Experimental demonstration of stimulated polarization wave in a chain of nuclear spins

A stimulated wave of polarization, which implements a simple mechanism of quantum amplification, is experimentally demonstrated in a chain of four J-coupled nuclear spins, irradiated by a weak radio-frequency transverse field. The "quantum domino" dynamics, a wave of flipped spins triggered by a flip of the first spin, has been observed in fully $^{13}$C-labeled sodium butyrate.Comment: 8 pages including 3 figure

Conformations and charge transport characteristics of biphenyldithiol self-assembled-monolayer molecular electronic devices: A multiscale computational study

We report a computational study of conformations and charge transport characteristics of biphenyldithiol (BPDT) monolayers in the (sqrt(3)×sqrt(3))R30° packing ratio sandwiched between Au(111) electrodes. From force-field molecular-dynamics and annealing simulations of BPDT self-assembled monolayers (SAMs) with up to 100 molecules on a Au(111) substrate, we identify an energetically favorable herringbone-type SAM packing configuration and a less-stable parallel packing configuration. Both SAMs are described by the (2sqrt(3)×sqrt(3))R30° unit cell including two molecules. With subsequent density-functional theory calculations of one unit cell of the (i) herringbone SAM with the molecular tilt angle theta[approximate]15°, (ii) herringbone SAM with theta[approximate]30°, and (iii) parallel SAM with theta[approximate]30°, we confirm that the herringbone packing configuration is more stable than the parallel one but find that the energy variation with respect to the molecule tilting within the herringbone packing is very small. Next, by capping these SAMs with the top Au(111) electrode, we prepare three molecular electronic device models and calculate their coherent charge transport properties within the matrix Green's function approach. Current–voltage (I–V) curves are then obtained via the Landauer–Büttiker formula. We find that at low-bias voltages (|V|~0.5 V), the I–V characteristics of the three models show noticeable differences due to different phenyl band structures. We thus conclude that the BPDT SAM I–V characteristics in the low-bias voltage region are mainly determined by the Si–Au interaction within the individual molecule-electrode contact, while both intramolecular conformation and intermolecular interaction can affect the BPDT SAM I–V characteristics in the high-bias voltage region

Zeolitic Imidazolate Frameworks as H_2 Adsorbents: Ab Initio Based Grand Canonical Monte Carlo Simulation

We report the H_2 uptake behavior of 10 zeolitic−imidazolate frameworks (ZIFs), based on grand canonical Monte Carlo (GCMC) simulations. The force fields (FFs) describing the interactions between H_2 and ZIF in the GCMC were based on ab initio quantum mechanical (QM) calculations (MP2) aimed at correctly describing London dispersion (van der Waals attraction). Thus these predictions of H_2 uptake are based on first principles (non empirical) and hence applicable to new framework materials for which there is no empirical data. For each of these 10 ZIFs we report the total and excess H_2 adsorption isotherms up to 100 bar at both 77 and 300 K. We report the hydrogen adsorption sites in the ZIFs and the relationships between H_2 uptake amount, isosteric heat of adsorption (Q_(st)), surface area, and free volume. Our simulation shows that various ZIFs lead to a variety of H_2 adsorption behaviors in contrast to the metal−organic frameworks (MOFs). This is because ZIFs leads to greater diversity in the adsorption sites (depending on both organic linkers and zeolite topologies) than in MOFs. In particular, the ZIFs uptake larger amounts of H_2 at low pressure because of the high H_2 adsorption energy, and ZIFs have a variety of H_2 adsorption sites. For example, ZIF-11 has an initial Q_(st) value of ~15 kJ/mol, which is higher than observed for MOFs. Moreover, the preferential H_2 adsorption site in ZIFs is onto the organic linker, not nearby the metallic joint as is the case for MOFs

Possible performance improvement in [2]catenane molecular electronic switches

Mechanically interlocked bistable supramolecular complexes are promising candidates of molecular electronics. Applying a multiscale computational approach, here we study the coherent charge transport properties of catenane monolayers sandwiched between Cu(111) electrodes. We demonstrate the robust nature of electrical switching behavior with respect to the variations in the monolayer packing density and the type of electrodes, as well as the thermal fluctuations of the molecules. We propose that the asymmetry of molecule-electrode barriers can be utilized to improve the switching ratio

Comparison of transjugular intrahepatic portosystemic shunt with covered stent and balloon-occluded retrograde transvenous obliteration in managing isolated gastric varices

OBJECTIVE: Although a transjugular intrahepatic portosystemic shunt (TIPS) is commonly placed to manage isolated gastric varices, balloon-occluded retrograde transvenous obliteration (BRTO) has also been used. We compare the long-term outcomes from these procedures based on our institutional experience. MATERIALS AND METHODS: We conducted a retrospective review of patients with isolated gastric varices who underwent either TIPS with a covered stent or BRTO between January 2000 and July 2013. We identified 52 consecutive patients, 27 who had received TIPS with a covered stent and 25 who had received BRTO. We compared procedural complications, re-bleeding rates, and clinical outcomes between the two groups. RESULTS: There were no significant differences in procedural complications between patients who underwent TIPS (7%) and those who underwent BRTO (12%) (p = 0.57). There were also no statistically significant differences in re-bleeding rates from gastric varices between the two groups (TIPS, 7% [2/27]; BRTO, 8% [2/25]; p = 0.94) or in developing new ascites following either procedure (TIPS, 4%; BRTO, 4%; p = 0.96); significantly more patients who underwent TIPS developed hepatic encephalopathy (22%) than did those who underwent BRTO (0%, p = 0.01). There was no statistically significant difference in mean survival between the two groups (TIPS, 30 months; BRTO, 24 months; p = 0.16); median survival for the patients who received TIPS was 16.6 months, and for those who underwent BRTO, it was 26.6 months. CONCLUSION: BRTO is an effective method of treating isolated gastric varices with similar outcomes and complication rates to those of TIPS with a covered stent but with a lower rate of hepatic encephalopathy

Boundary correlation function of fixed-to-free bcc operators in square-lattice Ising model

We calculate the boundary correlation function of fixed-to-free boundary condition changing operators in the square-lattice Ising model. The correlation function is expressed in four different ways using $2\times2$ block Toeplitz determinants. We show that these can be transformed into a scalar Toeplitz determinant when the size of the matrix is even. To know the asymptotic behavior of the correlation function at large distance we calculate the asymptotic behavior of this scalar Toeplitz determinant using the Szeg\"o's theorem and the Fisher-Hartwig theorem. At the critical temperature we confirm the power-law behavior of the correlation function predicted by conformal field theory