Self-assembly of mesoscopic metal-polymer amphiphiles

The assembly properties of two- and three-component rod-like building blocks consisting of gold and polymer block domains have been investigated. These structures behave like mesoscopic amphiphiles and form a series of single-layer superstructures consisting of bundles, tubes, and sheets depending upon the compositional periodicity. Unlike molecular systems, the template used to initially synthesize them plays a critical role in the assembly process by prealigning them in a manner that facilitates their assembly by optimizing the correct collisional orientation upon dissolution of the template. Tubular structures with tailorable diameters can be assembled in a predictable manner on the basis of an estimate of the hybrid rod packing parameters.     

Optically induced entanglement of excitons in a single quantum Dot

Optically induced entanglement is identified by the spectrum of the phase-sensitive homodyne-detected coherent nonlinear optical response in a single gallium arsenide quantum dot. The electron-hole entanglement involves two magneto-excitonic states differing in transition energy and polarization. The strong coupling needed for entanglement is provided through the Coulomb interaction involving the electrons and holes. The result presents a first step toward the optical realization of quantum logic operations using two or more quantum dots.     

Seismic determination of elastic anisotropy and mantle flow

When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.     

An all-optical quantum gate in a semiconductor quantum dot

We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previously demonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate. The truth table of the gate shows the features of an all-optical quantum gate with interacting yet distinguishable excitons as qubits. Evaluation of the fidelity yields a value of 0.7 for the gate operation. Such experimental capability is essential to a scheme for scalable quantum computation by means of the optical control of spin qubits in dots.     

HTLV-III in the semen and blood of a healthy homosexual man

Human T-lymphotropic virus type III (HTLV-III) is the probable etiologic agent for the acquired immune deficiency syndrome (AIDS). HTLV-III was isolated from semen and blood of a healthy homosexual man whose serum contains antibodies to HTLV-III. The finding of virus in semen supports epidemiologic data that suggest that AIDS can be transmitted sexually. In addition, the demonstration of HTLV-III in the blood and semen of a healthy individual establishes an asymptomatic, virus-positive carrier state which may be important in the dissemination of HTLV-III and, consequently, AIDS.     

Coincidence Counting in Time-of-Flight Mass Spectrometry: A Test for Chemical Microhomogeneity

Coincidence counting techniques have been combined with time-of-flight mass spectrometry in the examination of surfaces for chemical microhomogeneity. A mathematical formalism was developed to describe the principles underlying this coincidence counting technique and was used to produce a quantitative method for handling the data obtained. This technique of testing for chemical homogeneity has been demonstrated with a sample that consists of a physical mixture of polystyrene and crystals of NaF which were tenths of micrometers in diameter. Ultimately this approach is expected to be useful for the routine testing of surfaces for chemical homogeneity at the level of tens of nanometers.     

Genetic analysis of digestive physiology using fluorescent phospholipid reporters

Zebrafish are a valuable model for mammalian lipid metabolism; larvae process lipids similarly through the intestine and hepatobiliary system and respond to drugs that block cholesterol synthesis in humans. After ingestion of fluorescently quenched phospholipids, endogenous lipase activity and rapid transport of cleavage products results in intense gall bladder fluorescence. Genetic screening identifies zebrafish mutants, such as fat free, that show normal digestive organ morphology but severely reduced phospholipid and cholesterol processing. Thus, fluorescent lipids provide a sensitive readout of lipid metabolism and are a powerful tool for identifying genes that mediate vertebrate digestive physiology.