Lei Wang

Thermal memory: a storage of phononic information.

Memory is an indispensible element for a computer in addition to logic gates. In this Letter we report a model of thermal memory. We demonstrate via numerical simulation that thermal (phononic) information stored in the memory can be retained for a long time without being lost and more importantly can be read out without being destroyed. The possibility of experimental realization is also discussed.

In vitro cancer cell imaging and therapy using transferrin-conjugated gold nanoparticles

Gold nanoparticles were conjugated with transferrin molecules for targeting, imaging and therapy of breast cancer cells (Hs578T, ATCC). Results show that, the transferrin-transferrin receptor-mediated cellular uptake of gold nanoparticles is six times of that in the absence of this interaction. As a consequence, the laser power effective for photothermal therapy of the cancer cells was reduced to values of two orders of magnitude lower. To demonstrate the efficiency of the conjugated gold nanoparticles in selectively targeting cancer cells, the cellular uptake of the gold nanoparticles by noncancerous cells (3T3, ATCC) was also investigated. The cellular uptake by the normal cells is only one fourth of that by the cancerous cells indicating that the transferrin-transferrin receptor interaction plays an important role in controlling the cellular uptake of the gold nanoparticles.

Interface Thermal Resistance between Dissimilar Anharmonic Lattices

We study interface thermal resistance (ITR) in a system consisting of two dissimilar anharmonic lattices exemplified by the Fermi-Pasta-Ulam and Frenkel-Kontorova models. It is found that the ITR is asymmetric; namely, it depends on how the temperature gradient is applied. The dependence of the ITR on the coupling constant, temperature, temperature difference, and system size is studied. Possible applications in nanoscale heat management and control are discussed.

Amine‐Catalyzed [3+2] Huisgen Cycloaddition Strategy for the Efficient Assembly of Highly Substituted 1,2,3‐Triazoles

An enamine-catalyzed strategy has been utilized to fully promote the Huisgen [3+2] cycloaddition with a broad spectrum of carbonyl compounds and azides, thereby permitting the efficient assembly of a vast pool of highly substituted 1,2,3-triazoles. In particular, the employment of commonly used and commercially available carbonyl compounds has resulted in the introduction of a diverse set of functional groups, such as alkyl, aryl, nitrile, ester, and ketone groups, at the 1-, 4-, or 5-positions of the 1,2,3-triazole scaffold. This approach might be manipulated to access more useful and sophisticated heterocyclic compounds. Most significantly, the reaction process exhibits complete regioselectivity, with the formation of only one regioisomer.

Enantioselective Synthesis of Coumarins Catalyzed by a Bifunctional Amine–Thiourea Catalyst

The development of asymmetric methods for the preparation of functionalized coumarins has been of long-standing interest to organic chemists. As a result of their broad applications in organic synthesis they are widely distributed in a vast array of bioactive molecules. Warfarin (see below) has been discovered as an anticoagulant, inhibiting Vitamin K epoxide reductase and thereby decreasing blood coagulation by preventing the vitamin K dependent synthesis of bloodclotting proteins. Bromadiolone is a second-generation 4hydroxycoumarin derivative, called as a “super-warfarin” for its added potency and tendency to accumulate in the liver of the poisoned organism. It was effective against the populations that had become resistant to the first-generation anticoagulants. Phenprocoumon is another anticoagulant drug

Finite Thermal Conductivity in 1D Models Having Zero Lyapunov Exponents

Heat conduction in three types of 1D channels is studied. The channels consist of two parallel walls, right triangles as scattering obstacles, and noninteracting particles. The triangles are placed along the walls in three different ways: (i) periodic, (ii) disordered in height, and (iii) disordered in position. The Lyapunov exponents in all three models are zero because of the flatness of triangle sides. It is found numerically that the temperature gradient can be formed in all three channels, but the Fourier heat law is observed only in two disordered ones. The results show that there might be no direct connection between chaos (in the sense of positive Lyapunov exponent) and normal thermal conduction.

Anomalous heat conduction and anomalous diffusion in nonlinear lattices, single walled nanotubes, and billiard gas channels

We study anomalous heat conduction and anomalous diffusion in low-dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is sigma(2)(t)=2Dt(alpha) (0<alpha< or =2), then the thermal conductivity can be expressed in terms of the system size L as kappa=cL(beta) with beta=2-2/alpha. This result predicts that a normal diffusion (alpha=1) implies a normal heat conduction obeying the Fourier law (beta=0), a superdiffusion (alpha>1) implies an anomalous heat conduction with a divergent thermal conductivity (beta>0), and more interestingly, a subdiffusion (alpha<1) implies an anomalous heat conduction with a convergent thermal conductivity (beta<0), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our theoretical prediction.

Highly Regioselective Organocatalyzed Synthesis of Pyrazoles from Diazoacetates and Carbonyl Compounds

A general, organocatalytic inverse-electron-demand [3+2] cycloaddition reaction between a range of carbonyl compounds and diazoacetates has been developed. This reaction is catalyzed by secondary amines as a green promoter to generate substituted pyrazoles with high levels of regioselectivity. It is noteworthy that this [3+2] cycloaddition reaction proceeds efficiently at room temperature with a simple and inexpensive catalyst. Considering the large variety and ready availability of the starting materials (e.g. ketones, β-ketoesters, β-diketones, and aldehydes), as well as the operational simplicity of this process, a convenient, practical, and highly modular pyrazole synthesis has been developed. We believe that this work will arouse more research interest in the organocatalytic synthesis of other biologically active heterocycles. Such studies are currently underway in our laboratory.

Direct Access to Highly Substituted 1‐Naphthols through Palladium‐Catalyzed Oxidative Annulation of Benzoylacetates and Internal Alkynes

One for the pot: 1-Naphthols, well-known structural design elements in medicinal chemistry, were readily prepared by means of a one-pot palladium-catalyzed oxidative annulation of readily available benzoylacetates to internal alkynes.

Cellular automaton traffic flow model between the Fukui-Ishibashi and Nagel-Schreckenberg models.

We propose and study a one-dimensional traffic flow cellular automaton model of high-speed vehicles with the Fukui-Ishibashi-type acceleration for all cars, and the Nagel-Schreckenberg-type (NS) stochastic delay only for cars following the trail of the car ahead. The main difference in the delay scenario between our model and the NS model is that a car with spacing ahead longer than the velocity limit M may not be delayed in our model. By using a car-oriented mean-field theory, we analytically derive fundamental diagrams of the average speed as a function of the car density. Our theoretical results are in excellent agreement with numerical simulations.