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121.
122.
Amitava Datta 《Pramana》1993,40(6):L503-L509
It is argued with the help of an illustrative model, that the inter species hierarchy among the fermion masses and the quark
mixing angles can be accommodated naturally in the standard model with (approximate) flavor democracy provided there are three
exactly massless neutrinos and four families of sequential quark-leptons with all members of the fourth family having roughly
equal masses. The special problem of light neutrino masses (if any) and possible solutions are also discussed. 相似文献
123.
A temperature-dependent integrated kinetics for the overall process of photosynthesis in green plants is discussed. The C4 plants are chosen and in these plants, the rate of photosynthesis does not depend on the partial pressure of O2. Using some basic concepts like chemical equilibrium or steady state approximation, a simplified scheme is developed for
both light and dark reactions. The light reaction rate per reaction center (R′
1) in thylakoid membrane is related to the rate of exciton transfer between chlorophyll neighbours and an expression is formulated
for the light reaction rate R′
1. A relation between R′
1 and the NADPH formation rate is established. The relation takes care of the survival probability of the membrane. The CO2 saturation probability in bundle sheath is also taken into consideration. The photochemical efficiency (ϕ) is expressed in terms of these probabilities. The rate of glucose production is given by R
glucose = (8/3)(R′
1
v
L
)ϕ(T)
g
(T) ([G3P]/[P
i]2
leaf)SS
Q
G3P→glucose where g is the activity quotient of the involved enzymes, and G3P represent glycealdehyde-3-phosphate in steady state. A Gaussian
distribution for temperature-dependence and a sigmoid function for de-activation are incorporated through the quotient g. In general, the probabilities are given by sigmoid curves. The corresponding parameters can be easily determined. The theoretically
determined temperature-dependence of photochemical efficiency and glucose production rate agree well with the experimental
ones, thereby validating the formalism. 相似文献
124.
This paper presents an overview of the recent results on upconversion and photoluminescence of rare-earth ions in nanoenvironments.
The role of the rare-earth ion concentration, crystal size and crystal phase on the up and downconversion emission of rare-earth
ions in oxide nanocrystals and their underlying mechanisms are discussed. It is also found that the luminescence lifetime
of the excited state rare-earth ions is sensitive to the particle crystalline phase and size. The analysis suggests that the
modifications of radiative and nonradiative relaxation mechanisms are due to local symmetry structure of the host lattice
and crystal size respectively 相似文献
125.
Lanthanide‐Doped Nanocrystals: Strategies for Improving the Efficiency of Upconversion Emission and Their Physical Understanding 下载免费PDF全文
The fundamental understanding of lanthanide‐doped upconverted nanocrystals remains a frontier area of research because of potential applications in photonics and biophotonics. Recent studies have revealed that upconversion luminescence dynamics depend on host crystal structure, size of the nanocrystals, dopant concentration, and core–shell structures, which influence site symmetry and the distribution and energy migration of the dopant ions. In this review, we bring to light the influences of doping/co‐doping concentration, crystal phase, crystal size of the host, and core–shell structure on the efficiency of upconversion emission. Furthermore, the lattice strain, due to a change in the crystal phase and by the core–shell structure, strongly influences the upconversion emission intensity. Analysis suggests that the local environment of the ion plays the most significant role in modification of radiative and nonradiative relaxation mechanisms of overall upconversion emission properties. Finally, an outlook on the prospects of this research field is given. 相似文献
126.
Dr. Arik Kar Sumanta Sain Dr. Simanta Kundu Arka Bhattacharyya Dr. Swapan Kumar Pradhan Prof. Amitava Patra 《Chemphyschem》2015,16(5):1017-1025
Tuning the functional properties of nanocrystals is an important issue in nanoscience. Here, we are able to tune the photocatalytic properties of SnO2 nanocrystals by controlling their size and shape. A structural analysis was carried out by using X‐ray diffraction (XRD)/Rietveld and transmission electron microscopy (TEM). The results reveal that the number of oxygen‐related defects varies upon changing the size and shape of the nanocrystals, which eventually influences their photocatalytic properties. Time‐resolved spectroscopic studies of the carrier relaxation dynamics of the SnO2 nanocrystals further confirm that the electron–hole recombination process is controlled by oxygen/defect states, which can be tuned by changing the shape and size of the materials. The degradation of dyes (90 %) in the presence of SnO2 nanoparticles under UV light is comparable to that (88 %) in the presence of standard TiO2 Degussa P‐25 (P25) powders. The photocatalytic activity of the nanoparticles is significantly higher than those of nanorods and nanospheres because the effective charge separation in the SnO2 nanoparticles is controlled by defect states leading to enhanced photocatalytic properties. The size‐ and shape‐dependent photocatalytic properties of SnO2 nanocrystals make these materials interesting candidates for photocatalytic applications. 相似文献
127.
128.
Jiri Kudr Sylvie Skalickova Lukas Nejdl Amitava Moulick Branislav Ruttkay–Nedecky Vojtech Adam Rene Kizek 《Electrophoresis》2015,36(19):2367-2379
Nanofluidics is becoming an extensively developing technique in the field of bioanalytical chemistry. Nanoscale hole embed in an insulating membrane is employed in a vast variety of sensing platforms and applications. Although, biological nanopores have several attractive characteristics, in this paper, we focused on the solid‐state nanopores due to their advantages as high stability, possibility of diameter control, and ease of surface functionalizing. A detection method, based on the translocation of analyzed molecules through nanochannels under applied voltage bias and resistive pulse sensing, is well established. Nevertheless, it seems that the new detection methods like measuring of transverse electron tunneling using nanogap electrodes or optical detection can offer significant additional advantages. The aim of this review is not to cite all related articles, but highlight the steps, which in our opinion, meant important progresses in solid‐state nanopore analysis. 相似文献
129.
Topochemical Transformations of CaX2 (X=C,Si, Ge) to Form Free‐Standing Two‐Dimensional Materials 下载免费PDF全文
Saied Md. Pratik A. Nijamudheen Prof. Dr. Ayan Datta 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18454-18460
Topochemical transformations of layered materials CaX2 (X=Si, Ge) are the method of choice for the high‐yield synthesis of pristine, defect‐free two‐dimensional systems silicane and germanane, which have advanced electronic properties. Based on solid‐state dispersion‐corrected calculations, mechanisms for such transformations are elucidated that provide an in‐depth understanding of phase transition in these layered materials. While formation of such layered materials is highly favorable for silicane and germanane, a barrier of 1.2 eV in the case of graphane precludes its synthesis from CaC2 topochemically. The energy penalty required for distorting linear acetylene into a trans‐bent geometry accounts for this barrier. In contrast it is highly favorable in the heavier analogues, resulting in barrierless topochemical generation of silicane and germanane. Photochemical generation of the trans‐bent structure of acetylene in its first excited state (S1) can directly generate graphane through a barrierless condensation. Unlike the buckled structure of silicene, the phase‐h of CaSi2 with perfectly planar silicene layers exhibits the Dirac cones at the high symmetry points K and H. Interestingly, topochemical acidification of the cubic phase of calcium carbide is predicted to generate the previously elusive platonic hydrocarbon, tetrahedrane. 相似文献
130.