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51.
Twenty three at‐risk high school female students who had failed mathematics and science in a traditional school setting were the subjects of this study that integrated mathematics and science lessons over a period of four weeks. Using a combination of direct instruction, calculations, graphing, hands‐on projects, and discussion, the topic of mechanical advantage was studied, to find out how well students understood the topic. The study found that these students who initially knew very little about mechanical advantage, and who did not see any need to use mathematics in the study of science, indicated an increased understanding of mechanical advantage, and also seemed to realize that integrating mathematics and science enhanced learning. 相似文献
52.
T V Ramakrishnan 《Pramana》2002,58(2):149-153
Some problems in the physics of disordered systems are pointed out; most of these arise from experiments. 相似文献
53.
54.
Parthasarathy R Bykhovski A Gelmont B Globus T Swami N Woolard D 《Physical review letters》2007,98(15):153906
In this work, a theoretical study of the coupling of TM polarized subterahertz (THz) radiation with periodic semiconductor rectangular slot arrays was conducted, using InSb as an example. Simulation results showed that the structure with 4-12 microm thickness provides over a 20-30-fold increase in the electric field at slot edges in a nanosize region ( approximately 500 nm). The enhancement of the THz electromagnetic field extends across the slots and reaches peak values at the edges due to discontinuity effects. Because of the strong local electromagnetic field enhancement, the structure can potentially be used for the development of novel biophotonic sensors, leading to improved detection sensitivity. 相似文献
55.
Ashokkumar P Ramakrishnan VT Ramamurthy P 《The journal of physical chemistry. A》2011,115(50):14292-14299
Ratiometric sensors for the detection of metal ions have gained increasing attention due to its self-calibration tendency for the environmental effects. In this context, we have synthesized and characterized a dual emitting ratiometric Zn(2+) probe (1) having acridinedione as a fluorophore and N,N-bis(2-pyridylmethyl)amine (BPA) as a receptor unit. Existence of two different conformation of the molecule with photoinduced electron transfer (PET) from amine moiety to the acridinedione fluorophore leads to dual emission, namely locally excited (425 nm) and anomalous charge transfer emission (560 nm) in aprotic solvents. In the presence of one equivalent of Zn(2+), a 15-fold fluorescence enhancement in the locally excited state together with the quenching of charge transfer emission is observed. The intensity changes at the two emission peaks allow a ratiometric detection of Zn(2+) under PET signaling mechanism. The utilization of PET process for the ratiometric fluorescence change will further signify the importance of PET mechanism in sensing action. Addition of Zn(2+) to 1 in acetonitrile/water mixtures shows a single emission peak with fluorescence enhancement. 相似文献
56.
Robust Stability Criteria for Uncertain Neutral Systems with Interval Time-Varying Delay 总被引:1,自引:0,他引:1
In this paper, we consider the problem of robust stability of a class of linear uncertain neutral systems with interval time-varying
delay under (i) nonlinear perturbations in state, and (ii) time-varying parametric uncertainties using Lyapunov-Krasovskii
approach. By constructing a candidate Lyapunov-Krasovskii (LK) functional, that takes into account the delay-range information
appropriately, less conservative robust stability criteria are proposed in terms of linear matrix inequalities (LMI) to compute
the maximum allowable bound for the delay-range within which the uncertain neutral system under consideration remains asymptotically
stable. The reduction in conservatism of the proposed stability criterion over recently reported results is attributed to
the fact that time-derivative of the LK functional is bounded tightly without neglecting any useful terms using a minimal
number of slack matrix variables. The analysis, subsequently, yields a stability condition in convex LMI framework, that can
be solved non-conservatively at boundary conditions using standard LMI solvers. The effectiveness of the proposed stability
criterion is demonstrated through standard numerical examples. 相似文献
57.
Koteeswari R Ashokkumar P Malar EJ Ramakrishnan VT Ramamurthy P 《Chemical communications (Cambridge, England)》2011,47(27):7695-7697
Amidothiourea linked acridinedione derivatives selectively detect Hg(2+) in unbuffered aqueous solution under broad pH range with both single- and two-photon excitation. The observed linear fluorescence intensity change allows the quantitative detection of Hg(2+) in the concentration range of 22 nM-0.33 μM with the lower detection limit of 2 nM. 相似文献
58.
Intense Raman scattering by acetophenone molecules adsorbed on colloidal silver particles is reported. Greater enhancement
is observed for the ring breathing and ring stretching vibrations. The orientation determination analysis shows that the adsorption
of acetophenone molecule is neither through its co-ordinating site nor through itsπ-orbital system and there is no strong chemical interaction. However significant intensity enhancement for several vibrations
suggests that the contribution is from classical electromagnetic field on the rough surface. 相似文献
59.
Poly(2-methoxy-5-[2′-ethylhexyoxy]-1,4-phenylenevinylene) (MEHPPV) derivatives with polyacrylic acid (PAA) chains grafted
onto their backbone were found to be water soluble, and they exhibited a dramatic increase in their fluorescence intensity
in the presence of a variety of surfactants, even at concentrations far below their critical micelle concentrations (CMC).
This increase was accompanied by a blue-shift in the emission maximum. These observations are rationalized based on the postulate
that the backbone conformation of the conjugated polymer is modulated upon interaction of the surfactant molecules with the
polyelectrolytic tethers, which in turn results in a significant depletion of intra-chain interchromophore interactions that
are known to cause red-shifted emission bands with significantly lower emission yields. 相似文献
60.