Wide-band current preamplifier for conductance measurements with large input capacitance

A wide-band current preamplifier based on a composite operational amplifier is proposed. It has been shown that the bandwidth of the preamplifier can be significantly increased by enhancing the effective open-loop gain of the composite preamplifier. The described preamplifier with current gain 10$^7$ V/A showed the bandwidth of about 100 kHz with 1 nF input shunt capacitance. The current noise of the amplifier was measured to be about 46 fA/$\sqrt{\rm Hz}$ at 1 kHz, close to the design noise minimum. The voltage noise was found to be about 2.9 nV/$\sqrt{\rm Hz}$ at 1 kHz, which is in a good agreement with the value expected for the operational amplifier used in the input stage. By analysing the total noise produced by the preamplifier we found the optimal frequency range suitable for the fast lock-in measurements to be from 1 kHz to 2 kHz. To get the same signal-to-noise ratio, the reported preamplifier requires roughly 10% of the integration time used in measurements made with a conventional preamplifier.Comment: 5 pages, 4 figure

Effects of a Novel Dental Gel on Plaque and Gingivitis: A Comparative Study.

ObjectivesThe goal of this prospective, randomized, controlled, double-blinded study was to evaluate the effects of a novel dental gel on plaque and gingival health. The dental gel was designed to (1) break up and prevent re-accumulation of microbial biofilm, and (2) inhibit metal mediated inflammation.Materials and methodsTwenty-five subjects with moderate gingival inflammation (Löe and Silness Gingival Index ≥2) and pocket depths <4 were randomly assigned to brush twice daily for 21 days with the test or the control dental gel. On Days 0, 7, 14 and 21, plaque levels (Quigley-Hein, Turesky Modification Plaque Index), gingival inflammation (Löe and Silness Gingival Index) and gingival bleeding (modified Sulcus Bleeding Index) were determined by one blinded, investigator using a pressure sensitive probe.ResultsAfter 3 weeks, all 3 clinical indices were significantly improved in both groups (P<0.05) and significantly lower in the test group (P<0.05).ConclusionThe novel dental gel formulation was provided effective plaque control and reduced gingival inflammation.Clinical relevanceA novel dentifrice formulation may be an effective tool for plaque removal and maintaining gingival health

Competing topological and Kondo insulator phases on a honeycomb lattice

We investigate the competition between the spin-orbit interaction of itinerant electrons and their Kondo coupling with local moments densely distributed on the honeycomb lattice. We find that the model at half-filling displays a quantum phase transition between topological and Kondo insulators at a nonzero Kondo coupling. In the Kondo-screened case, tuning the electron concentration can lead to a new topological insulator phase. The results suggest that the heavy-fermion phase diagram contains a new regime with a competition among topological, Kondo-coherent and magnetic states, and that the regime may be especially relevant to Kondo lattice systems with $5d$-conduction electrons. Finally, we discuss the implications of our results in the context of the recent experiments on SmB$_6$ implicating the surface states of a topological insulator, as well as the existing experiments on the phase transitions in SmB$_6$ under pressure and in CeNiSn under chemical pressure.Comment: (v3) Published version including the main text (5 pages + 4 figures) and a supplementary material discussing the effects of quantum fluctuations of the slave bosons and antiferromagnetic ordering of the local moments on the transitions among the Kondo, magnetic and topological state

On the chain length dependence of local correlations in polymer melts and a perturbation theory of symmetric polymer blends

The self-consistent field (SCF) theory of dense polymer liquids assumes that short-range correlations are almost independent of how monomers are connected into polymers. Some limits of this idea are explored in the context of a perturbation theory for mixtures of structurally identical polymer species, A and B, in which the AB pair interaction differs slightly from the AA and BB interaction, and the difference is controlled by a parameter alpha Expanding the free energy to O(\alpha) yields an excess free energy of the form alpha $z(N)\phi_{A}\phi_{B}$, in both lattice and continuum models, where z(N) is a measure of the number of inter-molecular near neighbors of each monomer in a one-component liquid. This quantity decreases slightly with increasing N because the self-concentration of monomers from the same chain is slightly higher for longer chains, creating a deeper correlation hole for longer chains. We analyze the resulting $N$-dependence, and predict that $z(N) = z^{\infty}[1 + \beta \bar{N}^{-1/2}]$, where $\bar{N}$ is an invariant degree of polymerization, and $\beta=(6/\pi)^{3/2}$. This and other predictions are confirmed by comparison to simulations. We also propose a way to estimate the effective interaction parameter appropriate for comparisons of simulation data to SCF theory and to coarse-grained theories of corrections to SCF theory, which is based on an extrapolation of coefficients in this perturbation theory to the limit $N \to \infty$. We show that a renormalized one-loop theory contains a quantitatively correct description of the $N$-dependence of local structure studied here.Comment: submitted to J. Chem. Phy

Kondo effect in coupled quantum dots with RKKY interaction: Finite temperature and magnetic field effects

We study transport through two quantum dots coupled by an RKKY interaction as a function of temperature and magnetic field. By applying the Numerical Renormalization Group (NRG) method we obtain the transmission and the linear conductance. At zero temperature and magnetic field, we observe a quantum phase transition between the Kondo screened state and a local spin singlet as the RKKY interaction is tuned. Above the critical RKKY coupling the Kondo peak is split. However, we find that both finite temperature and magnetic field restore the Kondo resonance. Our results agree well with recent transport experiments on gold grain quantum dots in the presence of magnetic impurities.Comment: 4 pages, 5 figure

Acoustically evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach

It is still a matter of debate whether cephalopods can detect sound frequencies above 400 Hz. So far there is no proof for the detection of underwater sound above 400 Hz via a physiological approach. The controversy of whether cephalopods have a sound detection ability above 400 Hz was tested using the auditory brainstem response (ABR) approach, which has been successfully applied in fish, crustaceans, amphibians, reptiles and birds. Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz (Octopus vulgaris), respectively. The thresholds of S. lessoniana were generally lower than those of O. vulgaris

Two-stage Kondo effect in side-coupled quantum dots: Renormalized perturbative scaling theory and Numerical Renormalization Group analysis

We study numerically and analytically the dynamical (AC) conductance through a two-dot system, where only one of the dots is coupled to the leads but it is also side-coupled to the other dot through an antiferromagnetic exchange (RKKY) interaction. In this case the RKKY interaction gives rise to a ``two-stage Kondo effect'' where the two spins are screened by two consecutive Kondo effects. We formulate a renormalized scaling theory that captures remarkably well the cross-over from the strongly conductive correlated regime to the low temperature low conductance state. Our analytical formulas agree well with our numerical renormalization group results. The frequency dependent current noise spectrum is also discussed.Comment: 6 pages, 7 figure