Biomedical subjects

P F Barker

Publications and source records attributed to P F Barker.

3 recordsLinked to original sources

PubMed2004

Optical stark decelerator for molecules.

We demonstrate a single stage optical Stark decelerator for neutral molecules which is capable of reducing the translational energy of benzene molecules within a molecular beam by 15% in a single pulsed Gaussian optical field of 15 ns duration. The change in velocity induced by the optical potential is measured by the change in the time of flight of benzene molecules ionized by a second optical field after the slowing field is turned off. A maximum reduction in the velocity of 25 m/s was measured using a single Gaussian beam with a peak intensity of 1.6 x 10(12) W/cm(2) corresponding to a maximum well depth of 253 K.

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PubMed2003

Collisionless Boltzmann equation with an external periodic traveling force: analytical solution and application to molecular optics.

We present an analytical solution to the collisionless Boltzmann equation for describing the distribution function of molecular ensembles subject to an external periodic traveling force of pulsed optical fields. We apply our solution to study a pulsed standing wave mirror for neutral molecules, recently proposed [P. Ryytty et al., Phys. Rev. Lett. 84, 5074 (2000)]. Using our analytical solution we study the effects of the anharmonicity of optical potential on the reflectivity of the molecular mirror and the corresponding optimal pulse duration. We demonstrate that the reflectivity of the molecular mirror can be significantly improved by optimizing the pulse duration of the external optical fields when taking into account the anharmonicity of molecular motion.

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PubMed2001

Geochemical tracing of Pacific-to-Atlantic upper-mantle flow through the Drake passage.

The Earth's convecting upper mantle can be viewed as comprising three main reservoirs, beneath the Pacific, Atlantic and Indian oceans. Because of the uneven global distribution and migration of ridges and subduction zones, the surface area of the Pacific reservoir is at present contracting at about 0.6 km2 x y(r-1), while the Atlantic and Indian reservoirs are growing at about 0.45 km2 x yr(-1) and 0.15 km2 x yr(-1), respectively. Garfunkel and others have argued that there must accordingly be net mantle flow from the Pacific to the Atlantic and Indian reservoirs (in order to maintain mass balance), and Alvarez further predicted that this flow should be restricted to the few parts of the Pacific rim (here termed 'gateways') where there are no continental roots or subduction zones that might act as barriers to shallow mantle flow. The main Pacific gateways are, according to Alvarez, the southeast Indian Ocean, the Caribbean Sea and the Drake passage. Here we report geochemical data which confirm that there has been some outflow of Pacific mantle into the Drake passage--but probably in response to regional tectonic constraints, rather than global mass-balance requirements. We also show that a mantle domain boundary, equivalent to the Australian-Antarctic discordance, must lie between the Drake passage and the east Scotia Sea.

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