Electron transport through a quantum interferometer with side-coupled quantum dots: Green's function approach

We study electron transport through a quantum interferometer with side-coupled quantum dots. The interferometer, threaded by a magnetic flux $\phi$, is attached symmetrically to two semi-infinite one-dimensional metallic electrodes. The calculations are based on the tight-binding model and the Green's function method, which numerically compute the conductance-energy and current-voltage characteristics. Our results predict that under certain conditions this particular geometry exhibits anti-resonant states. These states are specific to the interferometric nature of the scattering and do not occur in conventional one-dimensional scattering problems of potential barriers. Most importantly we show that, such a simple geometric model can also be used as a classical XOR gate, where the two gate voltages, viz, $V_a$ and $V_b$, are applied, respectively, in the two dots those are treated as the two inputs of the XOR gate. For $\phi=\phi_0/2$ ($\phi_0=ch/e$, the elementary flux-quantum), a high output current (1) (in the logical sense) appears if one, and only one, of the inputs to the gate is high (1), while if both inputs are low (0) or both are high (1), a low output current (0) appears. It clearly demonstrates the XOR gate behavior and this aspect may be utilized in designing the electronic logic gate.Comment: 8 pages, 5 figure

Charge-transfer induced large nonlinear optical properties of small Al Clusters: Al4M4

We investigate the linear and nonlinear electric polarizabilities of small Al4M4 (M=Li, Na and K) clusters. Quantum chemical calculations reveal that these compounds exhibit an exceptionally high magnitude of linear and nonlinear optical (NLO) coefficients which are orders of magnitude higher than the conventional pi-conjugated systems of similar sizes. We attribute such phenomenal increase to non-centrosymmetricity incorporated in the systems by the alkali atoms surrounding the ring leading to charge transfer with small optical gap and low bond length alternation (BLA). Such a low magnitude of the BLA from a different origin, suggests the possibility that these clusters are aromatic in character and along with the large NLO coefficients they appear to be better candidates for next generation NLO fabrication devices

NAND gate response in a mesoscopic ring: An exact study

NAND gate response in a mesoscopic ring threaded with a magnetic flux $\phi$ is investigated by using Green's function formalism. The ring is attached symmetrically to two semi-infinite one-dimensional metallic electrodes and two gate voltages, namely, $V_a$ and $V_b$, are applied in one arm of the ring those are treated as the two inputs of the NAND gate. We use a simple tight-binding model to describe the system and numerically compute the conductance-energy and current-voltage characteristics as functions of the gate voltages, ring-to-electrode coupling strength and magnetic flux. Our theoretical study shows that, for $\phi=\phi_0/2$ ($\phi_0=ch/e$, the elementary flux-quantum) a high output current (1) (in the logical sense) appears if one or both the inputs to the gate are low (0), while if both the inputs to the gate are high (1), a low output current (0) appears. It clearly exhibits the NAND gate behavior and this feature may be utilized in designing an electronic logic gate.Comment: 8 pages, 5 figure

Productivity, profitability and income distribution in capture fishery - a case study in Orissa coast

In the literature on marine and inland fisheries very little attention has been focused on income generation by various craft-gear combinations, their productivity and the extent, nature and causes of fluctuations in their incomes. This study of the Orissa coast explores the consequences of mechanisation on income distribution between mechanised and non-mechanised fishing units

On the production mechanism of radio-pulses from large extensive air showers

None of the theories put forward so far to explain the radio emission from cosmic ray showers, has been successful in giving a satisfactory explanation for all the experimental data obtained from various laboratories over the globe. It is apprehended that emission mechanism at low and high frequencies may be quite different. This calls for new theoretical look into the phenomenon. Theoretical as well as the experimental results indicate that the frequency spectrum is rather flat in the frequency range (40 to 60 MHz. Above 80 MHz, the radio emission can be explained with the help of geomagnetic mechanism. But at very low frequency ( 10 MHz), mechanisms other than geomagnetic are involved