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101.
The Landauer-type formulation of current through a molecular junction with electronic-nuclear coupling introduced by Troisi et al. [J. Chem. Phys. 118, 6072 (2003)] is generalized to account for the dependence of the molecule-leads coupling terms on the nuclear coordinates. Although this electronic-nuclear coupling is external to the molecule there is no need to extend the molecular subspace when projection operators are employed for calculations of the current through the junction. A test case of a conductor with vibrating contacts to the leads is studied numerically. It is demonstrated that contact vibrations lead to inelastic contributions to the current and to characteristic features in the I-V curve and its derivatives, similar to the ones observed for internal (molecular) electronic-nuclear coupling. 相似文献
102.
103.
Noel D. Uri 《Applied Mathematical Modelling》1977,1(5):253-256
This paper applies a translog model to a pooled sample in order to measure the extent of regional interfuel substitution effects in the electric power industry. The results obtained indicate that relative changes in fuel prices both regionally and nationally have significant effects on fossil fuel consumption. This, in turn, has important implications for public policy. In particular, the market system appears better able to deal with exogenous shifts in energy supplies than has frequently been assumed in the formulation of public policies toward the energy crisis.Further, compared to aggregate United States time series estimates, a more elastic fuel price response is found thus questioning whether full long-run adjustment is being measured in the pure time series estimates. Given the importance of the latter in energy tax policy analysis for example, the question is indeed more than academic. 相似文献
104.
A new approach for solving the laminar flow problem above a porous medium is presented here, using an apparent interface for
which both superficial velocity and intrinsic shear stress are continuous. The derivation of this approach is based on a detailed
investigation of the Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer 38:2635–2646, 1995a) jump condition and its sensitivity
to the value of β (the jump condition coefficient) and to an error in the interface location. While the value of the jump
condition coefficient is highly sensitive to the interface location, the new apparent interface approach does not require
an a priori information about the location of the interface. This approach can be easily used knowing only one measurable
parameter—the maximum velocity or the flow rate. Validation of the apparent interface approach against measurements from other
works shows that it can be successfully used to predict the velocity profile for different geometrical models. 相似文献
105.
Pratim Sengupta Uri Wilensky 《International Journal of Computers for Mathematical Learning》2009,14(1):21-50
Electricity is regarded as one of the most challenging topics for students of all ages. Several researchers have suggested
that na?ve misconceptions about electricity stem from a deep incommensurability (Slotta and Chi 2006; Chi 2005) or incompatibility (Chi et al.
1994) between na?ve and expert knowledge structures. In this paper we argue that adopting an emergent levels-based perspective
as proposed by Wilensky and Resnick (1999), allows us to reconceive commonly noted misconceptions in electricity as behavioral evidences of “slippage between levels,”
i.e., these misconceptions appear when otherwise productive knowledge elements are sometimes activated inappropriately due
to certain macro-level phenomenological cues only. We then introduce NIELS (NetLogo Investigations In Electromagnetism), a
curriculum of emergent multi-agent-based computational models. NIELS models represent phenomena such as electric current and
resistance as emergent from simple, body-syntonic interactions between electrons and other charges in a circuit. We discuss results from a pilot
implementation of NIELS in an undergraduate physics course, that highlight the ability of an emergent levels-based approach
to provide students with a deep, expert-like understanding of the relevant phenomena by bootstrapping, rather than discarding their existing repertoire of intuitive knowledge.
相似文献
Pratim SenguptaEmail: |
106.
107.
Uri Stoin Dr. Alexander I. Shames Itamar Malka Prof. Ilana Bar Prof. Yoel Sasson 《Chemphyschem》2013,14(18):4158-4164
In the recent decades superoxide [O2?.] has become the subject of considerable interest. Nonetheless, generation of superoxide compounds is still a substantial challenge. The standard methods for synthesis of superoxide derivatives are either through the oxidation of molten alkali metals with hot air or by using electrolytic reduction of oxygen in aprotic solvent such as dimethylformamide. No methodology is available for the generation of superoxides in protic solutions and particularly not in water. We propose a new in situ method for alkali superoxide preparation by using sodium hydroxide and hydrogen peroxide at room temperature and in aqueous solution. 相似文献
108.
Gill R Freeman R Xu JP Willner I Winograd S Shweky I Banin U 《Journal of the American Chemical Society》2006,128(48):15376-15377
CdSe/ZnS QDs enable the optical probing of the biocatalytic oxidation of tyrosine derivatives and of the scission of peptides by thrombin. CdSe/ZnS QDs were modified with tyrosine methyl ester or with a tyrosine-containing peptide. The tyrosine units were reacted with tyrosinase/O2 to yield the respective l-DOPA and quinone derivatives. The luminescence of QDs modified by the enzyme-generated quinone units is quenched. The quinone-functionalized peptide associated with the QDs was cleaved by thrombin, a process that restored the luminescence of the QDs. 相似文献
109.
A model for electron transfer in donor-bridge-acceptor complexes with electronic coupling to nuclear bridge modes is studied using the Redfield formulation. We demonstrate that the transport mechanism through the molecular bridge is controlled by the location of the electronic-nuclear coupling term along the bridge. As the electronic-nuclear coupling term is shifted from the donor/acceptor-bridge contact sites into the bridge, the mechanism changes from kinetic transport (incoherent, thermally activated, and bridge-length independent) to coherent tunneling oscillations. This study joins earlier works aiming to explore the factors which control the mechanism of electronic transport through molecular bridges and molecular wires. 相似文献
110.
Scolnik Y Portnaya I Cogan U Tal S Haimovitz R Fridkin M Elitzur AC Deamer DW Shinitzky M 《Physical chemistry chemical physics : PCCP》2006,8(3):333-339
Mirror-image asymmetric molecules, i.e., chiral isomers or enantiomers, are classically considered as chemically identical. Recent studies, however, have indicated that parity violation by the nuclear weak force induces a tiny energy difference between chiral isomers. Upon combination with a massive amplification process, expansion of this difference to a detectable macroscopic level may be achieved. Yet, experimental tests of this possibility, where one enantiomer is compared to the other in solution, are hampered by the possible presence of undetectable impurities. In this study we have overcome this problem by comparing structural and dynamic features of synthetic D- and L-polyglutamic acid and polylysine molecules each of 24 identical residues. In these water-soluble polypeptides helix formation is an intramolecular autocatalytic process amplified by each turn, which is actually unaffected by low level of putative impurities in the solvent. The helix and random coil configurations and their transition were determined in this study by circular dichroism (CD) and isothermal titration calorimetry (ITC) in water and deuterium oxide. Distinct differences in structure and transition energies between the enantiomeric polypeptides were detected by both CD and ITC when dissolved in water. Intriguingly, these differences were by and large abolished in deuterium oxide. Our findings suggest that deviation from physical invariance between the D- and L-polyamino acids is induced in part by different hydration in water which is eliminated in deuterium oxide. Based on the recent findings by Tikhonov and Volkov (V. I. Tikhonov and A. A. Volkov, Science 2002, 296, 2363) we suggest that ortho-H(2)O, which constitutes 75% of bulk H(2)O, has a preferential affinity to L-enantiomers. Differential hydration of enantiomers may have played a role in the selection of L-amino acids by early forms of life. 相似文献