Cavity QED with semiconductor nanocrystals

We report on a strongly coupled cavity quantum electrodynamic (CQED) system consisting of a CdSe nanocrystal coupled to a single photon mode of a polymer microsphere. The strong exciton-photon coupling is manifested by the observation of a cavity mode splitting variant Planck's over 2piOmega(exp) between 30 und 45 microeV and photon lifetime measurements of the coupled exciton-photon state. The single photon mode is isolated by lifting the mode degeneracy in a slightly deformed microsphere cavity and addressing it by high-resolution imaging spectroscopy. This cavity mode is coupled to a localized exciton of an anisotropically shaped CdSe nanocrystal that emits highly polarized light in resonance to the cavity mode and that was placed in the maximum electromagnetic field close to the microsphere surface. The exciton confined in the CdSe nanorod exhibits an optical transition dipole moment much larger than that of atoms, the standard system for CQED experiments, and a low-temperature homogeneous line width much narrower than the high-Q cavity mode width. The observation of strong coupling in a colloidal semiconductor nanocrystal-cavity system opens the way to study fundamental quantum-optics phenomena and to implement quantum information processing concepts that work in the visible spectral range and are based on solid-state nanomaterials.     

Cationic liposome-DNA complexes: from liquid crystal science to gene delivery applications

At present, there is an unprecedented level of interest in the properties and structures of complexes consisting of DNA mixed with oppositely charged cationic liposomes (CLs). The interest arises because the complexes mimic natural viruses as chemical carriers of DNA into cells in worldwide human gene therapy clinical trials. However, since our understanding of the mechanisms of action of CL-DNA complexes interacting with cells remains poor, significant additional insights and discoveries will be required before the development of efficient chemical carriers suitable for long-term therapeutic applications. Recent studies describe synchrotron X-ray diffraction, which has revealed the liquid crystalline nature of CL-DNA complexes, and three-dimensional laser-scanning confocal microscopy, which reveals CL-DNA pathways and interactions with cells. The importance of the liquid crystalline structures in biological function is revealed in the application of these modern techniques in combination with functional transfection efficiency measurements, which shows that the mechanism of gene release from complexes in the cell cytoplasm is dependent on their precise liquid crystalline nature and the physical and chemical parameters (for example, the membrane charge density) of the complexes. In [section sign] 5, we describe some recent new results aimed at developing bionanotube vectors for gene delivery.     

Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods

Dimensionality and size are two factors that govern the properties of semiconductor nanostructures. In nanocrystals, dimensionality is manifested by the control of shape, which presents a key challenge for synthesis. So far, the growth of rod-shaped nanocrystals using a surfactant-controlled growth mode, has been limited to semiconductors with wurtzite crystal structures, such as CdSe (ref. 3). Here, we report on a general method for the growth of soluble nanorods applied to semiconductors with the zinc-blende cubic lattice structure. InAs quantum rods with controlled lengths and diameters were synthesized using the solution-liquid-solid mechanism with gold nanocrystals as catalysts. This provides an unexpected link between two successful strategies for growing high-quality nanomaterials, the vapour-liquid-solid approach for growing nanowires, and the colloidal approach for synthesizing soluble nanocrystals. The rods exhibit both length- and shape-dependent optical properties, manifested in a red-shift of the bandgap with increased length, and in the observation of polarized emission covering the near-infrared spectral range relevant for telecommunications devices.     

Shallow circuits and concise formulae for multiple addition and multiplication

A theory is developed for the construction of carry-save networks with minimal delay, using a given collection of carry-save adders each of which may receive inputs and produce outputs using several different representation standards.The construction of some new carry-save adders is described. Using these carry-save adders optimally, as prescribed by the above theory, we get {, , }-circuits of depth 3.48 log₂ n and {, , }-circuits of depth 4.95 log₂ n for the carry-save addition ofn numbers of arbitrary length. As a consequence we get multiplication circuits of the same depth. These circuits put out two numbers whose sum is the result of the multiplication. If a single output number is required then the depth of the multiplication circuits increases respectively to 4.48 log₂ n and 5.95 log₂ n.We also get {, , }-formulae of sizeO (n ^3.13) and {, }-formulae of sizeO (n ^4.57) for all the output bits of a carry-save addition ofn numbers. As a consequence we get formulae of the same size for the majority function and many other symmetric Boolean functions.     

Synthesis of elastic structures with controlled forces

An analytical model is presented for synthesis of elastic structural systems under external loads and desired “controlled forces”. In the first stage, the optimal force distribution and the final cross sectional dimensions are chosen, solving an optimization problem with elastic compatibility temporarily excluded. In the second stage, the force due to the external loads is determined for the optimal structure by elastic analysis, and the desired controlled force needed for the optimal cross sections and force distribution is obtained by subtracting the above result from the optimal force of the first stage. The final design which has been determined in the first stage, satisfies both conditions of equilibrium and compatibility. It is a lower-bound solution for a similar incontrolled elastic system. In some cases the first-stage optimization problem may be cast in linear programming form. Numerical examples of continuous beam and indeterminate truss demonstrate application of the proposed method.     

A bounding procedure for synthesis of prestressed systems

Optimal design of indeterminate prestressed concrete systems is stated in a nonlinear programming form. The design variables are the concrete dimensions, tendon coordinates, and prestressing force. The constraints are related to various behaviour and design requirements and the objective function represents the overall cost. On the basis of the transitivity property, a lower bound on the concrete volume is determined by solving a reduced problem. The corresponding minimum prestressing force, calculated by linear programming, is an upper bound. Similarly, a lower bound on the prestressing force is determined by assuming the maximum concrete dimensions. Based on the two bounding solutions a lower bound on the objective function is evaluated. An efficient design procedure is proposed. The best of the bounding solutions is first checked for optimality. The search is then continued, if necessary, in the reduced space of the concrete variables using a feasible directions technique. For any assumed concrete dimensions a reduced linear programming problem is solved. It is shown that the potentially critical constraints at the optimum of the latter problem can be identified a priori. The solution methodology and the efficiency of the proposed procedure are illustrated by some examples.     

On regional nonlinear H-filtering

The structure of the nonlinear H^∞-filter in the neighborhood of the estimated trajectory is investigated and a bound on the size of the neighborhood that allows this structure is determined, both for finite and infinite horizons. Riccati inequalities that depend on the estimated trajectory are derived for finding the filter gain matrix and an algorithm for calculating the bound on the size of the above neighborhood is presented. Explicit formulas are obtained in the infinite horizon case for the minimum achievable disturbance attenuation level, the size of the neighborhood, and the corresponding filter gain.     

Btu tax as a revenue option: Its impact on agriculture in the USA

The paper investigates the impact of the imposition of a broadly based energy tax on the US economy in general and the agricultural sectors in particular. The analytical approach used in the analysis consisted of a general equilibrium model composed of 12 producing sectors, 13 consuming sectors, six household categories, classified by income, and the government. The effects of a 10 cents per million Btu tax on energy on prices and quantities are examined. The results are revealing. For example, a 10 cents per million Btu tax on energy imposed at the point of production would result in lower output by the producing sectors (by about $9.154 billion), an increase in the consumption of goods and services (by about $20.292 billion), and a reduction in welfare (by about $4.30 billion). The government would realize an increase in revenue of about $6.356 billion. If the Btu tax were imposed at the point of consumption, there would be lower output by the producing sectors (by about $5.88 billion), an expansion in the consumption of goods and services (by about $19.830 billion), and a reduction in welfare (by about $7.066 billion). The government would realize an increase in revenue of $6.688 billion. The agricultural sectors would be minimally impacted. For example, if a 10 cents per million Btu tax were imposed at the point of production, output in the program crops sector would rise (by $8.3 million), output in the livestock sector would decline (by $83 million), output in the all-other-agriculture-commodities sector would be reduced (by $118 million), and output in the forestry sector would rise (by $34.7 million). If the Btu tax were imposed at the point of consumption, output in the program crops sector would fall (by $38 million), output in the livestock sector would decline (by $42 million), output in the all other agriculture commodities sector would be reduced (by $94 million), and output in the forestry sector would rise (by $221 million).