Zeptonewton force sensing with nanospheres in an optical lattice

Optically trapped nanospheres in high-vaccum experience little friction and hence are promising for ultra-sensitive force detection. Here we demonstrate measurement times exceeding $10^5$ seconds and zeptonewton force sensitivity with laser-cooled silica nanospheres trapped in an optical lattice. The sensitivity achieved exceeds that of conventional room-temperature solid-state force sensors, and enables a variety of applications including electric field sensing, inertial sensing, and gravimetry. The optical potential allows the particle to be confined in a number of possible trapping sites, with precise localization at the anti-nodes of the optical standing wave. By studying the motion of a particle which has been moved to an adjacent trapping site, the known spacing of the lattice anti-nodes can be used to calibrate the displacement spectrum of the particle. Finally, we study the dependence of the trap stability and lifetime on the laser intensity and gas pressure, and examine the heating rate of the particle in high vacuum in the absence of optical feedback cooling.Comment: 5 pages, 4 figures, minor changes, typos corrected, references adde

First principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device

We have elaborately studied the electronic structure of 555-777 divacancy (DV) defected armchair edged graphene nanoribbon (AGNR) and transport properties of AGNR based two-terminal device constructed with one defected electrode and one N doped electrode, by using density functional theory and non-equilibrium Green's function based approach. The introduction of 555-777 DV defect into AGNRs, results in a shifting of the {\pi} and {\pi}* bands towards the higher energy value which indicates a shifting of the Fermi level towards the lower energy. Formation of a potential barrier, very similar to that of conventional p-n junction, has been observed across the junction of defected and N doped AGNR. The prominent asymmetric feature of the current in the positive and negative bias indicates the diode like property of the device with high rectifying efficiency within wide range of bias voltages. The device also shows robust negative differential resistance (NDR) with very high peak-to-valley ratio. The analysis of the shifting of the energy states of the electrodes and the modification of the transmission function with applied bias provides an insight into the nonlinearity and asymmetry observed in the I-V characteristics. Variation of the transport properties on the width of the ribbon has also been discussed.Comment: 28 Pages, 12 Figures and 1 tabl

Origin of negative differential resistance in a strongly coupled single molecule-metal junction device

A new mechanism is proposed to explain the origin of negative differential resistance (NDR) in a strongly coupled single molecule-metal junction. A first-principles quantum transport calculation in a Fe-terpyridine linker molecule sandwiched between a pair of gold electrodes is presented. Upon increasing applied bias, it is found that a new phase in the broken symmetry wavefunction of the molecule emerges from the mixing of occupied and unoccupied molecular orbital. As a consequence, a non-linear change in the coupling between molecule and lead is evolved resulting to NDR. This model can be used to explain NDR in other class of metal-molecule junction device.Comment: Submitted for review on Feb 4, 200

Antimicrobial Activity of Selected Medicinal Plants, \u3cem\u3eCraetva magna\u3c/em\u3e (Linn.), \u3cem\u3ePongamia glabra\u3c/em\u3e (Linn.) and \u3cem\u3eAreca catechu\u3c/em\u3e (Linn.)

Antimicrobial potential in the extracts of three plants. viz. Craetva magna (Linn.), Pongamia glabra (Linn.), Areca catechu (Linn.) that are commonly used by the Kani Tribes of Tirunelveli district, was traced in the present study. The extract of the plant Craetva magna (Linn.), inhibited the growth of pathogenic microbes. Soxhlet extract using chloroform as solvent showed a maximum inhibition of zone formation for the species Salmonella paratyphi (14 mm), and Vibrio cholerae (13 mm) at a concentration of 50 µg/ml. The crude extract of the plant Pongamia glabra (Linn.), showed maximum inhibition for the species Salmonella paratyphi (8 mm), and Vibrio fischeri (8mm) at the concentration of 50 µg/ml. In the Soxhlet-chloroform extract, of Areca catechu the maximum inhibition zone was observed for Vibrio cholerae (14 mm), and Salmonella paratyphi (13 mm). In the present study it was observed that the extracts of the bark of the Craetva magna (Linn.), Pongamia glabra (Linn.), Areca catechu (Linn.), had a broad spectrum antifungal activity

Temperature Dependence Quantum State of Electron in One Dimensional Carbon Nano Tubes and The Expression for Temperature Co-efficient of Resistance in Terms of Quantum State

The Field of Carbon nano tube (CNT) is an promising area of research theoretically as well as experimentally [1],[2]. In fact the band structure of CNT determines its conductivity and in carbon nano tubes the structural pattern affects the conductivity type i.e the conductivity of CNT depends upon how graphene sheet is rolled up. So, CNT can be made to behave as conductor as well as semiconductor [2] It is well established that the samples of single wall carbon nano tubes with an arm chair wrapping have been produced and exhibit metallic behavior with an intrinsic resistivity which increases approximately linearly with temperature over a wide temperature range (see for instance ref.[4]. In this paper the quantized value of electric conductivity [1],[2] is used in an attempt to show theoretically that the quantum state of the electron of the carbon nano tube is directly related to temperature of the CNT as resistivity of CNT depends on quantum state and also found to depend on temperature. Finally, an effort has been made to find an approximatenbsp expression for the temperature co-efficient of resistance of the CNT