Numerous methods have been developed for structuring MOF-polymer compositions including hard or soft templates, spin-or dip-coating, spray-drying, printing, or lithography approaches. [36][37][38] The integration of MOFs into a polymer matrix can result in poor MOF-polymer dispersion and compatibility issues owing to the different physical and chemical properties for the two kinds of materials and this is a challenge in some applications, e.g., in MOF-based mixed matrix membranes for gas separation. [39][40][41][42] The poor interfacial compatibility would lead to agglomeration of MOF particles, causing the formation of nonselective voids between the MOFs particles and the polymer.Electrospinning is a fabrication method to produce continuous ultrafine fibers with diameters in the range of a few tens of nanometers to a few micrometers in the form of nonwoven mats, yarns, etc. The mechanism of electrospinning is based Herein, recent developments of metal-organic frameworks (MOFs) structured into nanofibers by electrospinning are summarized, including the fabrication, post-treatment via pyrolysis, properties, and use of the resulting MOF nanofiber architectures. The fabrication and post-treatment of the MOF nanofiber architectures are described systematically by two routes: i) the dire...
Enzyme immobilization is an established method for the enhancement of enzyme stability and reusability, two factors that are of great importance for industrial biocatalytic applications. Immobilization can be achieved by different methods and on a variety of carrier materials, both organic and inorganic. Inorganic materials provide the advantage of high stability and long service life which, together with the prolonged service life of the immobilized enzyme, can benefit the process economy. However, enzyme immobilization and increased stability often come at the cost of decreased enzyme activity. The main challenges involved in the design of an efficient immobilized enzyme system is to obtain both retention of high enzyme activity, enhanced stability and reusability, which is a complicated task, given the many variables involved, and the large numbers of methods and materials available. Simultaneously, new carrier materials and morphologies are constantly being developed. An investigation of enzyme immobilization systems on inorganic materials, with special emphasis on inorganic membranes, has been conducted in order to evaluate the effects of the immobilization system on the enzyme properties upon immobilization, i.e., activity, stability and reusability. The material properties of the enzyme carriers (particles and membranes) and their effects on the success of immobilization are described here. Furthermore, the reuse of inorganic membranes as enzyme carriers has been investigated and the reported examples show high ability of regeneration. To the best of our knowledge, this is the first review on enzyme immobilization focusing on the three fundamental aspects to consider when dealing with the topic: catalytic properties, enzyme leakage and reusability. Abbreviations: β‐Gal: β‐d‐galactosidase; ADH: alcohol dehydrogenase; AFM: atomic force microscopy; APTES: 3‐aminopropyltriethoxysilane; APTMS: 3‐aminopropyltrimethoxysilane; BPA: bisphenol A; BSA: bovine serum albumin; CA: carbonic anhydrase; CALB: Candida antartica lipase B; CD: circular dichroism; CDI: carbonyldiimidazole; CLEA: cross‐linked enzyme aggregates; CLSM: confocal laser scanning microscopy; CNT: carbon nanotube; CPG: controlled pore glass; CRL: Candida rugosa lipase; DMeDMOS: dimethyldimethoxysilane; DRIFT: diffuse reflectance Fourier transform infrared; E2: 17β‐estradiol; EDC: N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride; EDS: electron dispersive spectroscopy; FDH: formate dehydrogenase; FESEM: field emission scanning microscopy; FT‐IR: Fourier transform infrared spectroscopy; GA: glutaraldehyde; GCSZn: coal fly ashes glass‐ceramic zinc sulfate; GOD: glucose oxidase; GPS: 3‐(glycidyloxypropyl)trimethoxysilane; HDMI: hexamethylene diisocyanate; HRP: horseradish peroxidase; IEP: isoelectric point; IPTES: (3‐isocyanatopropyl)triethoxysilane; IR: infrared spectroscopy; LbL: layer‐by‐layer: MCP: metallic ceramic powder; MeTEOS: methyltriethoxysilane; MF: microfiltration; MML: Mucor miehei lipase; MNP: magnetic nanoparticle; MPTMS: 3‐mercaptopropyltrimethoxysilane; NHS: N‐hydroxysuccinimidyl; PAH: poly(allylamine hydrochloride); PEI: polyethyleneimine; PEG: polyethylene glycol; PES: polyether sulfone; PM‐IRRAS: polarization modulation infrared reflection absorption spectroscopy; pNPA: para‐nitrophenyl acetate; pNPP: para‐nitrophenyl palmitate; PSS: polystyrene sulfonate; PTMS: phenyltrimethoxysilane; ROL: Rhizopus oryzae lipase; SCAD: Saccharomyces cerevisiae alcohol dehydrogenase; SDS: sodium dodecyl sulfate; SDS‐2: sodium dodecyl sulfonate; SEM: scanning electron microscopy; TEM: transmission electron microscopy; TEOS: tetraethoxysilane; TGA: thermogravimetric analysis; TLL: Thermomyces lanuginosa lipase; TMP: transmembrane pressure; TTIP: titanium tetraisoproxide; TVL: Trametes versicolor laccase; UF: ultrafiltration; VTMS: vinyltrimethylsilanemagnified image
A comparison is made of experimental far-wing profiles for the system Li(2P → 3D)He with quantum calculations of thermally averaged free-free continua. Using input adiabatic potentials and transition moment functions from both ab initio and semi-empirical approaches, the comparison shows: (i) new ab initio potentials for Li * (2P, 3P, 3D)He reproduce the spectral positions of the observed rainbow satellites well; the height of the 3D barrier predicted agrees with experiment to within ±15 cm −1 , whereas its position is too large by 0.3 a 0 ; (ii) potentials obtained with various semi-empirical methods reproduce the satellite structure qualitatively, but are generally too repulsive in the 3D state at intermediate and large internuclear separations; (iii) transition moment functions for the asymptotically forbidden 2P → 3P transitions reproduce, with different degrees of accuracy, the intensity of the red-wing satellite related to the 3P potential extremum around 12 a 0 . The vibrational energies in the 2P and 3D states calculated with the ab initio potentials reproduce to within a few cm −1 those obtained from rotationally resolved band spectra reported in the literature.
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